Lately the History of the Husqvarna Company as an arms manufacturer for the Swedish government going back to the 17th century has been much talked about. Founded in the year 1689 the name was originally spelled Huskvarna and the logo has been called a rifle barrel with sights. The logo is however also representative of a crown, indicating the early business relationship with King Charles the XI of Sweden. By the late 19th century one of the Husqvarna products was bicycles, and in 1903 an imported motor was added to a bicycle frame. The first Husqvarna engine was a side valve (flathead) V-twin produced from 1919 through the 1930's. The first two stroke Husqvarna was a 98cc commuter bike with a two speed transmission introduced in 1935.
The Flathead Husky
The OHV Pushrod Husqvarnas
The Lost Four Stroke
Torsten Hallman and the Rise of the Two Stroke
Cagiva and Ducati
The first motor used on a Husqvarna bicycle was rated at 1/4hp and was supplied by Belgium UN. For 1904 the UN engine was up to a 2hp rating and in 1907 a 3-1/4hp German NSU single cylinder engine was used. The German company NSU had been building bicycles since 1886 and in the early 20th century also produced motorized bicycles. The NSU name comes from the Nekarsulmer Strickmaschinen Union (Knitting Machine Union of Nekarsulm). Nekarsulm being a town on the Nekar River in Southern Germany. NSU much later merged with Auto Union to form Audi. The 3-1/4hp 1907 NSU engine was a type of side valve motor where the intake valve was located directly above the exhaust valve and driven through an external linkage from the bottom of the same camshaft that drove the exhaust valve. This would best be described as a pullrod operated intake valve. In around 1909 the Husqvarna Model 65 was introduced with a 350cc Swiss Moto-Reve V-twin engine rated at 2hp.
These early motorized bicycles were direct drive, with no gear reduction and no selectable ratio transmission of any kind. For a clutch there was just a manually operated variable width front pulley. Some models had no clutch at all. An approximately 4.25:1 total reduction ratio on the belt drive meant that engine speeds were a very low 1,400RPM at the normal 25mph cruising speed.
The name says it all. The Motor she Revs. Well, that's gasoline engines that rev up. Generally speaking anyway. The Swiss Moto-Reve brand gasoline engines, and many other gasoline engines of the first and second decades of the 20th century, used atmospheric intake valves which caused a dramatic lack of power, efficiency and revs.
The usual description of atmospheric intake valve type gasoline engines was that the intake valve was prone to either sticking open or sticking closed. Instead of being opened and closed by a camshaft the intake valve on an atmospheric intake valve engine just rides on a spring. When the piston moves down on the intake stroke the intake charge is sucked through the intake valve and the flow of air pushes the valve open. The obvious problem with this arrangement is that it causes a significant pressure differential between the atmosphere side of the intake valve and the combustion chamber side of the intake valve. The stiffer the spring the larger this pressure differential. The spring loaded atmospheric intake valve is essentially a pressure regulator. The pressure setting is proportional to the amount that the intake valve opens. The minimum pressure differential across the intake valve is determined by the seat pressure of the atmospheric intake valve. If the atmospheric intake valve spring is short with little or no pre-load then the force required to open the intake valve increases considerably as the intake valve is opened farther. A long intake valve spring with a free length of more than about five times the required intake valve lift with a substantial 30% or more pre-load maintains a fairly constant spring pressure across all valve lift amounts. With a long spring and sufficient spring pre-load the pressure differential across the intake valve is much closer to the spring pre-load setting.
Even with a very long intake valve spring setup with a minimum of seat pressure atmospheric intake valve engines are weak poor performers. Before the flow of intake air can begin a pressure differential has to be established to accelerate the intake valve open. Then at the end of the intake event there is another delay after the intake charge stops flowing into the cylinder before the intake valve actually closes to prevent backflow out of the cylinder. The result of all of these difficulties is that atmospheric intake valve engines are ill-suited for use at the elevated engine speeds where gasoline engines work well.
As far as the history of motorcycles goes the result of the widespread use of engines with atmospheric intake valves was that the engine displacement was made very large to get the bike to move under it's own power. The combination of a pathetic engine and little or nothing in the way of selectable drive ratios meant that motorcycles of the first two decades of the 20th century were pretty poor performers. Huge 250cc to 500cc engine displacements resulted in rather large amounts of torque production potential, but both hill climbing ability and top speed were less than stellar despite correspondingly huge gasoline consumption rates.
In 1913 the Moto-Reve motors were actually overhead valve engines with both the intake and exhaust valves in the cylinder head driven by external pushrods and external rocker arms. This was a parallel valve OHV engine. It is not clear how many 1913 Husqvarna Model 65 motorcycles were built with the V-twin OHV motors. What is clear though is that this was a big change from the earlier atmospheric intake valve Moto-Reve motors
The 1914 and 1915 404cc V-twin Moto-Reve motors that were used on Husqvarna motorcycles also had camshaft driven intake valves, but it was in the old pullrod style of the 1907 NSU motor with the intake valve directly above the exhaust valve in a side valve arrangement. A decidedly old fashioned valve train arrangement compared to the 1913 OHV V-twin motor.
Another significant upgrade for the 1914 and 1915 models was a Swiss made Moto-Reve two speed transmission. The transmission not only provided two selectable ratios, but also allowed a much larger amount of overall reduction for better performance at low speeds and on steep hills.
In 1916 Husqvarna introduced their own three speed gear box mated to a 548cc Moto-Reve V-twin rated at 4hp. This was the beginning of real motorcycle production at Husqvarna, but the partnership with Moto-Reve soon fell apart and development began on a Husqvarna motor.
The first Husqvarna motor was the 1919 side valve 550cc air cooled V-twin with both valves in the cylinder block. A true flathead. This was a big improvement over the atmospheric intake valve Moto-Reve engines in that power output was dramatically increased with roughly the same engine displacement. The result was a rather fast motorcycle that could both climb steep hills and attain scary fast top speeds.
What the flathead motors also did though was run dirty with higher unburned hydrocarbon emissions. At the time this was somewhat glossed over simply because the improvement in performance and efficiency over atmospheric intake valve engines was so dramatic and so obvious. Regardless of the location of the valves, in the cylinder head or upside down in the cylinder block, driving both the exhaust and intake valves with a camshaft resulted in a much wider range of operable engine speeds and sufficiently high engine speeds were easily attainable to run in late compression ignition mode up at above 3,000RPM. Problems surrounding poor flow and an inability to easily attain compression ratios above about 9:1 seemed like relatively minor concerns compared to the dramatic improvement in performance and efficiency over the atmospheric intake valve engines.
In 1922 a 990cc flathead V-twin engine was also introduced. This larger displacement Husqvarna flathead was considered a sidecar engine, but the same bike was available just as a 990cc motorcycle. Through the 1920's and 1930's these flathead motors were the staple of Husqvarna motorcycle sales. By the mid 1920's though development was turning towards a new type of Husqvarna motor.
The first overhead valve Husqvarna motor was a 500cc V-twin canted valve pushrod race engine developed sometime in the 1920's. Extensive use of aluminum for the engine and transmission cases on 500cc OHV road race bikes of the 1920's and 1930's lowered the overall bike weight and Husqvarna saw significant success in TT and Grand Prix racing in Europe. A cut down single cylinder version of the same engine was also raced in lower displacement classes. Single cylinder canted valve pushrod production engines also were offered in the late 1920's alongside the more popular V-twin flatheads.
In 1930 there were 175cc, 248cc and 496cc single cylinder flatheads as well as the 550cc flathead V-twin. Alongside these base models, OHV engines were also offered for a significantly higher purchase price. The 248cc single cylinder OHV Husqvarna of 1930 had a retail price 19% higher than the 248cc flathead. Likewise the 491cc OHV single cylinder Husqvarna retailed for as much as 35% more than the 496cc flathead single cylinder Husqvarna. These push-rod canted valve OHV engines were a significant performance upgrade over the flathead models, but the higher price and a general lack of knowledge on the part of buyers about the disadvantages of side valve motors resulted in small sales volumes.
An interesting feature of the 1930 Husqvarna models was that the OHV and flathead engines did not share the same bore and stroke dimensions. The 248cc flathead single had a 2.54 inch bore and a 2.99 inch stroke, the 248cc OHV single on the other hand had a 2.46 inch bore and a 3.15 inch stroke length. A small but significant difference. The bigger 500 class single cylinder engines had an even more dramatic difference in stroke length, but this time it was the other way around with the OHV engine having the shorter stroke length. The 1930 Model 50 491cc OHV single had a square configuration with a 3.37 inch bore and a 3.35 inch stroke length. The 1930 Model 50S 496cc flathead single had a significantly under square configuration with a 3.11 inch bore and a 3.98 inch stroke length. Obviously the shorter stroke OHV engine would have had dramatically more performance potential. The output ratings were 14hp for the 496cc flathead and 25hp for the 491cc OHV engine, and these are obviously very conservative ratings for extremely mildly tuned stock engines with very low compression ratios. The OHV 248cc single had an output rating of 11hp with a 5.6:1 compression ratio where the 1930 through 1934 248cc flathead had an output rating of just 7.5hp at 4,000RPM with it's slightly shorter stroke length. A "Specialracer" version of the 491cc OHV single with the cylinder tilted forward at a 30 degree angle was also offered in 1930. This "Specialracer" had a large inch and a half diameter header pipe with no muffler and was rated at 33hp.
A significant change for 1933 was that the regular models of the big 500 single were built with the cylinder tilted forward in the style of the 1930 "Special Racer". The smaller 348cc singles retained the vertical cylinder, presumably because the lower power output of the small motor benefited from more weight on the rear wheel for better drive traction in the mud and snow.
From 1934 to 1936 flatheads and OHV engines were again offered as competing models. The small single cylinder Husqvarna was up to 348cc and both the flathead and the OHV engine shared the same 2.80 inch bore and 3.46 inch stroke length with output ratings of 9hp at 4,000RPM and 14hp at 4,500RPM respectively. For 1934 the price difference was up to a 23% premium for the OHV motor, a seemingly irrationally high price premium just for the OHV valve train on the same basic motor in the same bike. Somehow the 1934 through 1936 OHV 348 Husqvarna managed to weigh 140kg to the 120kg of the 1934 to 1936 flathead 348, again an unexpectedly large increase in weight just for the OHV valve train on the same bike.
The reality though was that the bikes were not exactly the same. The OHV 348 had larger drum brakes, a larger 12 liter gas tank to the 10 liter tank of the flathead 348 and the OHV model also had a completely different 3 speed transmission with tighter spacing between the gears. The flathead 348 had 55% jumps between the gears, the 1934 OHV 348 on the other hand had a similar 57% jump between 1st and 2nd with a much tighter 65% jump between 3rd and 4th for better high speed performance. In 1935 the gas tank on the flathead was increased to 11 liters but otherwise the 348cc Husqvarna models were mostly unchanged from 1934 to 1936. In 1935 the price premium for the OHV 348 model went up to 27%, but then dropped to 13% for 1936.
From 1934 to 1936 the big 496cc singles also shared the same bore of 3.11 inches and the same stroke length of 3.98 inches for both the flahead and the OHV model. For 1934 and 1935 power output on the 496cc flathead single was the same 14hp at 3,900RPM as previous years, but the new 496cc OHV single was down to 22hp at 4,200RPM from the 25hp of the substantially shorter stroke length 491cc previous model. For 1934 and 1935 the flathead weighed 155kg and the big OHV single weighed 165kg. The price premium was 27% for the 1934 496cc OHV model. For this much higher price and modest 6% higher overall weight the OHV model got a close ratio four speed transmission with a 63% jump between 1st and 2nd, a 74% jump between 2nd and 3rd and a rather tight 80% jump between 3rd and 4th. For 1935 the 496cc models were mostly unchanged, but the price premium for the OHV model did drop all the way down to just 9%.
For 1936 power output for the 496cc flathead single was up slightly to 15hp at 4,200RPM but power output for the 496cc OHV single was up substantially to 24hp at 4,000RPM and both bikes also got new four speed transmissions. The 1936 flathead 496 got a four speed with an even spread of ratios, a 65% jump between 1st and 2nd, a 75% jump between 2nd and 3rd and a 78% jump between 3rd and 4th. The 1936 OHV 496 used a different four speed transmission with similar ratios, a 64% jump between 1st and 2nd, a 75% jump between 2nd and 3rd and a 79% jump between 3rd and fourth. The price premium for the 1936 496cc OHV model remained down at 8%, the weight of the OHV and flathead 496 models was also the same 155kg for 1936.
In 1930 the only production V-twin models were the 15hp 550cc Model 190 with a 3.27 inch stroke length and the 16hp 598cc Model 61 sidecar with a 3.98 inch stroke length. For 1932 the 3.98 inch stroke length 990cc V-twin flathead was back with an output rating of 26hp at 3,500RPM and the bike weighed 195kg without a sidecar.
In the late 1950's Husqvarna was again a major player in European racing, this time though it was off road racing on dirt bikes. The bike was a modern dirt bike of the time with telescopic forks and dual shock rear suspension. The motor was an updated version of the old Husqvarna 500cc air cooled single cylinder OHV canted valve engine, once again installed with a vertical cylinder for better drive traction in the mud. Husqvarna was not the only manufacturer in the game in Europe either. Similar long stroke length 500cc OHV singles were produced by a variety of other manufacturers around the same time.
All of these European 500 class four strokes did however have one large and significant shared problem. The stroke lengths were way too long. With stroke lengths in excess of three and a half inches the motors were torque monsters that required hot burning gasoline and careful tuning to rev out far enough to run over a wide range of engine speeds. It was not that they were not fast, they certainly were capable of making some big power in the hands of a top racer. With two large canted valves on a big aggressive roller camshaft the under square engines were capable of flowing well over a rather wide range of engine speeds. Way back in 1935 the Husqvarna Grand Prix race bike with a similar 500cc pushrod engine and a shorter three inch stroke was said to produce 44hp at 6,800RPM with a 10.0:1 compression ratio. The big problem with the 1950's singles was that they just did not run all that well with the extremely excessively long stroke length. They were not practical for most purposes, and even for all out racing the long stroke engines were difficult to tune and tended to have poor power delivery.
The other problem was that even from a 500cc single cylinder engine with a three and a half inch stroke length the amount of power was more than the chassis of the time could well handle. The suspension and brakes just were not up to the task of going that fast. Top riders were able to cover ground rapidly, but it was an exhibition of speed, strength and luck more than it was real racing or practical transportation.
Another significant manufacturer of 500cc four stroke singles in the 1950's was BSA. With Husqvarna focusing on cheap high profit two stroke scooters through the late 1940's and into the 1950's demand for cleaner and more efficient four strokes was met by other European manufacturers. The BSA Gold Star 350cc and 500cc air cooled singles had been introduced in 1938 and production was resumed a few years after the end of WWII. The BSA single was also a pushrod canted valve engine, but it was considerably different from the Husqvarna pushrod engines in that BSA located the pushrods on the back of the engine near the intake as in the 1913 Moto-Reve OHV parallel valve engine. To drive canted valves off of intake located pushrods a complex multi-stage linkage system was used. In typical BSA fashion the system worked like clockwork, but the additional heavy linkage limited the range of engine speeds where high cylinder filling could be attained even compared to other pushrod engines. The pushrod Husqvarnas on the other hand used side mounted short throw pushrods on roller lifters that drove a single set of ratio rockers.
In any configuration pushrods result in a heavy valve train that can easily run into reliability problems when aggressive camshafts are used at high engine speeds. The advantages of an overhead camshaft engine are unmistakable and the general drive in that direction was happening all around Husqvarna Motorcycles in the 1950's. Bill Nilsson had won the inaugural F.I.M world 500cc motocross championship in 1957 as a privateer on a British AJS 7R road racer which he had modified himself for use in the dirt. The AJS 7R was a 350cc SOHC canted valve single which Bill Nilsson had taken out to 420cc to run in the 500cc class. Bill Nilsson went on to win the F.I.M. 500cc world championship again in 1960 on a pushrod Husqvarna, but the writing was on the wall. Pushrods were yesterdays news.
Husqvarna factory racers won the F.I.M motocross world championship again in 1962 and 1963 with the same long stroke pushrod engines, but that was the last of it. Husqvarna dropped the four stroke entirely after 1963. The 1962 and 1963 500cc world champion Rolf Tibblin was however not done with four strokes. Former Husqvarna factory race mechanic Nisse Hedlund also believed in the four stroke and had started his own company to build and race a similar long stroke 500cc single. Rolf Tibblin raced for Hedlund in 1964 and came up one broken front wheel short on the last lap of the last race of the series and settled for second to Jeff Smith riding for BSA factory racing. Jeff Smith successfully defended his F.I.M 500cc world motocross title in 1965 on a 441cc BSA C15 OHV single with the pushrods on the side as in the Husqvarna pushrod engines, but that was the end for four strokes. After 1965 there were no four strokes available that could compete with the new big bore two strokes from CZ, Maico and Husqvarna.
For 1966 BSA poured enormous amounts of cash into a custom titanium four stroke, but Jeff Smith came in third in the points standings behind Rolf Tibblin and Paul Friedrichs on cheap two stroke CZ race bikes. Not only was the frame all titanum on Jeff Smith's 1966 race bike, but much of the engine incuding the connecting rod was hand machined out of solid blocks of titanium. Despite all the expensive custom titanium parts the motor was still the same long stroke length pushrod engine. Again in 1967 Jeff Smith had some sucess on the titanium BSA, and in 1968 and 1969 John Banks managed second place finishes in the F.I.M 500cc world motocross championship. In 1968 Banks came up behind Paul Friedrichs on a CZ and in 1969 it was Bengt Aberg on a two stroke Husqvarna that came out on top. BSA was unwilling to build a new big bore four stroke platform when the old long stroke pushrod engine was turning in fairly competitive results. The C15 platform BSA was using for the titanium four stroke was based on the old 1952 150cc Triumph Terrier first expanded out to the 200cc Triumph Cub and then out to the 250cc BSA C15 for 1958. The C15 engine was fairly well maxed out at 441cc with a 3.11 inch bore on a lengthended 3.54 inch stroke.
In 1972 BSA went out of buisness and John Banks was left to campain left over junk BSA parts, which he did fairly competitively for many years with the help first of Eric Cheney and later Allan Clews. The last BSA factory development in 1971 was the new B50 engine with a larger cylinder head and wider spacing between the valves. This bigger cylinder head on a 3.31 inch bore with the same 3.54 inch stroke length yielded a 499cc displacment. Those 3.31 and 3.54 numbers might ring a bell for someone familiar with the early Chrisler Hemi automotive engines. It was this larger bore B50 engine that John Banks and Allan Clews campained throughout the 1970's against the increasingly powerfull two strokes. The B50 was however still an undersquare engine with too long of a long stroke length to be able to attain high efficiency or make big power over a wide range of engine speeds. The next time a four stroke would top the F.I.M 500cc motocross world championship standings it would be Jacky Martens in 1993 on a Husqvarna TC610 de-stroked to a 2.60" stroke length.
As early as 1957 a new breed of dirt bike was on the rise. Husqvarna had been producing some small two stroke motorcycles as far back as 1935, but they had been more about simplicity and ease of manufacture than about any kind of performance. The German DKW 125 two stroke of the 1930's was legendary for it's high power output, and in the late 1940's after the end of WWII both Husqvarna and Harley Davidson jumped on the two stroke bandwagon to produce cheap high performance and high profit motorcycles that appealed to young novice riders. DKW is by the way an uproariously funny name for a manufacturer of lightweight high performance motorcycles: Dampfkraftwagen means Steam Powered Vehicle in German. Wirklisch ein Dampfer? Sei trozdem immer tapfer und vergiss nicht den Daempfer.
Already by the late 1950's two strokes were beginning to have some racing success against the four stroke race machines. The big shift came around 1961 when Torsten Hallman began going very fast on a 250cc two stroke. A shorter stroke length allowed for higher peak power production potential, but it was mostly the new generation of lightweight dirt bike chassis with longer travel suspension that made the difference. The big heavy long stroke length four stroke with next to no suspension was no longer competitive and lost popularity. Several Swedish and British manufacturers continued on building the big four stroke singles into the late 1960's, but Husqvarna completely switched to two stroke racing. When the 500cc four stroke was dropped after 1963 it was replaced by a new lightweight 400cc Husqvarna two stroke in 1964. For very nearly 20 years Husqvarna produced nothing but air cooled cylinder port two stroke dirt bikes. Despite the rise of stiff Japanese competition in the late 1960's and throughout the 1970's the classic Husqvarna 250, 360 and 400 two strokes continued to be king of the heap. It is this era that is most talked about, but it was really just a side note in the history of Husqvarna Motorcycles.
One of the interesting stories from this period comes from Torsten Hallman himself. After wining four world championships on Husqvarna 250 two strokes the entire Husqvarna motorcycle operation seemed about to collapse around 1969. Sales of the highly specialized motocross two strokes were small compared to Husqvarna's other consumer products. Husqvarna was apparently a rather large corporation and the motorcycle division was so small as to be in danger of losing money. As Torsten Hallman put it he was told that there might not be a next year of production, but personal friends within the Husqvarna Corporation were said to have gotten some money allocated to run production for one more year so that he (Hallman) would have a bike to race.
As it turned out production of the two stroke race bikes did continue year after year but development stagnated and Torsten Hallman left to race for the Japanese. Despite minimal development and improvement Husqvarna did continue to win races into the late 1970's with factory sponsored racers as diverse as Heikki Mikkola, Californian Brad Lackey and Hakan Carlqvist. All three of these riders later went on to win F.I.M 500cc world championships on Japanese two strokes. Heikki Mikkola for Yamaha in 1978, Brad Lackey for Suzuki in 1982 and Hakan Carlqvist also for Yamaha in 1983.
Under Electrolux corporate ownership Husqvarna Motorcycles once again became a dynamic and significant operation. Innovation was slow at first, but some significant new models were introduced in the early 1980's. The first big innovation was the 1984 Husqvarna 510 four stroke introduced as a late 1983 model. The new four stroke was based on the existing two stroke bottom end and transmission, but it did require all new cases to accommodate the larger bore diameter and cam chain. It was however really still the same engine layout as the two stroke with interchangeable primary reduction, clutch and transmission parts. The same spacing between the crankshaft and the transmission main shaft was used, and this set the maximum stroke length of the engine. That existing layout was really a 500cc two stroke bottom end, with just enough room for the 84mm stroke length of the 488cc Husqvarna 500 CR to fit. The stroke length of the new four stroke was reduced slightly to 76.5mm to make room for the larger 38mm big end bore and 30mm crankpin. It's the biggest four stroke bottom end that would fit in the existing two stroke engine layout. Why so big? Obviously to compete directly with the 500 two strokes. The 503cc displacement of the new 510 four stroke was not enough to make the same big power as the 488cc Husqvarna 500 CR two stroke, but it was actually not all that far off on peak power and the broader power of the four stroke was of course an enormous advantage for all types of racing.
There is actually about 0.22" of clearance between the connecting rod big end shell and the divider between the crankcase and the gear case and an even more substantial 0.27" of clearance out to the rest of the crankcase with the 3.01" (76.5mm) stroke length and the 38mm connecting rod big end bore. A slightly longer stroke length would actually fit. If the big end bore were increased proportional to the stroke length increase a 3.25" (82.5mm) stroke length with a 41mm connecting rod big end bore would just fit in the cases with hardly any clearance between the outside of the rod shell and the divider between the gear case and the crankcase. The reality though is that going this big might not be practical. As stroke lengths are increased beyond about 2.5 inches on gasoline engines loads on bearings increase disproportionately to those stroke length increases. A 3.25" stroke gasoline engine might actually need more than a 41mm big end bore to work reliably. Then there is also the issue of oil flow away from the rod shell, near zero clearance would result in dramatically higher frictional losses from the rod pushing the oil out of the way at high engine speeds. Some amount of clearance between the connecting rod and the cases is required to maintain high efficiency.
That 0.22" of clearance is however very substantial, so some small stroke length increase would in fact be practical. A 3.15" (80mm) stroke length on a 40mm big end bore would leave a still rather substantial 1/8" clearance between the rod shell and the divider. The 3.15" stroke probably could be made to work just fine, but it would be an increase in displacement from 503cc to just 526cc on the 91.5mm bore of the original Husqvarna 510 motor and it certainly would come at the expense of some small reduction in efficiency.
The new four stroke Husqvarna was reminiscent of the late 1920's through early 1960's 500cc OHV Husqvarna four strokes in that it was still an air cooled 500cc canted valve single. The 1984 Husqvarna 510 was however built as a four valve per cylinder engine in the style of the four valve per cylinder Honda dirt bikes of the time. The early four valve Hondas were the 1978 and 1979 Honda XL250S, the 1981 and 1982 Honda XR250 and the 1979 through 1982 Honda XR500 which were all SOHC four valve per cylinder engines with the intake valves parallel to each other and the exhaust valves parallel to each other. The RFVC Honda XR350 and RFVC Honda XR500 introduced in 1983 and the RFVC Honda XR250 introduced in 1984 are considerably different with their complex and heavy two stage rocker system also driven by a single overhead camshaft. Someone at Honda around 1982 must have been a BSA fan, what with all of those rockers. Yamaha jumped on the four valve per cylinder bandwagon as well in 1984 with the introduction of the air cooled DOHC XT600, the old Yamaha XT500 had been a more traditional air cooled SOHC two valver.
This was a milestone decision to go with a four valve per cylinder configuration, both on the part of Honda in 1978 and on the part of Husqvarna and Yamaha around 1983. The significance of this is seen in the next big innovation at Husqvarna, the introduction of the water cooled 1984 Husqvarna 250 CR two stroke. The two stroke benefited significantly from water cooling, but the impetus probably came from testing of the high performance air cooled four valve per cylinder four stroke. Air cooled four strokes work fine with moderate power output levels, especially with just two valves per cylinder which leaves much more room on the cylinder head for the heat to actually get out to cool the motor. A four valve per cylinder four stroke without water cooling would best be described as an "un-cooled" motor. There is just nowhere for all that heat to go with the cylinder head chock full of intake and exhaust valves. Unsurprisingly power output from the air cooled Japanese four valve dirt bikes was generally considered excessively weak.
Other significant innovations at Husqvarna included a box section aluminum swing arm for 1985 and a disk front brake for 1986. That was pretty much it for Electrolux innovation. In 1987 the motorcycle division was sold to the Italians and a whole new chapter of Husqvarna history began.
Brothers Claudio and Giafranco Castiglioni owned a metal pipe company and small parts manufacturer founded in 1950 by their father Giovanni Castiglioni in Varese, Italy. In 1978 the Castiglioni brothers purchased the old Harley-Davidson Aermacchi factory and went into business manufacturing, racing and selling updated versions of the old Aermacchi built Harley-Davidson horizontal cylinder air cooled motorcycles.
The old 1960's Aermacchi Harley-Davidson 250 and 350 models have their own interesting little stroke length fiasco story, and it ends up being very relevant to later Italian Husqvarna models in a roundabout sort of way. See Connecting Rod Big End Bearing Diameter and Engine Stroke for more on the Sprint 250.
Cagiva rather quickly scrapped the entire Sprint 250 and Sprint 350 platform and switched to developing and racing small high performance two strokes. They had success in racing and sales in the early 1980's and went on a buying spree purchasing Ducati in 1985 and two years later Husqvarna.
The first big thing that happened with the 1987 purchase of Husqvarna Motorcycles by Cagiva was the introduction of a water cooled four stroke Husqvarna. This innovation was however so quick that it is likely most of the development work was actually already complete before Cagiva took over. The water cooled 1987 Husqvarna 510 four stroke was a big change, and the changes were not isolated to the radiators, water pump and cooling jackets. All of the 1987 models also got twin piston Brembo front calipers and most 1987 models received the White Power 40mm upside down forks. Only the Enduro models retained the classic old 40mm conventional Husqvarna forks.
That first year under Cagiva ownership in 1987 was reif with changes. The 1987 plastic, including the gas tank, was made by Acerbis in Italy and the rear suspension received an all new linkage system. For 1988 and 1989 though the Italian made Husqvarna models remained nearly identical to the 1987 model. The big changes were being saved up for an anti-climax of sorts in 1990.
For 1988 there was one significant change. The old Husqvarna 125 two stroke was dropped from the model line and in it's place the 1987 Cagiva WMX 125 two stroke was rebadged as a 1988 Husqvarna 125. The reason for this move is obvious, the old Husqvarna 125 was in the same cases with the same transmission as the Husqvarna 400,430 and 500 two strokes. The Cagiva 125 two stroke was a lighter bike, and the power valve type 125 two stroke motor had been the main focus of Cagiva development through the mid 1980's. Cagiva had even won the 1985 F.I.M. 125cc motocross world championship with Finland's Pekka Vehkonen.
For the 1990 model year the rest of the old Husqvarna two strokes were also dropped, and in their place were 125, 240, 250 and 260cc Cagiva derived power valve two strokes.
The really big thing for the 1990 model year though was a big bore kit on the water cooled Husqvarna four stroke. With displacement up to 577cc the open class thumper was able to turn in some serious thumping indeed. The anti-climax was that the 1990 four stroke models apparently were not ready in time or did not sell. Hardly any 1990 Husqvarna 610 bikes seem to exist, and some of the 1990 Husqvarna 610 bikes received a new VIN number and were sold new in 1991 through some mysterious work of trickery. It was only the new Husqvarna WMX 610 that was introduced in 1990, the very similar Husqvarna WXE 610 and the Husqvarna WXE 350 were first sold for the 1991 model year. So 1991 was really the first year of the new models, but again production volumes were not large and sales were rather low.
The new 1990/1991 four stroke models also got a disk rear brake, a larger 240mm front rotor, a White Power rear shock, a new rear sub frame and all new plastic with a smaller 2.40 gallon Acerbis gas tank. With this new plastic, White Power suspension and Brembo brakes the 1991 four strokes looked much like the Cagiva derived 1991 two strokes, but it was on the outside only. Under the skin the 1990/1991 Husqvarna 610 four stroke was the same old Swedish bike, with the same engine cases, the same cylinder head, the same transmission and in the exact same frame as the 1983 through 1989 Husqvarna 510 four stroke. Some of the old 1987-1989 water cooled Husqvarna 510 four strokes with drum rear brakes were also sold new in 1990 as 1990 models, so there actually were both 510 and 610 four strokes for the 1990 model year. Apparently none of them sold well in 1990 or 1991.
In Europe there were new Husqvarna derived Cagiva models as well. Most notably an air cooled SOHC four valve 601cc four stroke single with a larger 102mm bore size and a shortened 73.6mm stroke. This motor was obviously built on the same Husqvarna 510 four stroke platform. The water cooled 610 model was brought out to only a 98mm bore because there needed to be room for the cooling passages between the cylinder liner and the head bolts. With the same head bolt spacing though an air cooled version was easily able to go out to a 102mm bore size. If the original 76.5mm stroke length of the 1983 Swedish 510 was kept this new 102mm bore would have yielded a 625cc displacement. Instead the new Cagiva W16 model was de-stroked to a 601cc displacement. This air cooled model was in a Cagiva frame and it really was a completely different motorcycle with electric start and a left side chain, it just shared the same basic engine architecture and dimensions of the Swedish 510 four stroke. Later a water cooled 577cc Cagiva four stroke that looks exactly like a Husqvarna 610 was also released. Both of these European Cagiva four stroke singles were sold new with full lighting, mirrors, speedometers and quiet mufflers for street use.
It is not clear exactly what happened, but it seems likely that the lack of profitability of the 1990 and 1991 Husqvarna models spurred cost cutting measures for the 1992 model. The dramatic changes for 1992 may also have been due to shifts in availability of components from European suppliers such as White Power. In any case the 1992 models got Japanese Showa forks and shocks and Japanese Nissin brakes. Both big steps backwards for the otherwise iconic Husqvarna models. Another significant cost cutting measure for the 1992 Husqvarna four strokes was the introduction of a new clutch and clutch cover. The main cost cutting measure here was that the old one piece cast steel clutch basket and primary reduction gear was discontinued. In it's place was a much cheaper to produced riveted on aluminum clutch basket. The new 1992 clutch works well, it can even be seen as an upgrade over the old 1991 clutch in that it has a larger diameter with more capacity and works very smoothly and consistently at least when the aluminum basket is new and in good condition. The problem is that an aluminum clutch basket does not last all that well. In a rather short period of time the aluminum basket wears and clutch feel deteriorates. Overall the 1992 clutch is slightly heavier than the all steel clutch it replaced, and the new two piece clutch cover is much more prone to damage and oil leaks than the old one piece clutch cover.
The 1992 Nissin brakes aren't really all that bad. With the correct pads the 260mm oversize front disk works fine. The feel at the lever is a bit strange and touchy while also requiring more force with the fingers, but it is not really all that bad. Just different. The 1992 Nissin rear brake appears to work perfectly. The real problem with the 1992 Japanese cost cutting measures is the Showa suspension. It just does not belong on a Husqvarna. Well, it really does not belong on anything with wheels. On a dirt bike it is horrendously harsh while also managing to be very slow over most types of terrain. What it comes down to is that the Showa suspension is simply missing volume dependant damping circuits, and this is a significant oversight.
The 1992 Showa suspension downgrade seems to have been the demise of the Italian Husqvarnas. For a decade development and innovation ground to a halt. Some different forks were tried, including a big heavy conventional Showa fork and a Marzocchi 40mm upside down fork, and eventually an additional high speed compression clicker was added to the Showa shock. The lack of separate high and low speed compression damping was however not the problem with the Showa suspension. Changing the proportion of high and low speed compression damping results in the bike either being even harsher or even slower. More low speed compression damping and the suspension won't compress over normal medium size and flowing bumps. More high speed compression damping and the suspension won't absorb small sharp bumps like rocks and roots. Backing off on either the high speed or low speed compression damping makes the suspension more prone to excessively easily bottoming. The Showa suspension is simply lacking any sort of volume dependant compression damping that can absorb the big falling out of the sky impacts without compromising speed and comfort with the tires in contact with the ground. Normal a dirt bike begins powerfully absorbing the energy of a landing shortly after the tire touches down. The White Power suspension on the 1991 Husqvarna WMX 610 also appears to have a top out feature that cancels the volume dependant damping when the suspension fully extends. Instead of the suspension compressing several inches before the volume dependant compression damping engages the stiff compression damping just starts right from the first instant the rear tire touches down. It is mostly the 1991 White Power shock that exhibits this large energy absorbing capability on big landings while also remaining soft, compliant and comfortable in normal riding. The 1991 White Power 40mm forks also seem to have substantial volume dependant compression damping but any top out feature is less pronounced. Because the front end tends to ride high in the stroke in many conditions the compression damping needs to stay soft and compliant on small bumps all the way up to near the top.
The 1992 Showa suspension does not do this. When landing from a jump the 1992 Showa suspension simply blows through the stroke at both ends and does not absorb enough of the energy of the impact. Instead it is just a big clank at the bottom telling the rider not to do that again. Turning the compression clickers in will absorb more of the energy of a big landing, but then the bike gets even more uncomfortable and slower. The compression clickers on the 1992 Showa suspension seem to mostly adjust the low speed compression damping. Turning the clickers all the way in does help a bit with absorbing all types of impacts, but then the suspension becomes very immobile and just does not seem to be moving at all in normal riding. The 1992 Showa suspension simply does not work for anything other than a smooth groomed track with timed landings and smooth bumps small enough to not severely bottom the suspension. In the real world the 1992 Showa suspension is uncomfortably harsh on rough pavement and most dirt roads and will bottom out extremely easily when crossing ditches or any sort of a flat landing from a bump or jump bigger than a parking lot speed bump. The saving grace of the 1992 Showa suspension is that even if it is slow and uncomfortable it does have very substantial rebound damping so the bike is easy for beginners to stay in control on. Staying low and in control over bumps was however not enough and real dirt bike riders seem to have shunned the 1992 and later Italian Husqvarnas.
Another problem with the Italian Husqvarnas goes back to the 1991 models and may have been even more significant in the demise of the brand. The shortened 2.48 inch stroke of the 1991 Husqvarna 350 four stroke does not work with the oil reed valve lubrication system. Part of the problem may have been that the oil squirter was located too far away from the rod bearing on the 350, but the reality is that the oil reed valve lubrication system just does not work at sustained engine speeds above about 8,000RPM. The 1991 Husqvarna WXE 350 four stroke worked fine as long as it was either ridden slowly or ridden very carefully by someone familiar with the limitations of the oil reed valve lubricating system. For most dirt bike riders the oil reed valve lubricated 350 four stroke just self destructed for no apparent reason. The 1996 replacement of the 350 four stroke with the 410 four stroke made the problem worse. An even shorter 2.40 inch stroke length on the same big-valve cylinder head as the 610 four stroke meant much more power up to even higher engine speeds. Disaster for the oil reed valve lubricated rod bearing.
The 1991 WXE 350 may have been so prone to failure that it had no place being called a Husqvarna, but the 1996 Husqvarna 410 just immediately put the company out of business. In about 1997 new Husqvarnas disappeared and nobody seemed to know what happened. The word on the street was that the company went out of business, and this line went on for several years. Then when new Husqvarnas began to show up again around 2001 the mystery continued. It was a new U.S. distributor, the old distributor having gone out of business, and it also appeared to be a new company doing the manufacturing in Italy. The Cagiva brand name was still used on both sides of the Atlantic, but the Italian manufacturer suddenly was going by MV Augusta.
In any case the resurrected MV Augusta operation continued turning out revamped versions of pretty much the same 577cc four strokes along with more all new two stroke models including a Husqvarna 360 two stroke that was very well recieved. In 1998 a heavy 328 pound electric start 577cc SOHC Husqvarna TE610e street bike with the chain on the left side had been introduced, but it took a few years for this model to begin selling in significant quantities. The Husqvarna TE610e shares the same SOHC four valve cylinder head as the earlier Husqvarna four strokes, but the rest of the bike is very different and very heavy.
In about 2003 MV Augusta introduced the first truly Italian Husqvarna four stroke with the new dual overhead cam 250, 310, 400, 450 and 510 motors in an all new modern chassis. This was early enough in the 21st century four stroke conquest of motocross racing that Husqvarna was seen as a significant player and "in on the action". This despite the fact that the new DOHC Husqvarnas had only modest success at the highest levels of racing. Again it was the same problem as back in 1991, the bikes were expensive, unknown and just did not sell. The other problem was a complete lack of any sort of factory supported racing effort. The Husqvarna four strokes that were raced ran bone stock or minimally modified by some dealer or individual racer. No match for the Honda and Suzuki factory racing juggernauts with seemingly limitless automotive derived funding.
The new truly Italian Husqvarnas were an improvement in terms of being a somewhat smaller and lighter platform, but they were not really all that much smaller or lighter. The two camshafts added some bulk and weight, and worst of all that extra weight of a DOHC motor is all up very high and widely spaced at the top of the cylinder head. The Italian DOHC Husqvarnas were however finger follower valve trains. The finger follower DOHC engines are somewhat lighter and more compact than the Japanese cam and bucket DOHC valve trains and also have considerably more performance potential for an all out racing engine than the Japanese cam and bucket DOHC valve trains.
Another problem with the new truly Italian Husqvarnas was again related to the old Aermacchi long rod and short rod Sprint 250 motors of the 1960's. The new Italian DOHC four strokes shared platforms with different displacements. The result was a dual pairing of the same 97mm bore diameter for both the 450cc motor and the 501cc 510 motor and the same stroke length for both the 400cc motor and the 450cc motor. The big 2.67 inch (67.8mm) stroke length 510 motor got a smaller 38mm connecting rod big end bore and the smaller 400cc and 450cc motors got a larger 42mm connecting rod big end bore diameter.
That is decidedly backwards putting a bigger rod bearing on the smaller, shorter stroke length motors. Obviously the 38mm big end bore on the 510 motor is already somewhat oversized, that's the same big end bore diameter used with great success on the three inch stroke length 610 motor. Using an even larger 42mm big end bore on the 2.39 inch (60.76mm) stroke length 400 and 450cc motors is just out of this world ridiculous.
So the new DOHC Italian Husqvarnas had a somewhat smaller engine platform than the old Husqvarna four strokes, but that smaller engine was really a 501cc thumper with a 97mm bore. Not exactly a small dirt bike motor. At least the new DOHC Italian Husqvarnas came with dual rotary lube oil pumps to keep those oversized rod bearings well lubricated up to high engine speeds.
The new truly Italian Husqvarnas languished on for several years but the, by then, routine fate of Italian Husqvarnas closed in and the company once again went out of business. In 2007 BMW bought the Husqvarna name and the tooling for the then current Husqvarna models and in 2008 Harley-Davidson purchased MV Augusta/Cagiva and ended up with their old Aermacchi production facility back.
The ultimate result of Harley-Davidson getting back into Italian motorcycles seems to be in some way related to the new water cooled four valve per cylinder Harley-Davidson Street 500 and Harley-Davidson Street 750 models introduced in 2014. The new "Street" models represent a number of firsts for Harley-Davidson; including overhead camshafts and four valves per cylinder. Some Harley-Davidson models have had water cooling before, but it has been marketed as an add-on hybrid system. The Street 500 and Street 750 are the first Harley-Davidson models to be marketed as water cooled engines. The Street 500 and Street 750 are also the shortest stroke length Harley-Davidson models that have been available in quite some time with both models sharing the same 2.60 inch stroke length. Perhaps not quite as bad as the short rod and long rod Sprint 250 bikes of a half century ago, but it does look like the Street 500 and Street 750 share the same connecting rod and the same cylinder heads. The 750 is just a big bore kit on the 500.
Production of Husqvarna bikes continued in Italy under BMW, and in 2012 a new more compact DOHC 250cc four stroke Husqvarna motor was introduced. This new 2012 Husqvarna TC 250 four stroke used a very short 2.00 inch (50.9mm) stroke length, the shortest stroke length production 250F dirt bike to date. In 2013 BMW dropped it's foreign manufacturing and parts sourcing to go back to being an entirely German auto and bike maker. Stefan Pierer, CEO of KTM, purchased Husqvarna AG on January 31st 2013 and renamed the brand Husqvarna Sportmotorcycle GMBH. The tooling and remaining parts stocks for the Italian DOHC Husqvarnas as well as the former Husqvarna facility in Biandronno was purchased by the resurrected Italian motorcycle company SWM with former Cagiva and Aprillia Engineer Ampelio Macchi. The first new SWM bike is a big heavy 144kg DOHC 650 sincle cylinder dual sport dirt bike that displaces only 600cc. Sound familiar? The stroke length of the SWM 650 is 76.4mm, which was how the 3.01 inch stroke length of the Husqvarna 610 was listed by MV Augusta in later years. In the early 1990's the 3.01 inch stroke length was listed by Cagiva as 76.5mm. Steel tube frame with a single upper tube, Brembo two piston front caliper, Marzocchi upside down forks. The SWM RS650R all sounds very Husqvarna like, except of course the DOHC motor and the huge weight.
Is it KTM dirt bikes with white plastic or Husqvarna dirt bikes with orange plastic? The interesting tidbit of information is that KTM never owned the Husqvarna name. Some Austrian guy named Stephan Pierer owned 51% of KTM and managed to accumulate enough personal wealth to purchase the Husqvarna name from BMW. Having a controlling interest in both KTM and WP Mr. Perrier was in a position to start selling KTM dirt bikes with white plastic and the Husqvarna logo. The next thing that happened though was that an all new model was introduced very early in 2015 for the 2016 model year. This new KTM 450 SX-F/Husqvarna FC450 most certainly is the new Husqvarna. It is finally as fast as a 1991 Husqvarna WMX 610, something that the 2012 through 2015 KTM 450 SX-F was already steadily pushing towards. The new model really is a KTM in that it is the next step in a quarter century long development process, but it only happened after the Husqvarna name was in place.
A Husqvarna in name only perhaps, but so was the 1983 air cooled four stroke, the 1987 water cooled four stroke and the 1991 610 four stroke. The difference is that in 1983, 1987 and 1991 it was just a few key upgrades to the old platform. But where did that KTM four stroke platform come from in the first place? An early 1990's KTM 600 four stroke looks an awful lot like a Husqvarna four stroke or a Husaburg four stroke. Obviously KTM was just copying the Swedish four strokes. The parts might not be directly interchangeable and the bikes may have very different manners and characteristics, but the similarity is more than just that they are all four strokes. They are the same four strokes, with the same layout. Part of this is that it is just a very good design that is hard to improve on. When KTM decided to make a four stroke they started with the Husqvarna four stroke and tried to improve on it. They most certainly did improve on the original 1987 water cooled Husqvarna four stroke, but a big part of why the KTM four strokes of the 1990's worked so well was that KTM did not deviate much from that design for the sake of making it look different.
The biggest failings of the late 1990's and early 21st century KTM four strokes was also in copying some failed design features of the Husqvarnas. The big 313g connecting rod of the 610 four stroke being used in the short stroke 350 and 410 Italian Husqvarna four strokes is repeated in the KTM 250/400/450/520/525/530 motor and the KTM 400/600/620/625/640/660/690 motor. KTM did build two motors. One was a 520 and one was a 625/640/690 and both were offered with dramatically smaller displacements. Very confusingly both motors were offered with a 400cc displacement, first the 400cc LC4 in 1994 through 1999 and then from 2000 to 2011 the 520 was available with a 400cc displacement. Both of the 400 motors shared the same 89mm bore and 64mm stroke length, but one was on the big LC4 platform while the other was on the smaller and lighter 250/520 platform. What KTM did do though was continue on with the use of the pressure lubricating systems. The original KTM 250 four stroke might be a cumbersome, heavy poor performer shackled by the 520 connecting rod and transmission, but at least it has two oil pumps that push massive amounts of oil everywhere it is needed at any attainable high engine speeds. And that rod is really ridiculously big and heavy even for the 520. It is 129mm long center to center and has a 43mm big end bore. Compare that to the 127mm center to center length and 38mm big end bore of the Husqvarna 610 rod. The KTM 400/620/640 LC4 uses an even bigger 141.5mm center to center connecting rod with a gargantuan 50mm big end bore.
The introduction of load dependant spark timing on the 1998 KTM four strokes can also be seen as a continuation of Husqvarna development. This is not clearly either a success or failure, and how it actually relates to Husqvarnas is a bit murky and contentious. It is not that the 1990's or earlier Husqvarnas actually had any sort of a sophisticated ignition system, it is just that some of the Husqvarna ignition systems failed to work in such interesting ways that they seem to be related to later ignition system developments.
The 1990 through about 1993 SEM ignition systems on the Husqvarnas are so prone to failure and so difficult and expensive to replace that they seem designed to get points on the bikes. And then there is that miniscule little half a degree of crankshaft rotation advancing effect around 5,000RPM on the SEM CDI ignition systems. It all just seems to add up to some engineer at SEM or Husqvarna lamenting the passing of points ignition systems that could provide some substantial crankshaft wiggle advance. The mundane fixed advance curve of a CDI ignition system was somehow lacking.
The whole KTM/Husqvarna entanglement really goes back to the formation of Husaberg Motor AB in 1988 after the sale of the Husqvarna Motorcycle division to Cagiva. Husaberg was founded by former Husqvarna engineers led by Thomas Gustavsson and the immediate focus was competitive four stroke race bikes. Unssuprisingly the new Husaberg four stroke was extremely similar to the 1987 water cooled Husqvarna 510. The Husaberg shared nearly identical bore and stroke dimensions with the Husqvarna 510 and the layout of the engine was exactly the same as on the Husqvarna four stroke. The engine parts were so similar in fact that it almost looks like some of them would be interchangeable.
In an interesting twist the Husaberg factory racing effort was led by Italians. Brothers Alvaro and Guido Vertamati had been the Italian Husqvarna distributors in the mid 1980's, but they switched to Husaberg in 1989 after a falling out with Cagiva. In both 1990 and 1991 Husaberg won World Enduro titles. In 1991 Italian Walter Bartolini got noticed durring the F.I.M motocross series by pulling some massive hole shots. Bartolini might not have been able to hold off the top factory riders to convert the hole shots into significant numbers of podium finishes, but he did make a statement that 500cc four strokes were not necesarily all that weak and slow compared to 500cc two strokes.
For 1994 the bore size of the Husaberg 501 was increased from 92mm to 95mm, no doubt to better compete with the de-stroked Husqvarna 610. In 1993 Joel Smets made a very good showing on a Husaberg coming in third in the F.I.M. 500cc motocross world championship behind the Swede Joergen Nilsson riding a two stroke Honda and fellow Belgian Jacky Martens on the factory Husqvarna 610. Four strokes certainly were on the rise by the early 1990's.
In another bazaar turn of events the Vertemati brothers then had a falling out with Husaberg and went on to field their own race team for 1994 with an entirely custom hand built race bike. The Vertemati race bike was of course very similar to a Husaberg, and in fact it used the entire cylinder head off of a Husaberg 501. The rest of the bike, including the gear box, was however custom built and the Vertemati used White Power suspension. In 1994 Joel Smets again came in third in the F.I.M motocross world championship on the Vertemati four stroke behind Jacky Martens on the factory Husqvarna 610. This time it was another Swede riding a Honda two stroke, Marcus Hansson, who won the championship in 1994 beating out the dueling Swedish/Italian thumpers. Joel Smets finally got his F.I.M. 500cc world motocross championship victory on a Husaberg four stroke in 1995. Smets went on to win again in both 1997 and 1998 beating out Darryl King on a factory Husqvarna 610 both years. With the introduction of the Yamaha 410/400 four stroke in 1997/1998 and new KTM four stroke models in 1998 the two strokes were mostly gone from F.I.M. motocross racing.
The last F.I.M. 500cc motocross world championship to be won on a carbureted two stroke was 1996. The rider was Shayne King riding the KTM factory racing 360 SX two stroke. A two stroke engine displacement long associated with Husqvarna by the way. Shayne King, younger brother of Daryl King, was New Zealand's first motocross world champion. Lots of brothers in this story! In 1999 Yamaha became the first Japanese manufacturer to capture a motocross world championship on a four stroke. Riding the Yamaha factory racing YZ400F in 1999 was the Italian racer Andreas Bartolini, younger brother of Walter Bartolini who had first campaigned a Husaberg four stroke eight years earlier. It was of course also a Yamaha YZ400F four stroke that Dough Henry won the 1998 AMA National Championship with racing against only 250cc two strokes. At that time AMA rules allowed up to 538cc of four stroke displacement in the 250cc two stroke class. Yamaha decided to race with only 400cc of displacement on a 2.37 inch stroke length, and that turned out to be plenty to best the long 2.83 inch stroke length 250cc two stroke motocrossers.
In 1996 KTM bought the financially struggling Husaberg but production remained in Sweden until about 2000 when the entire operation was moved to Austria. When Joel Smets won the F.I.M. 500cc world motocross championship a fourth time in 2000 it was on the new KTM 520 four stroke. How much does a stock 95mm bore and 72mm stroke length 1998 through 2011 KTM 520/525/530 displace? Yup, 510cc. How much does a 2012 through 2016 KTM 500 and 2014 through 2016 Husqvarna 501 displace? Yup, 510cc from the same 95mm bore and 72mm stroke length. It's the same basic SOHC KTM RFS engine even if it was worked over a few times since it was originally introduced as a 250cc four stroke way back in about 1995. The significant change being a new cylinder head with giant 40mm intake valves and 32mm exhaust valves for the 450cc displacement sometime roughtly around 2007. All of the earlier KTM 250/400/450/520/525 models used the same cylinder head casting with the same valve spacing as the original 250 model. That was 35mm intake valves and 30mm exhaust valves for the 400/450/520 models and 28mm intake valves and 24mm exhaust valves for the 250 model. For 2007 the KTM 450 also got a much shorter connecting rod, but it was still on a 35mm crankpin with a giant 42mm big end bore. For 2013 the KTM 450 got another new connecting rod, this time with a plain rod bearing instead of the traditional roller rod bearing. This new 2013 KTM 450/KTM 500 rod uses a substantially smaller 39mm big end bore on the same 35mm crankpin, and is longer at 114mm center to center. Then for 2016 the all new SOHC KTM 450/Husqvarna FC450 once again got a shorter 108mm center to center length connecting rod to go with the overall slightly lighter and more compact motor layout.
How about a 91.5mm bore by 76.5mm stroke length 1983 through 1989 Husqvarna 510? How much does that displace? That's 503cc, and it originally used rather small 33mm intake valves and 30mm exhaust valves when it was introduced as an air cooled model. The spacing between the valves was however for a much larger bore diameter than the original 91.5mm bore size. The same cylinder head casting gulps down the bigger 36mm intakes and 32mm exhausts of the late Italian Husqvarna 610 while retaining the ability to go on the original 91.5mm bore. The spacing between the valves and the basic shape of the casting is however for the bore size set by the cylinder stud spacing and the ability to very easily and effectively go up to even larger valve sizes is designed right into the original castings. The absolute maximum would be 40mm intake valves and 36mm exhaust valves. There is even room for bigger valve springs, both on length and on diameter. Yup, that's a big thumper. So how is it that KTM has stuffed 40mm intake valves into a 95mm bore diameter? It's because that was what they were trying to do with the cylinder head design. The goal was not absolute maximum performance, no the goal was absolute maximum intake valve diameter.
Particularly with an aggressive overhead roller camshaft maximum performance is obtained with a bit of space around the valves so that the cylinder walls don't overly shroud the open valves. So what is the bore diameter that the original Husqvarna 510 four stroke was designed to work best with? Is it as big as the 95mm bore of the KTM and Husaberg thumpers? Yes, absolutely the 1.575" intake valve spacing on the Husqvarna is for a bore diameter bigger than 95mm. How about the 98mm bore of the 610 motor? Again, yes. It flows better at the 98mm bore diameter. The 102mm Cagiva W16 bore diameter? No, not that big. The valves don't need to be that far from the cylinder walls. What would the absolute largest bore diameter be for an air cooled cylinder on the 126mm bolt circle for the 10mm cylinder studs? Way out at about 108mm, which on the 76.5mm stroke length would be 701cc.
The conclusion? The Swedish SOHC Husqvarna was originally designed to be a water cooled engine with about a 96mm to 98mm bore diameter. The last piece of the puzzle is that the valve layout on the Husqvarna 510/610 motor favors a rather large exhaust valve size. With this long of stroke length the engine speeds remain low enough that getting it to flow well is not all that difficult. A more aggressive camshaft and bigger valves always result in somewhat better performance over a wider range of engine speeds, but the bias on the Husqvarna 510/610 motor is towards efficiency. Bigger exhaust valves are moslty good for improving efficiency under a full load. Sort of ridiculous to favor full load efficiency over peak power output for a dirt bike motor, but the design is biased towards efficiency none the less.
In 2003 the F.I.M. premier class displacement limit was reduced to 450cc and Honda, Yamaha, Kawasaki and Suzuki introduced 450cc four stroke race machines. Or rather Honda introduced the CRF450R for 2002 and F.I.M. followed big red. The 2002 Honda CRF450R is actually a very interesting model in that it's frame geometry with 28.6 degrees of rake and a wheelbase of 59.4 inches is very Husqvarna sized. For 2003 the Honda CRF450R, and most subsequent 450 four strokes, have a steeper 27 degree steering head angle and a shorter 58 inch wheelbase length. Small, but significant and noticeable changes.
Even after the entire Husaberg manufacturing and development operation was moved to Austria in 2000 a Husaberg Motorsport department remained in Sweden. With Stephan Pierer's accuasition of the Husqvarna name in 2013 the Husaberg name was discontinued after the 2014 model year.
Husqvarna got their start in motor sales with the Swiss Moto-Reve, and now the Husqvarna name is owned by some Austrian with an extremely French sounding name. The next step would seem to be for Husqvarna to source a Swiss motor for Husqvarna motorcycles. Swiss motor? Wait, they don't make motors in Switzerland, do they? Perhaps a German Hatz diesel converted for use in motorcycles by both Renault and BMW.