Prior to the 1980s, Husqvarna had designed only two-stroke motorcycles for decades. So, when they designed a new 510cc four-stroke motor, they based it on their existing two-stroke bottom end and employed quixotic but logical engineering to lubricate the engine. Rather than a positive-displacement oil pump and dedicated oil lines, the engine utilized nothing but changes in internal engine air pressures and a pair of tiny, simple reed valves to coax the oil where it needed to go.
As the piston rose, it created a vacuum the crankcase, which sucked oil through a carefully designed set of orifices to lubricate major engine components. When the piston came down, one reed valve would shut and another would open. The resulting pressure would push oil up through the cam case to lubricate the cam chain, overhead cam, and valves. The other components in the engine and transmission were splash-lubricated by the spinning of the internal components, just as they were in a two-stroke engine. The engine housed a scant pint of motor oil.
The result was a remarkably light, compact, and simple engine that didn’t look all that different from their two-stroke models. Surprisingly, the super basic oiling system was quite robust, and the engines were fairly bulletproof. The odd lubrication technology’s only drawback was inadequate oiling at steady throttle settings, making the system inappropriate for a freeway flyer.
Two-Wheel Tuesday: Radical Simplicity
3 responses to “Two-Wheel Tuesday: Radical Simplicity”
That’s partly why Yamaha gave their XT/TT/SR 500 singles a dry sump, with the oil stored in the frame. That and making the motor lower, which wasn’t apparent in the final product.
Honda didn’t bother with that with their XL/XR/GB 500 singles which were lighter and more powerful than the Yamaha. So cavalier/confident were Honda about the robustness of their design, they didn’t even have an oil filter for their wet sump oil supply. I used to change mine less often than I should but never had any trouble. I had been about to buy a Yamaha XT 500, but Honda’s new XR/XL 500s came out new for the same price as a second hand Yamaha, I bought the fourth XR in the country, a very early, almost preproduction ‘Z ‘model that preceded the ‘A’ model, and sold it after 7 years use for more than I’d paid for it. I read about the Husky in the bike mags but no-one was importing them, I’ve still never seen one in real life. That innovotive design saved weight, reduced friction and gave more power.
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