We dug deep into our archives and located particulars on a twin-cylinder 490cc Husky prototype from 1967. This machine would show to be the premise for a profitable machine launched a 12 months later, in 1968. The Siamese motocross twin racer from Husqvarna was a primary of its sort. It was developed for the U.S. market considering of desert races and long-stretching enduros such because the Baja 1000, the place it was very profitable.
At first of the 1960s the Husqvarna manufacturing facility chief engineer Ruben Helmin had an concept of placing two 2-stroke engines collectively. It could end in a potent twin energy plant with a displacement of half a litre. It wasn’t till within the autumn of 1967 that he started creating his ideas into actuality.
Helmin used two 250cc engines and built-in them into one energy unit. The pistons have been the identical because the common 250 with two rings on every piston versus the later 504 model with just one ring for every piston. The outcome was a 492cc motor mounted right into a 360 body. The modifying consisted of different engine plates and used the gearbox and elements from the 420cc Grand Prix bike, then used on this planet championship.
“The engine developed some 50 horsepower at 6,000 rpm,” mentioned Ruben Helmin when the bike was launched in 1968. The brand new Siamese twin racer was meant for the desert, however initially there have been additionally hopes for a brand-new machine to compete with the massive bore bikes extensively used for motocross at this stage.
Motocross riders Torsten Hallman and Rolf Tibblin, representing the 250 and the 500cc class respectively, made take a look at runs with the brand new beast, which had a lot of energy and a 100+ mph high pace.
“It was undoubtedly not a machine for motocross,” have been the unanimous feedback from the 2 world champions – however they’d be confirmed improper.
After an extra 12 months of growth, the enormous Husqvarna beast was over-bored to a displacement of 504cc, which made it eligible for the worldwide FIM cup throughout 1969. This machine now had two higher exhaust pipes versus the prototype, which had one in all its exhausts swept beneath the 360 body. This didn’t give the bike enough floor clearance and the exhaust was quickly modified to a two-into-one system. The 2 pipes have been introduced collectively slightly below the gas tank, which additionally needed to be adjusted for desert use. It may swallow as much as 15 litres of gas and was fixed with leather-based straps for a fast launch. The total tank weight of the race-ready machine was 137 kilos.
Baja winner Gunnar Nilsson was given the job to trip the bike by the Husqvarna manufacturing facility. Within the five-race sequence, Gunnar went to beat the big-bores and received the FIM championship. Reliability and efficiency proved to be wonderful. This win proved extraordinarily standard and the advertising and marketing folks now began to think about manufacturing of the dual racer. Regardless of the worldwide success, the venture was nonetheless solely at an experimental stage.
Bench figures from 1968 confirmed that the ability output was now 52hp at a wholesome 6,800rpm. The highest pace was clocked at 110mph utilizing a rear sprocket of 47 as an alternative of the generally used 53 ratio. For carburation, the Amal 32mm concentric carb was dealing with the respiratory. Two throttle cables have been used from the carbs all the best way as much as the throttle grip. A Bosch ignition system was fitted and had a barely altered efficiency versus the usual model. The flywheel and the magneto initially got here from a snowmobile, nevertheless nonetheless the identical measurement as for the 400, however stronger for the dual.
With this growth, the body needed to be strengthened to deal with the extra energy assets. Mainly, it was now the identical as for the 400 Husqvarna. Heavy engine plates have been used to match the massive energy plant. Two additional brackets have been mounted beneath the engine to function skid-plates. Additionally they supported the body and the footpegs.
After success within the FIM sequence, a 492cc machine was shipped to the USA for participation within the Mexican Baja 1000 race. With the 2 ace riders Gunnar Nilsson and J.N. Roberts they managed to win this traditional occasion by margin, regardless of a late crash at nighttime. Gunnar Nilsson needed to spend virtually half an hour trying to find his bike in whole darkness. Fortunately, the incident occurred near the end in La Paz.
The general win was adopted by just a few different US races, however with out a lot success. It was then determined to not proceed the venture and the bike was forgotten in storage till it was rediscovered within the 1990s.