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1987 Husqvarna 430 WR: The big bore two stroke gets a manual transmission.

There was a Husqvarna 430 two stroke back in 1981, but that was an air cooled dual shock drum brake dinosaur. By 1986 when a 430 two stroke was again available it was water cooled and the chassis was considerably augmented with a large box section aluminum swing arm on a mono shock with linkage. For 1986 the 430 motor was only available with the three speed automatic transmission. For 1987 the 430 motor was finally available with the standard six speed manual transmission, and the 400 motor was dropped. The 1987 Husqvarna 430 WR appears to be a lot like the 1986 Husqvarna 400 WR it replaced. At first glance it looks like just a big bore kit and some new plastic on the old bike. The differences are however much more substantial. It might be the same basic motor and chassis, but a new fatter pipe and bigger muffler yield a dramatically different sounding and feeling power band and a few tweaks to the chassis make for a faster and much different feeling bike.

The Big Bore Kit
The Rusty Hulk
From Rags to Riches
Riding the 1987 Husqvarna 430 WR
Head to Head Comparison: '86 400 Vs. '87 430
Port Height

The Big Bore Kit

The increase in displacement comes entirely from a bigger piston in a bored out cylinder liner. The 430 motor is on the same transmission and bottom end as the 1986 400 motor with the same 74mm (2.91") stroke length, just with a substantially larger 86mm bore versus the 82.5mm bore of the 400 motor. Even though it is the same bottom end on both motors the 1987 430 motor does get a new lighter connecting rod. This has been a much talked about upgrade, and everyone seems to agree that the lighter connecting rod does result in a much better balanced engine that runs smoother with less vibration. Apparently some people have even put the '87 rod into the '86 400 motor to get the same lower vibration running. The lighter connecting rod would always tend towards smoother operation, but it appears that like many Husqvarna motors the '86 400 WR motor was under balanced, that is it dramatically benefits from a lighter reciprocating assembly on the exact same crankshaft.

The ports height appears to be the same on the 400 and 430 motors, the reeds and reed blocks are the same and both motors use the same 38mm Mikuni round slide carburetor with the same Mikuni 400 main jet. What is different though are the expansion chambers. Both motors are the same non-power valve configuration, but the '87 430 WR has a much fatter pipe. The '87 430 WR also has a substantially larger diameter muffler with the same spark arrestor tip as the '86 400 WR. The expansion chamber outlet and muffler inlet pipe is also a larger diameter on the '87 430 than on the '86 400. All in all it is just a much more substantial exhaust system on the '87 430 WR, and this is where the performance difference comes from.

The Rusty Hulk

I had seen the ad for a basket case of an old 1987 Husqvarna 430 WR a few days previously, but I was not feeling like I needed another dirt bike. Especially not another two stroke. Then I was out riding the '86 Husqvarna 400 WR and having a great time rowing the gear box through the narrow and lively power band. The big two stroke was running pretty much at it's best, with just enough over rev to almost get between fourth and fifth gears without using the clutch.

When I got back from the short ride I decided to try to buy the old '87 430 WR if it was still available. As it turns out I did not have to worry much about that particular rusty hulk selling quickly. It looked like it had been sitting neglected for about the last decade. The guy who was selling it wanted $700, and he said he had all the parts for it in a big plastic tub.

When I got out to look at the bike he did indeed have a large tub of parts for the partially disassembled bike, but some things were obviously missing. Most of the bolts were missing, and the reed block was missing. The cylinder, head, piston, pipe, air box, filter cage, filter hold down and air box cover were however all in the box and the carburetor was still on the bike. The bike was rough and somewhat rusty, but it was mostly all there. The front brake was mush, and the rear brake was adjusted all the way in and very low but still grabbed a little bit. In light of the missing reed cage I offered $500, but the seller would take no less than $550. I knew it was a mostly complete Husqvarna and well worth the $700, but it looked really bad all taken apart and rusty like that.

When the seat fell off in the road driving down the street I was beginning to feel a bit depressed about having wasted $550. When I looked in the box more carefully I saw that a bunch more pieces were also missing. It was a horrible basket case to be sure, but the more I looked at it the more interesting differences between the '87 430 WR and the '86 400 WR that I had never noticed before began popping out. The first thing I noticed was that huge pipe, with a very big additional bulge out towards the end near the outlet. I also noticed a two piston Brembo caliper on the front just like the two piston Brembo caliper on the 1991 Husqvarna dirt bikes.

I was beginning to get very interested in just how this '87 430 WR would run compared to the '86 400 WR I had been riding sometimes over the past year. It was this interest and enthusiasm that kept me from totally losing hope when I realized that what I had thought was the piston pin rolling around in the bottom of the plastic tub was in fact just a piece of dirty white plastic tubing. I also realized that the cylinder studs and nuts were missing. The other missing bolts were less of a problem, but the missing cylinder studs presented something of a challenge.

From Rags to Riches

Undeterred by the missing pieces and general poor condition of much of the bike I started working on getting the parts required to put the motor back together. The guy selling the bike had stressed over and over again that he thought the cylinder was still in good enough condition to run with a new ring. When I measured the taper and out of round it looked pretty darn good. There was some wear near the exhaust port, but it was pretty minimal really. The ring was however very badly worn. It was right near the edges of the exhaust port where the ring was worn down substantially. When I put the ring in the top of the cylinder I could see light through large openings there where the ring would go over the sides of the exhaust port. When I measured the wall thickness of the ring there where it was worn down it was 0.006" less than on the intake side of the ring. The end gap was also extremely wide at 0.030". Another problem with the ring was that it appeared to have been too narrow for the ring groove in the piston. The ring groove had a bit of wear so that it tapered out a small amount towards the outside, but even down at the bottom of the ring groove it measured 0.067". The ring sides were also worn a bit so that it was thinner on the inside than on the outside, but even the outside was only 0.058". It looked to me like someone had put a 1.5mm ring into a ring groove cut for a 1/16" ring, there was just way too much side clearance.

Obviously the motor needed a new ring, but replacements only appeared to be in stock in England for a ridiculously high price of $70 plus shipping. Since the 1/16" thickness is very common I figured I could find some ring that would fit, I just needed to figure out how to find the dimensions of rings. My first luck was finding that many older Harley Davidson V-Twin motors used 1/16" thick rings on 3-7/16" bores. If one of these was the correct wall thickness it could be end gapped down into the 86mm bore with little difficulty. What I found was that the Hastings Manufacturing Company in Hastings Michigan had a bunch of their piston rings listed by size on their website. Surprisingly the 1/16" thick rings were not all that prevalent, most of the rings for that approximate bore diameter were 0.057" thick. I did find one 1/16" ring listed for a 3.390" bore diameter with a wall thickness that was marginally too wide. I had measured the ring groove depth on the piston out of the 430 motor as 0.146", but there was just that one ring listed and it had a 0.146" wall thickness. The next smaller wall thickness I could find was 0.130", which was a whole lot too small. The 0.130" wall thickness ring would have sort of worked, but the 0.146" deep ring groove really needed more like a 0.140" ring.

I ordered the Hastings 42861 ring, which was in stock and shipped out from Michigan to California in just three days for a somewhat high seeming $12 shipping charge. The price of the ring also seemed extremely high, and the total was $36. A lot less than approximately $100 for a Husqvarna ring, but really very expensive seeming for just a single loose ring. When I asked the lady handling direct sales for Hastings all she could say about the high price was "probably chrome" in a thick Midwest accent.

The piston pin and small end bearing were easier as just about all two stroke dirt bikes from the past 30 years have used 18mm wrist pins with a 22mm small end bore. The pin I used was a Wiseco S477 which fits KTM 300 two strokes and a bunch of Polaris and Ski Doo motors from the mid 1980's through about 2004. I also could have just as easily used a Wiseco S508 pin which fits the '87-'89 Kawasaki KZ 250 and the '91-'97 Yamaha YZ 250. Both pins have the same 13mm I.D. and are listed as straight, non-tapper and non-chrome pins and both had about the same retail price of $13. I went with the S477 just because it was a bit shorter so it did not have to be cut down as much to fit the Husqvarna piston. The small end bearing was even easier. The Husqvarna 430 motor uses spacers on the sides of the bearing, and these were also missing from my pile of junk parts. What I did was just order a 23.5mm long bearing for a Kawasaki KZ 250 which sufficiently took up the slack on the 20mm wide connecting rod small end bore. The Wiseco B1022 bearing was similarly reasonably priced at just $12 with free USPS 1st class shipping on the $25 combined pin and bearing order from the same retailer in Texas. At least the parts I needed to rebuild the motor were all small and light which made for mostly very inexpensive shipping charges.

While I was waiting for all the parts to arrive I got to looking over the original stock Mahle piston. It was in good condition with only the slightest bit of wear on the skirts. With all of the difficulties with getting a ring, pin and bearing most people would have just ordered a whole new Woessner piston kit for $200. Not only was I wanting to keep the parts total low for my basket case junker build, but I also had a bit of a desire to run the original Mahle piston to see what it could do. The Mahle piston was generally a pretty nice piece, with long slender skirts and a thick crown. It was however also really very heavy at 359g. The long full two stroke skirts do unavoidably add some weight, but 359g for an 86mm piston is extremely heavy.

The thing about two strokes though is that piston weight does not actually tend to be all that much of an issue. Cylinder port two strokes run over only a very narrow range of engine speeds, and in order to get best possible overall performance this narrow range of engine speeds generally needs to be down at moderate mean piston speeds. Piston weight is also normally very significant for medium and light load efficiency at slightly reduced engine speeds, but cylinder port two strokes typically just are not very efficient. A lighter piston is still better, but it does not make the dramatic difference that a lighter piston in a four stroke does.

As I looked at the stock Mahle piston though it just looked so easy to take some weight off. There was this big chunk of extraneous material on the outside of the pin bosses screaming to be cut off. And under the pin bosses Mahle had included a little round indentation suggestive of a hole through the long heavy pin bosses. In about ten minutes with a hand grinder and a drill I had the Mahle piston down to 330g, a substantial nine percent weight reduction. Quite a lot more material could have come off for an even lighter piston, but just as I was being stingy with the cost of replacement parts I was very stingy about engineering time on cutting down the piston. There just did not seem to be much reason to try to go lighter. Since the 18mm pin seemed a lot skimpier on the Husqvarna 430 than on a 250 or 300 I was however pleased to have some substantial reduction in piston weight.

When the ring arrived it was exactly the size listed on hastingspistonrings.com, 0.0620" thick and 0.146" of wall thickness. When I dropped the ring for a 3.390" bore into the 86mm (3.386") bore it fit perfectly with a 0.008" end gap. That seemed strange, an 0.008" end gap in a 3.386" bore would be about a 0.021" end gap in a 3.390" bore. Why had the new ring come pre-gapped with such a wide 0.021" end gap for the listed 3.390" bore diameter? To add to the mystery it did not look anything like any sort of chrome or other fancy ring. It had no noticeable plasma moly coating on the ring face, and it appeared to be just a plane cast ring. The 0.008" end gap probably would have worked, but I opened it up to a 0.015" end gap just for good measure. Wiseco recommends a ring gap of 0.014" for their piston rings in a three inch bore, and that seemed about right to me. While I was grinding a bit off of the end gap I also had to clearance the ends of the new ring for the locating pin on the two stroke piston. That was pretty easy as the dimensions of the small cutouts are not all that critical. The ends just have to be radiused so that they clear the small locating pin when the end gap is closed up all the way.

The problem with the ring was that the 0.146" wall thickness really was too big. The ring seemed to stick out from the ring groove slightly, and this was not acceptable. As it turned out it was really very easy to clearance the ring. I just ran a little grinding wheel around inside the ring a several times and in a few minutes I had it cut down to a fairly uniform 0.142" wall thickness. The wall thickness of course did not come out perfectly uniform, but since only three percent of the original wall thickness was removed the lack of uniformity was slight and insignificant.

Not only was the Hastings 42861 ring rather expensive, but it also involved a fair amount of additional work to cram it into the Husqvarna 430 motor. In the end though all the pieces went together nicely. The pin was much easier to cut down, needing just a small amount cut off of each end. I did not even bother to measure or chuck the pin in the lathe, I just held the pin in my right hand and the hand grinder in my left hand and knocked some material off of both ends of the pin. A few test fit attempts with more material taken off and the pin was ready to go.

I did have one slight problem with the pin though, it did not come with circlips. I thought replacement piston pins always came with new circlips, but this one did not have any circlips included in the package. As is typical I was itching to get the motor back together after waiting many days for the parts to be shipped in, so I just threw the motor together in one day anyway. For circlips I modified some external circlips of approximately the correct size. This was sort of a mistake as it was more difficult than I had expected and the end result was not all that good. Really the biggest problem with my modified circlips is that they fit tight, so the next time the engine is disassembled it may be a bit difficult to get them out.

Continuing the theme of going supper cheap on the basket case resurrection I decided to reuse the original head gasket instead of ordering a new gasket set. This was a wild sort of decision to make as the head gasket was not in all that great of condition and the base gasket was entirely missing. The first thing I had to do to reuse the head gasket was figure out what base gasket thickness would be required.

The 1987 430 motor is listed as having a 12.6:1 compression ratio, which is slightly higher than the 12.3:1 compression ratio of the 1986 400 WR motor. The cylinder head for the 430 is a different part number than the cylinder head for the 400, and my cylinder head actually has "430" stamped into it. Somehow though I still expected the cylinder heads to be identical. What did seem to be different was the height of the cylinder. The 1987 430 cylinder measured 5.040", and as near as I could tell with the bike fully assembled the cylinder on the 1986 400 WR appeared to be 5.030". Just going up from an 82.5mm bore to an 86mm bore with everything else staying exactly the same does not work out to the advertised compression ratios. With the 0.010" difference in cylinder height though it would be the difference between a 12.1:1 compression ratio on the 400 and a 12.6:1 compression ratio on the 430. In some sources the 1986 400 WR motor is in fact listed as having a 12.1:1 compression ratio. It seemed likely to me that everything else was the same on both motors, and the increase in compression ratio was in fact due only to the increase in bore size. My 1986 400 WR has a 0.045" thick base gasket, and all of the parts sources list the same base gasket for both the 400 and 430 motors. With a 0.045" thick base gasket the 1987 430 parts I had appeared to yield a 12.6:1 compression ratio. The combustion chamber volume of the head was looked close to 28cc when I rather crudely measured it by weighing a glass of water before and after filling up the upturned head. With the 0.045" thick head gasket and the 0.015" that the piston was down in the cylinder bore with the 0.045" base gasket this all worked out to a 12.6:1 compression ratio on the 430 motor. To get this base gasket thickness I used a piece of 3/64" gasket paper from the auto parts store. 3/64" and 1/32" seem to be the most common thicknesses for gasket paper.

For cylinder studs I just cut up a one meter length of low carbon M10 - 1.5mm threaded rod. Most mechanics would be alarmed at the idea of using that cheap $7 piece of soft hardware store all-thread for head studs, but again the parts were just dramatically oversized. The 10mm cylinder studs are the same as on the 98mm bore 610 four stroke, so for the 86mm bore 430 two stroke they are way plenty big. I did splurge and go with very expensive "Top Lock" nuts at sixty cents each from Ace Hardware to get a bigger nut on the studs. I did not want lock nuts, so I just ran a tap through each nut before installing them. This opened the "Top Lock" nuts up to be just plane oversize nuts with very little effort. There might not have been any real oversize M10 nuts available locally, but the top lock nuts that were available locally were also just cheap soft low carbon steel that was very easy to run a tap through. Even with the cheap low carbon studs and nuts I ran the torque down past the 29 foot pound Husqvarna specification with no difficulty. I went right up to the 37 foot pound torque spec for the M10 cylinder bolts on the 610 four stroke and the soft nuts on the soft low carbon threaded rod gave no signs of trouble. I should also admit though that when I put the four strokes together I do tend to torque the hard M10 studs and long hard nuts down to more like 40 foot pounds just to make sure there will be no head gasket sealing problems.

At first I had been thinking that the reed cage was going to be an expensive item to replace, but it turns out that all of the 250, 400, 430 and 500 Husqvarnas throughout the 1980's used exactly the same reed block and reeds. Since so many bikes used the same reed block it is pretty easy to get one used. I just ordered the cheapest used reed block listed on eBay for $21 delivered, and as a bonus when it arrived the original Husqvarna reeds were even in perfect condition. New Boyesen 616 reeds seem a bit pricy at around $40 these days, but they certainly are readily available. The reed block I got was off of a 1986 Husqvarna 250 XC. Although it is identical to the reed block on the 1986 400 WR there is a plastic insert snapped into the 250 reed block. I mulled over what this insert might do, and what I came up with was that it would slightly increase low end response. I decided to keep the plastic insert installed and see how it would work on the 430 motor. The 1986 and 1987 parts manuals list this plastic insert only for the 250 motors, not for the 400, 430 or 500 motors.

Before the rebuilt motor was ready for a test ride though there were some issues with the chassis that had to be addressed. When I took the swing arm off I found that the pivot bearings on the right hand side were toast. The rollers were broken up into little pieces that fell out all over the place when I pulled the dry as a bone bearing apart. The left hand side was still intact, but there was some play in it.

The inner races were not in great condition but they might have been serviceable. Those inner races are the same as on all of the later Italian 350, 410 and 610 four strokes, but they have never seemed to be available as new replacement parts. I took a chance and ordered a whole swing arm off of a 1986 Husqvarna 500 CR that was on eBay for $37 delivered. The seller said the bearings were good, which turned out to be only partially true. The needle bearings were broken to little pieces and useless, but the inner races were in fairly good condition. The inner races were somewhat pitted with considerable surface cracking, but dimensionally they were within 0.001" of new. That was a lot better than the worn out junk that came out of the '87 430 WR showing as much as a 0.010" smaller diameter.

At first I had been thinking about using the whole '86 swing arm on the '87 bike, but before the part even arrived I realized that the linkage and linkage mounting points are totally different from '86 to '87. I would find out later that this has some other significant consequences beyond the swing arms not being interchangeable.

For bearings I ordered a set of four new HK2218RS drawn cup needle bearings, but I had measured incorrectly and this was not the size that the Husqvarna swing arm takes. The old bearing shells were in such horrible condition after I pounded them out that I got the width measurement wrong. I should have been more careful in measuring the swing arm and inner races, but instead I just made a quick estimate based on the twisted and mangled shells that came out assuming that it would be a whole millimeter bearing width. The 18mm wide bearings were a bit too wide. When I carefully measured the inner races though I found that the next size smaller 17mm wide bearings came out a bit too small. To get the project together I just hit the HK2218RS bearings with the hand grinder to take 0.015" off of each thrust surface. This was more work than I would have liked, but at least I did not have to wait for another $50 set of bearings to show up. Grinding the new bearings shell down turned out great, and the swing arm went on very securely with no wiggle and no binding. Well, not much binding anyway. When I torqued the swing arm pivot bolt down to 70 foot pounds the inner races did bind a small amount on the roughly hand ground thrust surfaces of the bearing shells. It was only about a five pound binding force at the rear axle, and as I moved the swing arm up and down this binding force diminished.

The linkage bearings were in pretty good condition. The main needle bearings on the pivot were in excellent condition, just a bit dry. The other linkage bearings which are just bushings were worn and had some play in them. When I turned these bearings 180 degrees though they tightened up to where there was no play. It was easy to see why the linkage bushings had failed, the zirk fitting was missing and it's threaded hole was packed full of mud. Thankfully zirk fittings are all standard sizes and the smallest size in my little box of selected zirk fittings went right in.

While I had the rear wheel off I noticed that the low rear brake was not due to worn out brake shoes. The shoes were nearly new, it was the aluminum drum that was severely worn. This bike obviously had gotten ridden quite a lot at some point in it's long term of service. Since the brake drum is part of the hub this wear is a very severe problem. Looking carefully at the brake drum though it seemed that there was still a substantial amount of material left. It was worn severely, but it was not in any immediate danger of breaking through under a load.

To get the bike going with the parts I had I fabricated some engagement plates out of eighth inch mild steel plate and screwed them to the ends of the brake shoes with flush mount flat head 8-32 machine screws. This was a lot of work, but it turned out well. The rear brake was back up to the center of the adjustment range and looked like it would work well for a while. I have ridden a number of bikes with drum brakes and I have always found that a set of shoes goes for a really long time. There is just a lot more material on a set of drum brake shoes than on a set of disk brake pads. It was probably riding in lots of thick sticky mud that toasted that drum. In normal riding the drum brakes seem to go for a really very long time.

The somewhat soft mild steel engagement plates will tend to wear faster than the hard engagement plate on the stock shoes. If the plates are kept well greased with a dab of high quality water proof greas at each tire change though they will probably last fairly well.

When I first tried to get the front brake system working the caliper appeared to be plugged up solid. I pumped 60psi of air into the line with the master cylinder removed, but nothing came out of the open bleed screw. The gunk that had come out of the master cylinder was pretty grim looking with lots of thick black chunks in it. I cleaned out the master cylinder and flushed the line through. Then I left the bleed screw open with brake fluid in the master cylinder and line. I was thinking that I might have to take the caliper apart to free it up, but amazingly after the new brake fluid soaked into the caliper for a few days it started flowing. Even more amazingly the master cylinder worked perfectly once it had fresh fluid in the system. At first the caliper pistons were stuck, but once I got the system bled through I was able to break the pistons free just by squeezing the brake lever.

Riding the 1987 Husqvarna 430 WR

When I first kicked the re-ringed motor it would not bump over. The motor appeared to spin freely, but each time I gave it a kick it just stopped abruptly on compression. I was using the same procedure as on the '86 400 WR, I would bring the engine up on compression and then wait for it to just bump past compression and come up on top dead center. When I kicked the 430 though it would only spin around one revolution and then it would just stop when it came up on compression again. I kicked the engine a bunch of times, but each time it was like kicking a stump. My ankle began to get sore and I was very frustrated that I could not get the bike to kick over. It was not that the motor was kicking back, it was just that it would not go past compression. When I tried to kick the motor with the spark plug wire removed it was exactly the same.

When I rolled the bike down a small hill in sixth gear I could get the engine to turn over a bit, but with no compression release this was not working well and the engine still would not fire up. I did get the engine to spin over pretty good once, and it seemed like it was firing a bit also. After this little near firing the cranking compression came up quite a bit and the bike was even more difficult to get to spin over in sixth gear. When the engine did not fire up and run even after it was spun over pretty good I looked for other problems and I found that the fuel inlet was plugged. I had taken the main jet out and I had taken the top of the carburetor off, but the carburetor had looked so very clean that I had not bothered to disassemble it further. As it turns out there was some dirt in the fuel inlet that had been sitting exposed all those years.

The 38mm Mikuni had the same Mikuni 400 main jet as the '86 400 WR, this approximately 172 size main jet is listed as the stock jet for both bikes. What is different about the carburetors on the '86 400 WR and the '87 430 WR is the needle. The '86 400 WR is listed as taking a 6DH3 needle, and this is what was in the bike when I got it. The stock needle clip position for the '86 400 WR is listed as the 4th groove from the top, but I have run that bike with the needle clip in the 3rd groove from the top and that seems way plenty rich through the lower to middle throttle openings. The '87 430 WR on the other hand is listed as taking a 6DH20 needle, and that is what was in the bike when I got it. The stock needle clip position for the '87 430 WR is listed as the 3rd groove from the top, and I stuck with this stock position.

Once I got the fuel flowing into the carburetor bowel it looked like the bike should start. There was a nice powerful looking purple spark from the Motoplat Mini 6 ignition system when kicking the engine over with the plug out, so everything seemed to be in place for the bike to fire up.

Eventually I put on a pair of very sturdy riding boots that fit somewhat too tightly and I buckled them down very securely. With my ankle essentially totally immobilized I gave the bike a big flying leap of a kick and it did bump over. A few more kicks and I got it to fire up.

As I usually do with a new bike I rode it slowly up the driveway and back and changed the transmission oil. I had already drained the thick gunk out of the transmission and filled it with 10-40 motor oil before firing the bike up, but it still needed another change to come clean.

With the bike mostly all ready to go and a tank of 60:1 premix I headed out for a little test ride. The first thing I noticed was that the 430 pulls a lot harder a lot sooner than the '86 400 WR. It really was giving a pretty good pull all the way down to like 4,000RPM. Once well warmed up it was pulling all the way down to 3,500RPM, but the torque was a lot lower down at less than 4,000RPM. The torque then increased dramatically up to a substantial pull at 5,000RPM. This thing really does hit a lot sooner than the '86 400. The power band was also broader, with a strong powerful pull up to 6,000RPM. That first ride it was slow flame front travel speed gasoline that I happened to have. I noticed right away that it was slow flame front travel speed gasoline as the engine was lighting off most easily way down at the bottom from 4,000 to 4,500RPM, but then was requiring a big twist of the throttle to keep pulling up to where maximum torque was generated at 5,000 to 6,000RPM. The engine was reliably pulling over a range of engine speeds, but only when well warmed up and with a big twist of the throttle on a big pull. Even with only about a 60:1 mix ratio the bike was smoking quite a lot at idle on the slow flame front travel speed gasoline.

The next thing I noticed about the 430 is that it has over rev like a power valve two stroke. At the top of the power band the engine did not just abruptly stop making power like the '86 400 WR always does. No, the '87 430 WR was running very much like a Japanese two stroke with a power valve. On the slow flame front travel speed gasoline the engine would sort of stumble and cut in and out over a rather wide range of engine speeds from about 6,000RPM up past 7,000RPM. There was some power up there once well warmed up on a big pull with the throttle wide open, but it was a gradually decreasing sort of power up at the top. The 430 WR has lots of over rev like a power valve two stroke. The '87 430 WR might go flat up on top, but it certainly does make more power over a wider range of engine speeds than the '86 400 WR. Whether the '87 430 with over rev is better than the '86 400 WR with essentially no over rev is a matter of opinion. Broader power to get between the gears without slipping the clutch is undeniably a significant advantage. The over rev though is not necessarily such a great feature. I have always considered over rev to be a major point of distinction between Japanese dirt bikes and Husqvarna dirt bikes. Husqvarna dirt bikes have broad ramping up power bands with a short over rev that does not need to be used. Japanese dirt bikes on the other hand tend to have a narrow increasing power band with a broad gradually decreasing over rev that has to be used in every gear to go fast. Using the over rev all the time is not only slow, it also is not as much fun.

After the first little test ride the cranking compression had come up even more as the new ring seated in. Pushing down on the kick start lever to bring the engine up past compression was taking more force for a longer period of time. Interestingly though the engine was spinning over more easily and actually kick starting with less effort after the short run in. The cranking compression came up some, but the new ring also polished in against the cylinder wall to reduce friction. It turns out that it was the friction of a new somewhat rough ring face that was causing the bike to be so difficult to kick over.

The next several times I rode the 1987 Husqvarna 430 WR the gasoline was considerably different. It was somewhat faster flame front travel speed gasoline that also had a dramatically lower temperature of combustion potential. This resulted in a very narrow power band with hardly any over rev. There was actually still some torque to be had down below the power band, but it was weaker and it was requiring a very large twist of the throttle to get the engine to light off on late compression ignition down at those lower engine speeds from 4,000 to 4,500RPM. Then once the engine hit the power band at just under 5,000RPM it got harsh and tinny sounding and did not pull very hard. The engine would however run and make power in the power band from 5,000 to 5,500RPM with just small throttle openings. The problem with cutting out up in the over rev was also gone, there just wasn't any over rev at all. The engine just would not rev up much past 6,000RPM. I found myself slipping the clutch in every gear, and this turned up another problem with the bike.

The April 1987 Cycle World Magazine test of the 1987 Husqvarna 430 WR says that the clutch is weak and inconsistent. When I took the clutch cover off I found out why. The '87 430 WR has a nice one piece steel basket, but the disks are all aluminum. Aluminum "steel" disks and aluminum "fiber" disks. The "fiber" on the disks also looks horrible. It does not look like any kind of Husqvarna clutch material I have ever seen. It looks like recycled Pepsi bottles melted onto the aluminum disks. And that is what it feels like also. Perhaps these are aftermarket disks. I certainly hope that they are unusually crappy aftermarket disks because they sure don't work like any Husqvarna clutch I have ever used.

Of course part of the problem was that the water pump seal was leaking. When I pulled the shaft and seal out I could see that the seal was loose and wiggled around on the shaft. The inner of the two ball bearings on water pump shaft was also very worn out. The outer bearing was still smooth and tight, but the inner bearing was wiggling around a lot. Replacing the SKF 608 bearing and 8-18-5 seal was easy and cheap as the parts were in stock fairly close by with very inexpensive USPS First Class shipping on the small items.

With water staying out of the transmission oil the clutch seems to be working better, but it is still no Husqvarna clutch as far as I am concerned. I see that there is a clutch kit with steel intermediate plates available for the '87 Husqvarna , so if the plastic soda bottle friction material and aluminum "steel" disks don't work out there is actually something I can replace it with.

The two piston Brembo caliper on the 1987 Husqvarna 430 WR does work great. It is on the same 230mm rotor diameter as the 1986 Husqvarna 400 WR, the difference is in the amount of piston area in the caliper. The 1986 400 WR has a single piston Brembo caliper on the same master cylinder. This makes for less than spectacular braking performance. The front brake on the '86 400 WR works fine, it just takes more force at the lever and the bike usually does not end up slowing as quickly. The two piston Brembo caliper on the '87 430 WR gives braking performance much more like the same two piston Brembo caliper delivers on the 1991 Husqvarnas with the larger 240mm front disk. The difference between the 230mm 1987 disk and the 240mm 1991 disk is noticeable, but it is a slight difference. It feels like the 5% difference in braking power that the 5% difference in disk diameter would suggest. This is a obviously a much smaller difference than the 2:1 difference between the '86 single piston Brembo caliper and the '87 and up two piston Brembo caliper. They look like the same size pistons, and they feel like the same size pistons. It really is very nearly a 2:1 difference in braking performance between the '86 400 WR and the '87 430 WR. It is not that the '86 400 WR takes twice as long to stop. No, the single piston Brembo caliper is still capable of locking the front wheel on rather high traction surfaces. Instead it is a matter of the single piston caliper requiring nearly twice as much force at the lever, and this large amount of extra force means that it is not nearly as easy to modulate heavy braking. The '86 single piston Brembo caliper works much better for lighter braking in casual riding, when pushed hard it is difficult to modulate and is also just a lot more heavy work with the right hand fingers.

For heat dissipation under sustained heavy braking the 240mm 1991 rotor is considerably bigger than the 230mm rotor on the two strokes. It is not only the 5% larger swept area of pad contact but also the more substantial cooling slots in the 240mm 1991 rotor. The old 230mm rotor just has some holes drilled in it which does not provide nearly as much cooling. The reality though is that either the 240mm or 230mm rotor provides a substantial amount of thermal dissipating capability for a dirt bike. The only times I have had even the slightest hint of front brake overheating problems it was due to either unusually low boiling point brake fluid or unusually low melting temperature brake pads. In both instances the front brake gave out extremely easily on a long downhill, and switching back to more normal materials totally eliminated the brake fade problem. The one time I put DOT 3 brake fluid in the front brake on the 1991 WMX 610 back in around 2003 the front brake gave out on a long single track descent. The brake overheating was so bad that I had to stop several times on the downhill to let the front brake cool off. Each time the front brake gave out the lever suddenly went totally mushy and there was next to no front brake. After I got the bike stopped by diving off the trail in a rear brake induced sideways slide I could hear the brake fluid bubbling in the caliper. Switching back to DOT 4 brake fluid completely eliminated the boiling problem. I have never had any trouble with DOT 4 brake fluid boiling over in any of the Husqvarnas. The other time I had trouble with brake fade it was a new set of front pads I had just put on. They were some sort of extremely low temperature friction material that started smoking and lost braking performance on the same long single track downhill. With the smoking pads it was not quite as bad as with the boiling over brake fluid as the brakes began to fade a bit before they gave out all together. It was however still a similar maneuver of a rear brake induced slide to get the bike stopped the first time the pads started to smoke because I had ignored the warning signs of the first slight bit of brake fade and had continued to ride fast down the steep trail. Once I was aware that the new pads had an unusually low temperature friction material on them I was able to slow down and go easy on the front brake each time that it gave the slightest little hint of fading. Again switching to another brand of brake pads totally eliminated the brake fade problem. It was just that one set of pads that melted so unusually easily, the half dozen or so other sets of front brake pads I put on Husqvarnas before and after always worked extremely well and never exhibited the slightest bit of brake fade under any conditions. Both of these times that I had front brake fade trouble it was on the same long steep single track descent from 4,500 to 2,500 feet of elevation straight down the side of a mountain without even much in the way of switchbacks. A demanding brake test to be sure, but the brakes only gave trouble those two times with unusually low temperature fluid or friction material. Both times that the brakes gave out on that descent I did a bit of testing on wide open dirt roads afterwords to see how easily the brakes would overheat and give out. Both times I was amazed by how easily the brakes gave out when I pushed them just a little bit. The only reason that the bike made it out to the big single track descent both times was that I often ride casually without much heavy use of the brakes when I am just covering the miles out to a favorite riding area. Even riding fairly briskly on roads and trails I tend to let off early and coast for a while before very briefly grabbing the brakes just before entering a corner. That does not test the heat dissipating capabilities of the brakes anywhere near as much as staying on the gas all the way to the last moment and then braking heavily down into the corner. I do also often ride like that with lots of braking from the highest attainable speeds, and the brakes have always held up to it. Those two times that the brakes did give out on the big single track descent I just happened to be riding casually up to that point in the ride and I did not notice any problem with the brakes. With DOT 4 fluid and normal brake pads the 230mm rotor on the '87 430 WR probably won't give any overheating trouble either.

The 1987 Husqvarna 430 WR appears to have the same suspension as the 1986 Husqvarna 400 WR, they both use the same 40mm conventional Husqvarna forks and they both use the same Ohlins monoshock rear end. There are differences though. The '87 model has a new linkage with a somewhat different rising rate. The rising rate seems pretty similar when riding, both bikes feel like Husqvarnas. What is dramatically different is the suspension valving at both ends. There is just a lot more heavy duty damping on the '87 430 WR, and this makes it a faster bike for aggressive riding. On the '86 400 WR I have always run the compression clicker on the Ohlins shock in the middle of the adjustment range at about 12 clicks in out of 21. I started with the compression clicker on the Ohlins shock on the '87 430 WR at 10 clicks in out of 21, but this did not work at all. The rear suspension just was not moving at all. I backed all the way out on the compression clicker and this improved the rear suspension considerably. It is still on the stiff side under all conditions, but at least it does go up and down to absorb the bumps. I don't think the valving on the '87 Ohlins shock is really all that good, both the '86 Ohlins and the 1991 WP shock compression damping setups seem better. It is not all that bad of a valving setup on the '87 Ohlins shock though either. With the compression clicker turned all the way out it does work and the bike is pretty fast. Not fast like the 1991 WMX 610, but certainly very Husqvarna like. The rebound damping on the '87 Ohlins shock is also very substantial. A bit excessive feeling in many situations, but it is not extremely prone to packing up on any size of bumps either. It is a pretty good compromise setup, but it is certainly on the stiff and immobile side of the range of acceptable settings.

The 40mm conventional Husqvarna forks are also valved different on the '87 430 WR than on the '86 400 WR, and it is not just a different weight of oil either. The '86 400 WR forks tend to feel very compliant and comfortable over all types of terrain at all speeds, but they bottom pretty easily when falling out of the sky. The '87 430 WR forks feel somewhat stiffer on small low speed bumps, but then going a bit faster and plowing into ruts and big rocks they are actually plusher and more comfortable than the '86 400 forks. The best way to describe the difference is that the '87 430 WR forks are faster than the '86 400 WR forks. Not faster in the sense of less rebound damping being described as "faster rebound", no the '87 430 WR forks are just faster in that they allow the bike to go faster over rough challenging terrain. The '87 430 WR forks also seem better able to handle big impacts falling out of the sky on flat landings from jumps, but this is not really what either the '86 400 WR or the '87 430 WR is setup to do.

A big part of why the '87 430 WR is faster than the '86 400 WR is that the more substantial damping keeps the front end more stable, and this helps to mitigate the flexy nature of the 40mm conventional forks. The bike still does not have the precise steering control under hard downhill braking that upside down forks deliver, but the '87 430 WR is also not quite the terrifying wet noodle on steep rutted high speed descents that the '86 400 WR is either.

More power, more braking, more damping, more pipe and more muffler. The '87 430 WR also sounds a lot different than the '86 400 WR. The '87 430 WR with the big pipe and big muffler is a lot quieter. It is still pretty loud in the power band, but noticeably more well muffled with it's big muffler than the very loud '86 400 WR with it's skinny little stinger. The really dramatic difference in sound comes at low engine speeds and light engine loads. The '87 430 WR has the same 14/52 stock gearing as the '86 400 WR, and this is the gearing that I have on both bikes. Both bikes had 13/52 gearing on them when I got them, but I went back to the stock 14/52 gearing before ever firing either bike up. The stock 14/52 gearing can seem a bit too tall on the '86 400 WR, but I never considered gearing lower because the bike still only pulls hard up to 82mph at the 6,800RPM top of the power band. That is plenty fast, but it tends to feel very slow compared to the 110mph+ top speed of the 610 four stroke. The '86 400 WR will actually go 90mph with the stock 14/52 gearing, but it gets weak and slow to accelerate past 7,000RPM.

The '87 430 WR does not feel like it is geared too high with the stock 14/52 gearing. Much more substantial torque from 4,000 to 6,000RPM means that taller gears can be carried without the need for clutch slipping in most normal riding. The '87 430 WR also seems to actually go faster up on the top end than the '86 400 WR. The '87 430 WR starts to go flat at a lower engine speed than the '86 400 WR, but the '87 430 does have a broad over rev that delivers substantial power up to higher engine speeds. The power from the '86 400 WR usually just ends right at 7,000RPM, with some weak over rev as high as 7,400RPM on just the right gasoline. The '87 430 WR on the other hand nearly always seems very willing to rev past 7,500RPM.

With more normal gasoline that is neither extremely slow flame front travel speed fuel or spectacularly cold burning gasoline the 1987 Husqvarna 430 WR pulls for quite a while on the top end. The power is dropping off up there, but it keeps pulling and pulling past 8,000RPM. For a two stroke it is quite wide, even compared to many power valve Japanese two strokes the '87 430 WR pulls over a rather wide range of engine speeds.

Again though the really big difference is down low. For power and torque it is the 4,000 to 6,000RPM range of engine speeds where the '87 430 WR is dramatically stronger than the '86 400 WR. Down at 2,500 to 3,500RPM both bikes feel like they have rather similar amounts of torque. The 430 pulls a bit harder way down there at the bottom, but it feels more like just the nine percent displacement difference. The really dramatic difference way down at low engine speeds is in the sound of the bikes. The '86 400 WR tends to crackle and "ring ding ding" a lot down at 2,500 to 3,500RPM, where the '87 430 WR is much quieter and smoother. It gives some rings and dings sometimes, but not nearly to the extent that the '86 400 WR does. The '87 430 WR is also smoother down at 3,000RPM, it pulls much more consistently. Much more four stroke like I might dare to say.

I think the port heights are the same on the '86 400 WR and the '87 430 WR. I have not had the '86 400 motor all the way apart yet to precisely measure the port heights, but I suspect they are the same. Both bikes make peak power at approximately the same 6,500RPM engine speed. The difference seems to be all in the pipe. There is also that little plastic reed block insert for the 250 motor that I am running on the 430 WR, and that may make some small difference. The insert is not really much of a flow restriction as the cross sectional area of the opening at the back of the reed block is still substantially larger than the cross sectional area of the wide open 38mm carburetor. The insert just directs the flow of air and speeds up the velocity of the air hitting reed peddles.

The main difference though in all likelihood is in the pipe. The pipe on the '87 430 WR just has a whole lot more volume out towards the back end. All that volume out at the far end would tend to bolster torque production down at the bottom of the power band, and this is exactly what the '87 430 WR does on a variety of different types of gasoline.

There is also the needle difference in the carburetor. The 6DH20 needle is much more progressive, with a leaner mixture at small 1/4 throttle openings and then a richer mixture up at half and 3/4 throttle openings. This progressive mixture allows more fuel to be dumped in when needed to get the engine to pop off. The '86 400 WR on the other hand has a rich mixture down at 1/4 throttle opening, and twisting the throttle farther does not deliver a richer mixture. The '86 400 WR never needs a big twist of the throttle down at the bottom of the power band. If it won't make power it just won't make power and no amount of aggressive acceleration or big throttle twisting will get it to go. The '87 430 WR is much more four stroke like in that it can usually be coaxed into making torque with some combination of aggressive heavy acceleration to heat the motor up and big twists of the throttle up onto the richer mixture at half throttle.

As far as smooth goes the '87 430 WR certainly does show off it's lighter connecting rod. Over the entire range of engine speeds there is a noticeable lack of vibration when compared to the '86 400 WR. The 330g cut down Mahle piston might help a bit in that regard also. In any case my 1987 Husqvarna 430 WR is buttery smooth.

Despite the 9% larger displacement the '87 430 WR also seems to be able to go somewhat farther on a 3.2 gallon tank of gasoline. Using the meaty midrange from 4,500 to 5,500RPM tends to suck down less gasoline than keeping the '86 400 WR zinging in the 6,200 to 6,800RPM power band all the time.

Smooth and powerful with an almost usably wide power band. If only it didn't smoke like a two stroke. Actually I have had some problems on that point also. Problems with the '87 430 WR not smoking. Several times I have fired it up and it did not smoke at all. When I drained the tank the gasoline was just as clear as from the gas station. The two stroke oil has been mysteriously disappearing over night. It ultimately does not matter much if there is two stroke oil in the fuel or not, carbureted cylinder port two strokes are very dirty engines. They blow lots of unburned fuel out the exhaust. Whether this fuel has oil in it or not it is still a dirty pollution hazard. Very volatile gasoline with no oil in it might not make as much of a mess being blown out the tail pipe of a two stroke, but it is still fuel being blown out all over the place without being burned.

The way to clean up a cylinder port two stroke is with direct injection. With the bulk of the fuel being injected after the exhaust port has closed it can all burn. Any case reed induction engine is going to blow some of the two stroke oil out the exhaust unburned, but even this can be dramatically reduced on a direct injection cylinder port two stroke. The real solution for cylinder port two strokes is to use a two stroke oil that is a clean biodegradable substance. It need not have any particular combustion properties, all it has to do is provide some lubrication of the piston, cylinder and bearings. Direct injection to prevent large amounts of gasoline from being blown out the exhaust unburned and a clean biodegradable oil, such as vegetable oil, that won't do much damage when it is blown out the exhaust unburned. Blowing unburned vegetable oil all over a crowded city with huge numbers of two stroke powered cars and scooters is still not a good idea. A few dirt bikes running around mostly in rural areas is a whole different level of pollution hazard though.

If the substantial sophistication of an electronically controlled direct injection system is being talked about though there are much better types of engines than a case reed induction cylinder port two stroke. Two strokes are not out of the question, in fact a two stroke is still a very good idea for improving transmission efficiency. It does not however need to be a case reed induction two stroke. A roots blower like GM two stroke diesels used or an electric motor driven centrifical blower could make for a very good running two stroke that would have no need for two stroke oil at all as it could use a traditional pressure lubricating system. For simplicity though a high revving short stroke four stroke engine is the way to go. Four stroke gasoline engines have the potential to pull hard and run clean over a wide range of engine speeds from 3,500 to 9,000, 10,000 or even 11,000RPM with any level of fancy electronic gadgetry that might be desired. Especially if it is points and a carburetor that is being used then a four stroke certainly delivers a much wider more usable power band with dramatically lower fuel consumption and much cleaner exhaust than a two stroke. Just so long as that four stroke has a two inch stroke instead of a four inch stroke. A two inch stroke length two stroke can very easily have a much broader and more efficient power band than a four inch stroke length four stroke, and that has been immensely confusing for many people over a long period of time.

Head to Head Comparison: '86 400 Vs. '87 430

It took me a while to get around to doing a head to head comparison of the two big two strokes. On the day that I finally made the effort to do the comparison the gasoline I happened to have was not working very well in either bike. It was a rather fast flame front travel speed gasoline, and the temperature of combustion potential was moderately low. What was really wrong with the gasoline was that it was for higher compression ratio engines. The 12.6:1 '87 430 WR might be equivalent to a four stroke with about a 10.7:1 compression ratio and the 12.3:1 or 12.1:1 '86 400 WR might be equivalent to a four stroke with about a 10.3:1 or 10.5:1 compression ratio. By today's standards those are very low compression ratios, just about every new dirt bike and street bike has compression ratios up above 11.5:1, with 12.8:1 and 13.0:1 compression ratios being very common.

On this high pressure and also somewhat low temperature of combustion potential gasoline the big two strokes were reluctant to get going and tended to fall off the power band all over the place. I have run this type of gasoline in both engines before, so I am pretty familiar with what it will do.

When I started kicking the '87 430 WR on the day of the comparison it was more reluctant to fire up than usual. I kicked and kicked and eventually it started and promptly stalled after about a second. I kicked a few more times and it eventually fired back up only to stall again. This went on for quite a bit of kicking until the motor was finally warmed up enough that it was able to keep running.

When I rode off on the gasoline in the carburetor bowl the '87 430 WR motor was popping off easily down at 4,000RPM and making some pretty good torque. In fact it was lighting off on late compression ignition a bit all the way down to 3,500RPM. At 5,000RPM it was pulling strong and reliably, and the torque was building dramatically to 6,000RPM. Then after I had ridden for about a half mile and the engine was running entirely on the gasoline in the tank it was much different. The torque down at less than 4,500RPM was gone, and even at 4,500 to 5,000RPM it was quite reluctant to get going. The power from 5,000 to 6,000RPM was a bit less than it had been on the gasoline in the carburetor bowl, but it was still giving a pretty good pull once it got going. Then above 6,000RPM the engine was just extremely reluctant to make power and was falling off the power all the time.

With the engine well warmed up and pulling hard in third or fourth gear the motor would keep revving for a long way past 6,000RPM, but it was also often cutting out where it totally stopped making power and would not get going again at all until the engine speed was brought back down to 4,500 to 5,000RPM. The '87 430 WR was pulling way up into the over rev once well warmed up with 7,500RPM being easy to hit and even 8,000RPM was possible, but it was not a useful type of power and I could not get much top speed out of the bike in fifth or sixth gear. The engine was weak with diminishing power above 6,500RPM, but the power was only dropping off rather gradually all the way out to 8,000RPM. The main problem was that it would just fall off the power unexpectedly all the time and it was not fun to ride at all. Down at 4,000RPM there was some torque with a big twist of the throttle, but it was unreliable and reluctant to get going. From 4,500 to 5,500RPM the engine was fairly reliably making torque, but even at that it had to be well warmed up or it just would not pop off. The engine was also unusually harsh at 4,500 to 5,500RPM when it did get going making power. When I shut the motor off it restarted quite easily on the second kick.

After just a short test ride of a few miles I came back and drained the gasoline. I put the gasoline out of the '87 430 WR into the empty tank on the '86 400 WR. The '86 400 WR then would not start up on the gasoline that was in the carburetor bowl. I kicked and kicked but it wouldn't give even one pop. Totally dead. When I drained the gasoline out of the carburetor bowel it was very oily on my fingers. With gasoline out of the tank in the carburetor bowl I kicked the '86 400 WR over a few times and it fired right up easily and continued to run. I didn't even have to take the spark plug out.

As soon as I rode off I could tell that this gasoline was for much higher compression ratio engines. There was just no pop and no power anywhere. No power band at all, just totally dead. Once the motor warmed up a bit I began to get some power at 6,200RPM, but it was hard to get and excruciatingly narrow. Once the engine was fully warmed up after a few miles the power was coming more reliably over the normal 6,200 to 6,800RPM power band, but a lot of the time when I tried to lay down the power it still just would not go. Slipping the clutch got it going a bit more easily, but the power was very narrow and unreliable. The power was ending very abruptly at the 6,800RPM top of the power band with no over rev at all. Down at the bottom of the power band it was also a very abrupt hit without much midrange. The '86 400 WR is always fairly weak in the 5,000 to 6,000RPM range of engine speeds, but it was seeming even weaker than normal at 5,500RPM. Aside from the brutally narrow power band the biggest problem was just that the power was not reliably available. Once the '86 400 WR got going at 6,200RPM it was giving a fairly good feeling pull to 6,800RPM, but even that pull through the narrow power band just was not there every time it was asked for. A few times it even fell off the power band at 6,500RPM after it had started pulling hard at 6,200RPM.

This gasoline might not have been doing very well for dirt bike riding in the low compression ratio two strokes, but it certainly was starting easily. The '86 400 WR restarted very easily after I shut it off. Idle performance was also good in both bikes, neither one stalled while idling in neutral.

To make sure I was doing a fair comparison I swapped the gasoline back into the empty tank on the '87 430 WR and took another short test ride. It was just the same, very unreliable and reluctant to get going with a huge tendency to fall off and totally stop making power anywhere from 5,500 to 7,500RPM.

It is hard to say which of the big two strokes was doing better on this high pressure and somewhat cold burning gasoline. The '86 400 WR was mostly giving a fairly nice pull through it's brutally narrow power band, but it had zero over rev, could never get between the gears in the power without slipping the clutch and the power band was not reliably available even once the bike was well warmed up. The '87 430 WR on the other hand was somewhat more reliably getting going and making power from 4,500 to 6,000RPM but even way down at 5,500RPM it was very annoyingly falling off the power band so frequently that the usable power band was seeming brutally narrow from like 4,800 to 5,400RPM. And even at that the engine was reluctant to get going at any engine speed, including right in the meat of the midrange around 5,000RPM where it is normally quite crisp.

Both bikes felt like they needed higher compression ratios to run this gasoline, although more spark advance would also have done the trick. Each time I have tried adjusting the spark timing on the '86 400 WR it feels like turning the stator does not actually change the spark timing. I always just leave it in the latest spark timing setting. I have not adjusted the spark timing on the '87 430 WR at all, and it looks like no one else has in a very long time either. The stator is very much stuck in one stationary position and I haven't been able to get it to budge.

What is clear from this head to head comparison on the same gasoline is that the '86 400 WR and the '87 430 WR are setup extremely similarly but they do have dramatically different power bands. The '86 400 WR makes power only between 6,200 and 6,800RPM with some small amount of rather weak over rev available on the best gasoline. The '87 430 WR has a gradually ramping up and very usable midrange from 4,000 to 5,000RPM, then the bulk of the power band comes from 5,000 to 6,500RPM with the torque still increasing substantially all the way up to 6,000RPM. Just on the main power bands the '87 430 WR seems to run at a lower engine speed than the '86 400 WR, but that is not the whole story. The '87 430 WR also has an enormously broad and fairly powerful over rev from 6,500 to about 8,000RPM which is very reminiscent of a power valve equipped Japanese two stroke. If engine speeds bellow 6,500RPM were never used it would be easy to call the '87 430 WR the same as a very powerful Japanese 250 two stroke running on race gas. The Japanese 250 two stroke motocross bikes tended to make maximum power at or just above 6,500RPM with a broad powerful over rev out to 8,000RPM, and that is just what the '87 430 WR does on rather weak pump gas. The difference though is that the '87 430 WR also has tons of grunt down to 5,000 and even 4,500RPM. There are Japanese 250 two strokes that make good torque down to 5,000RPM, but nothing like the massive tire churning thrust of the '87 430 WR at 5,000 to 6,000RPM. It is almost like the non-power valve '87 430 WR out power valves the power valve equipped Japanese two strokes. And of course when running on the same gasoline the '87 430 WR will dramatically out pull any 250 two stroke at any engine speed from 4,000 to 8,000RPM. It is after all three quarters more displacement on nearly exactly the same stroke length.

The similarity in 6,500 to 8,000RPM over rev engine speeds seems to be due mostly to the similar stroke lengths. The 74mm (2.91") stroke of the Husqvarna 400/430 motors is really extremely similar to the 72m (2.83") stroke of the Japanese 250 two strokes. It is less than a three percent difference in stroke length. Where the power valve feel of the '87 430 WR comes from is in the wide ports of the over square engine versus the narrow tall ports of the under square Japanese 250 two stroke engines. It is easier to get a wider power band with big broad over rev out of an over square two stroke with wide ports than an under square two stroke with tall and narrow ports. The power valves make up the difference and allow the under square Japanese 250 two strokes to have a broad usable over rev out to 8,000RPM.

To gain a better perspective on the gasoline that had been used in the '86 400 WR and '87 430 WR head to head comparison I also got a fresh can of 91 (RON+MON)/2 octane rating gasoline straight from the gas station. I ran this two gallons of fresh premium in the hot rod 610 motor first to get a good idea of what it was. With 24 degrees BTDC on the static timing setting the 12.5:1 big cam motor was lighting off most easily on late compression ignition down at around 3,700 to 4,000RPM and it was giving a good strong pull up to 6,000RPM with very smooth and quiet operation. It was somewhat slow flame front travel speed gasoline, but it was pulling well with the 250 degree at 1mm valve lift camshaft installed straight up with split overlap right at TDC. The engine was pulling strong and sounding great, but it was requiring a big twist of the throttle to get it going and it would only make power once well warmed up on a big pull. It was able to hit 7,600RPM fairly easily, but there was a lot of cutting out above about 6,000RPM. I bumped the static timing setting up to 28 degrees BTDC, but this made only a rather modest improvement. The engine was certainly much crisper down at 3,200 to 4,000RPM, but even at that it was taking a rather big twist of the throttle to get going. Amazlingly even with 28 degree BTDC spark timing the slow flame front travel speed fuel was working just fine and easily hitting the 15 or 20 degree ATDC latest possible time of late compression ignition from 3,200 to 5,000RPM. Even with all that spark advance the engine was still fairly smooth and quiet from 4,000 to 6,000RPM and it was somewhat more easily and reliably getting going to make the power. The 28 degree BTDC static timing setting also got the engine to pull strong up to over 8,000RPM, but there was still a bit of cutting out sometimes around 6,500 to 7,500RPM.

With a pretty good idea of what this somewhat slow flame front travel speed but reasonably hot burning gasoline was doing in the hot rod 610 motor I drained a half gallon out and put it in the empty tank on the '87 430 WR. I was careful to tip the '87 far over to drain every last bit of the old gasoline out, and then I added the new 91 (RON+MON)/2 octane rating premium gasoline without mixing in any two stroke oil.

When I rode off on the gasoline in the carburetor bowel the 430 motor was lighting off and easily making torque from 4,000 to 6,000RPM even with the engine not yet warmed up. Then once the new 91 (RON+MON)/2 octane rating premium had replaced whatever was in the carburetor bowel the bike just totally fell flat. At first there was absolutely no late compression ignition anywhere and the bike just would not accelerate at all. Then as the motor got fully warmed up it started to pop off from 4,500 to 5,000RPM. It was difficult to get the engine to pop off at all, but once it got going it gave a smooth and powerful pull from 4,500 to about 5,200RPM. I tried a bunch of times but it just would not rev higher. It pulled strong just from 4,500 to 5,200RPM and then completely cut out each time. I could not get any torque down bellow 4,500RPM either. Even with a big twist of the throttle once well warmed up there was just no torque anywhere from 3,500 to 4,500RPM.

When I shut the motor off for a few minutes it was a bit difficult to restart, but it did fire up on about the fourth big kick on that fresh 91 (RON+MON)/2 octane rating premium gasoline. I smeared a few drops of this somewhat slow flame front travel speed gasoline on the top of the tank to see what it would look like. Sure enough it took a long time to evaporate and it left a somewhat oily residue on the black plastic. The motor was not however smoking on this oily gasoline with no two stroke oil in it. I did not notice any smoke at all at low idle or while riding.

I then poured a gallon of the pre-mix that I had been using in the comparison with the '86 400 WR into the tank on top of the half gallon of fresh 91 (RON+MON)/2 octane rating premium gasoline. The pre-mix seemed about the same as it had before, but the bike was pulling somewhat better up to 7,000RPM without falling off of the power band quite so often. Interestingly the engine was even more reluctant to get going at 4,500 to 5,000RPM than it had been on the fresh somewhat slow flame front travel speed 91 (ROM+MON)/2 octane rating premium, but then once it got going it was able to keep pulling to 7,000RPM fairly easily. It was also interesting that the engine was louder and harsher at 4,500 to 5,000RPM even though it was more reluctant to get going and make torque at that engine speed. Obviously the slow flame front travel speed 91 (RON+MON)/2 octane rating premium gasoline had a much higher temperature of combustion potential than the somewhat cold burning but much faster flame front travel speed mystery gasoline.

The big cam 12.5:1 hot rod 610 motor works better on hotter burning gasoline even if it has a somewhat slow flame front travel speed. The '87 430 WR on the other hand works much better on fast flame front travel speed gasoline even if the temperature of combustion potential happens to be substantially low. Clearly the two stroke just does not run as well over a wide range of engine speeds and really needs rather fast flame front travel speed gasoline to rev out well. The big cam hot rod 610 motor on the other hand can deal with somewhat slow flame front travel speed gasoline and still pull hard all the way out to 8,000RPM or higher. Because the big cam 610 motor can run on slower flame front travel speed gasoline it is the dramatically colder burning gasoline that so severely hurts engine performance. The 3.01 inch stroke of the 610 motor and the 2.91 inch stroke of the 430 motor are so close that they are essentially identical. That 3.5% difference in stroke length is just really extremely miniscule, it is only the difference between 7,000 and 7,250RPM at the same mean piston speed. Even though the stroke lengths are essentially identical and the motors run over a similar range of engine speeds from 4,000 to 8,000RPM the two stroke strongly favors gasoline with a rather fast flame front travel speed while the four stroke strongly favors hot burning gasoline.

It also has to be pointed out that a really big problem with this somewhat slow flame front travel speed 91 (RON+MON)/2 octane rating premium gasoline was that it would have required either a higher compression ratio or more spark advance in the '87 430 WR. The same somewhat slow flame front travel speed with the same spark timing would have worked a whole lot better with either a higher compression ratio or a pressure lowering additive in the gasoline. With the spark timing that it was running the 12.6:1 '87 430 WR two stroke just did not have a high enough compression ratio for this particular slow flame front travel speed gasoline. It was very reluctant to get going and make torque at 4,500 to 5,000RPM and it absolutely would not rev up to the 5,500 to 6,000RPM range of engine speeds where the '87 430 WR makes maximum torque.

Port Height

The location and shape of the ports on a cylinder port two stroke is a very important engine parameter. It is analogous to camshaft profile and cam timing on a four stroke, but port timing on a cylinder port two stroke tends to be even more important than camshaft selection and timing on a four stroke just because cylinder port two strokes are so much more difficult to tune.

The ports on the 1987 Husqvarna 430 WR are pretty big and tall, taller than might be expected for an engine that pulls so strong down to 5,000RPM. The center part of the exhaust port on the '87 430 WR is down just 53.8% of the stroke length. At low engine speeds perhaps around 2,000 to 3,000RPM that would be roughly equivalent to a four stroke with an 84 degree ABDC intake valve closing time which would be a massive 308 degree at 1mm valve lift and 110 degree lobe center camshaft installed straight up with split overlap right at top dead center. That seems like a massive amount of duration that would only work up at extremely high engine speeds, and it is true that this exhaust port location does dramatically reduce peak cylinder filling down at low engine speeds around 2,000 to 4,000RPM. There is however a lot more to the way that a cylinder port two stroke runs than just this simple comparison would suggest. First of all it might seem very confusing to be comparing the exhaust port timing on a two stroke to the intake valve closing time on a four stroke. At certain engine speeds though the exhaust port timing on a two stroke and the intake valve closing time on a four stroke are analogous. The intake charge is free to flow out the open exhaust port until the piston has come up to completely close off the entire exhaust port. This is one of the reasons that carbureted two strokes blow so much unburned fuel out the exhaust. The intake ports are lower and close first leaving a portion of the intake charge to be forced out the last part of the open exhaust port as the piston moves up.

There are however a number of other things going on that change the realities of carbureted two stroke operation in significant ways. First of all the ports close off very quickly as the piston moves up through the middle part of the stroke. At the center of the stroke when the crankshaft is near 90 degrees from TDC the piston is moving at it's highest rate of travel. If a port timing value 1mm down from the top of the port is considered this is only about one and a third degrees of crankshaft rotation different than the port timing value when the port is fully closed. What this means is that at cranking and low idling engine speeds the two stroke is able to attain maximum cylinder filling much higher than a four stroke would with a massive 308 degree at 1mm valve lift camshaft. On a four stroke the valves tend to close rather slowly that last half millimeter or so, the last bit of the ramps are gradual so that the valves don't slam closed but instead gently touch down. The '87 430 WR and other similarly high revving two strokes have starting and idling performance like a four stroke with a camshaft much smaller than 308 degrees at 1mm valve lift. For starting and low idling performance the '87 430 WR is equivalent to a four stroke with a 310 degree total duration, which would be somewhere around 250 to 275 degrees at 1mm valve lift depending on how aggressive of a camshaft it happened to be.

So a cylinder port two stroke starts and low idles with gusto, but then becomes very weak over a range of lower engine speeds bellow the power band. Then when a cylinder port two stroke first comes "on the pipe" something entirely different happens. Just going by the 54% exhaust port timing and the 308 degree at 1mm valve lift four stroke camshaft equivalency it would be expected that the engine would really only work best up above about 7,000 or 8,000RPM. The different thing that starts to happen is that exhaust back pressure blocks the exit of some of the intake charge that would otherwise be blown out the exhaust as the piston comes up to fully close off the exhaust port. Constant exhaust back pressure would however also prevent the cylinder from filling with intake air and fuel, so again the way a cylinder port two stroke works is even more complicated. Some small amount of constant back pressure does allow the intake charge to enter while blocking some of that intake charge from being blown out the exhaust port as the piston rises to close the exhaust port off. Another thing that can happen though is a timed reverberation wave that hits the exhaust port just as the piston is moving the last way up from the intake port to the exhaust port. This is where the massively large expansion chamber volume way back near the exit of the pipe on the '87 430 WR comes into play. If it is a fixed length of time that is required for the pressure wave to travel back to the exhaust port then lower engine speeds would require a longer expansion chamber so that the reverberating pressure wave can travel a longer distance over the longer period of time from exhaust port opening to exhaust port closing at lower engine speeds.

Of course just like with a four stroke the engine will make some torque down to lower engine speeds than are ideal for the intake valve closing time. It is a gradual transition from the significantly large amount of the intake charge being forced back out the open intake valve down at low engine speeds to very little of the intake charge being forced back out the open intake valve up where the engine starts to attain peak cylinder filling. It is the same with a two stroke. Even though the 54% exhaust port timing would tend to work best up at above about 7,000RPM the cylinder filling drops off only moderately as the engine speed is decreased down to 6,000 and 5,000RPM. Both the small amount of constant back pressure in the exhaust system and the timed reverberating pressure waves act to prevent the cylinder filling from dropping off as dramatically as might be expected as the engine speed is reduced bellow the 7,000RPM theoretical minimum engine speed for the 54% exhaust port timing. And that is only the exhaust port. The timing of the intake ports are also very significant.

The intake port timing on the 1987 Husqvarna 430 WR is about 77%, that is much lower than where the exhaust port ends. The 77% intake port timing would be approximately equivalent to a four stroke with a 263 degree at 1mm valve lift camshaft with a 106 degree lobe center installed straight up with split overlap at TDC. This intake port timing would tend to work well down to about 5,000 or 6,000RPM, and the '87 430WR does indeed start to make big torque at 5,000RPM with the torque continuing to increase somewhat up to about 6,000RPM. Because of constant back pressure and reverberating pressure waves in the expansion chamber the exhaust port timing tends to be a more gradual and flexible sort of limit on the minimum engine speed. There is no such gradual or flexible nature to the intake port timing though. The intake port timing really is directly comparable to the intake valve closing time on a four stroke. This means that the 77% intake port timing on the '87 430 WR really is like about a 263 degree at 1mm valve lift camshaft in terms of engine performance around 4,000 to 6,000RPM. The cylinder filling is going to significantly drop off at engine speeds bellow 5,000RPM, and even up to 6,000RPM that 77% intake port timing tends to yield higher and higher cylinder filling as the engine speed is increased.

It seems reasonable that both the '86 400 and '87 430 motors have the same port timing. As different as the powerbands are they both seem to fit with these port timing values. The '86 400 starts to build some moderate torque down around 5,000RPM, but then it really takes off at 6,200RPM. This seems to agree well with the 77% intake port timing. The fact that the '87 430 motor starts making big torque at 5,000RPM and continues to make more and more torque up to 6,000RPM also seems to be compatible with the 77% intake port timing. The difference is in the shape of the expansion chambers. The very big pipe on the '87 430 WR with lots of volume out towards the outlet end would tend to do well down to lower engine speeds than the skinny '86 400 WR pipe. It is probably that big fat pipe that allows the '87 430 WR to start significantly building torque from 4,000RPM and then really takes off at 5,000RPM.

It is the 54% exhaust port timing that allows these motors to rev out to 7,000 and even 8,000RPM. The '86 400 WR gets very weak up above 7,000RPM, but it does pull very hard to 6,800RPM and will sometimes make some moderate amount of power out to 7,400RPM. The 7,500 and 8,000RPM performance of the '87 430 WR is also due to that 54% exhaust port timing. The big fat pipe might be tuned for good exhaust scavenging and just the right pressure wave reverberation down at 4,500 to 5,500RPM operation, but the entire exhaust system is large and wide open with a big outlet that will keep flowing up to higher engine speeds. With the rather high 54% exhaust port timing the engine is able to keep revving and making power. The reason that the big two strokes don't make more power up at 7,000 to 8,000RPM is that they just don't flow well enough. At that high engine speed there is not much time for the exhaust to flow out and the intake charge to flow in. It all has to happen very quickly while the ports are open, and that is just not a very large window of time. The ports are huge so that they will flow well, but the 165 degrees of crankshaft rotation that the intake port is open is very short compared to the approximately 230 degrees of crankshaft rotation that the intake valves are substantially open on a four stroke that revs to the same 8,000RPM. And it is actually even worse than this for a cylinder port two stroke. During the last 60 degrees or so of that 165 degree intake port opening time the piston is substantially moving upward. The intake port opening time on a cylinder port two stroke is unavoidably centered around BTDC. That is there is an equal length of time that the intake port is open before bottom dead center and after bottom dead center. The interesting consequence of this is that cylinder port two strokes tend to work best up at extremely high engine speeds in excess of about 8,000RPM regardless of what port timing values are used. No wonder 2.1 inch stroke length 125 dirt bikes made 35hp when 2.83 inch stroke length 250 dirt bikes were only able to do about 43hp.

The very high exhaust port timing is also directly related to why two strokes only attain about 85% of the maximum cylinder filing that a four stroke does. A cylinder port two stroke is sort of like a four inch stroke length push rod drag racing engine with a giant 280 degree at 1mm valve lift camshaft. The dramatically oversize camshaft reduces peak cylinder filling and reduces torque production, but big power to 8,000RPM is what wins races. Down at 5,500 to 6,500RPM the 280 degree at 1mm valve lift camshaft is reducing peak cylinder filling and reducing peak torque production. Then up at above 7,000RPM where the 280 degree at 1mm valve lift camshaft would start to do it's best work the pushrod two valve per cylinder engine just won't flow well enough and peak cylinder filling remains somewhat low.

It is the same thing with the 54% exhaust port timing on the 1987 Husqvarna 430 WR. At all engine speeds bellow about 7,000RPM that very high exhaust port timing is reducing peak cylinder filling. Then up at 7,000 and 8,000RPM where the 54% exhaust port timing would start to work well the cylinder port two stroke just doesn't quite manage to flow well enough to attain really high peak cylinder filling. The two stroke always ends up running down at that approximately 85% peak cylinder filling compared to a strong pulling four stroke.

The '87 430 WR seems to somewhat defy the narrow powerband nature of cylinder port two strokes, but it is still does best over a rather narrow range of engine speeds compared to the Husqvarna 610 four stroke. Cylinder filling on the '87 430 WR is dropping off right from 5,500RPM, and bellow about 4,500RPM cylinder filling begins to drop off much more dramatically. The 610 four stroke retains high enough cylinder filling for some pretty strong torque down to 3,000RPM where the '87 430 WR gets very weak bellow about 4,000RPM. On the other end also the two stroke does not pull nearly as long and strong. Everywhere above about 6,000 or 6,500RPM the '87 430 WR is dropping off. The 610 four stroke on the other hand gets a second wind so to speak at 7,500RPM and gives a very strong additional pull to 8,500RPM. The result is that the 610 four stroke retains extremely high peak cylinder filling everywhere from 4,000 to 8,500RPM with some over rev out to 9,000RPM or even higher depending on the temperature of combustion potential of the gasoline. The '87 430 WR does it's best right in the middle from 5,000 to 6,000RPM and drops off substantially both above and below. The 610 four stroke has a much broader "right in the middle" from 4,000 or 4,500RPM clear through to 8,000 or 8,500RPM and then drops off a small bit both above and below.

For a two stroke though the '87 430 WR is enormously broad in that it actually can pull from 4,000 to 8,000RPM even if it is dropping off considerably for quite a while at both ends. A big question that comes up has to do with how the '87 430 WR can rev to 8,000RPM at all if the spark timing is remaining at the same value all the way through. The answer is that twice as many combustion events heat the engine up more substantially. Any engine heats up as it revs higher and makes more power, but this just happens to a greater extent on a two stroke. Essentially it can be seen as the 430cc two stroke making a similar amount of power to the 577cc four stroke with substantially less displacement. The same amount of power with less displacement means that the engine is going to tend to more easily encounter heat build up and get hot. The heat buildup in a high performance engine tends to increase substantially up at higher engine speeds when the engine gets close to the thermal limit. The closer to the thermal limit an engine gets the faster the heat builds up. What this means is that at high engine speeds a high performance engine tends to just get hotter and hotter. The two stroke more easily gets up close to the thermal limit and tends to keep heating up faster and faster at the highest engine speeds. Because the two stroke heats up more at high engine speeds it is able to stay in late compression ignition mode and continue to make some power even as the cylinder filling is substantially dropping off. It might be said that two strokes are more prone to having over rev both because they have a hard time flowing up at high engine speeds and because they heat up more at high engine speeds which helps prevent them from falling off of late compression ignition.

The 1986 Husqvarna 400 WR does not rev out as high because it is tuned to have a more confined power band. Everything, including the pipe size and shape, works together to deliver high peak cylinder filing within the narrow power band from 6,200 to 6,800RPM. The '86 400 WR probably attains somewhat higher peak cylinder filling than the '87 430 WR does. With a slightly lower 12.1:1 or 12.3:1 compression ratio the '86 400 WR will usually only run right in that narrow 6,200 to 6,800RPM power band where peak cylinder filling occurs. The '86 400 WR probably actually does flow as well as the '87 430 WR up at 7,000 to 8,000RPM but the lower compression ratio prevents it from staying in late compression ignition mode up at those higher engine speeds and it just won't rev out. When the '86 400 WR does rev out to 7,400RPM with weak 35hp power output after a strong 60hp pull from 6,200 to 6,800RPM it is probably a matter of the timing of late compression ignition. With the earlier and easier to hit 5 degree ATDC time of late compression ignition being hit from 6,200 to 6,800RPM the 2.91 inch stroke length engine pulls with authority. Then when the engine falls back down to the latest possible time of late compression ignition at 15 or 20 degrees ATDC the power output at 7,000 to 7,400RPM gets very weak.

The hottest burning race gas might make some substantial power at the latest possible time of late compression ignition all the way up to 7,400RPM, but this does not actually help the '86 400 WR to run over a wider range of engine speeds. With peak cylinder filling occurring at 6,200 to 6,800RPM and substantially diminishing cylinder filling above 7,000RPM it is inevitable that an earlier time of late compression ignition will occur at 6,200 to 6,800RPM than at 7,000 to 7,400RPM. The hottest burning race gas might work fine in the '86 400 WR delivering smooth and powerful torque from 5,000 to 6,500RPM at the latest possible time of late compression ignition, but then the engine is going to tend to fall into full flame front travel mode above 7,000RPM and dramatically loose power. It is just too much of a reduction in peak cylinder filling as the engine speed increases from 6,800 to 7,000RPM. Hotter burning fuel might help some with getting longer and more powerful over rev out of the engine, but the '86 400 WR is just a lot more resistant to revving all the way out to above 7,500RPM than the '87 430 WR whose peak cylinder filling drops off more gradually from 6,500 to 8,000RPM.

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