Hawk Talk

Ariel Red Hunter · 08-23-2016, 02:07 PM

An overhead cam engine. Hmm. there are trade-offs, as always. Engine is almost always taller. (Except certain weird designs, like the face-cam Chater-Lea). Very difficult to make as light as a push-rod job. If it is a chain drive, should have a 50% reduction to the chain. That way the chain runs at half of engine speed. For a racing engine, with the best parts obtainable, built virtually without regard to cost, taking the reduction in the chain drive system is acceptable because of less weight. We now live in the age of total mass-production. So an engine is now designed for a purpose, not just as a lightweight, junior, or senior class. Road bikes are the most popular class. So an engine is usually designed for a roadster, where acceleration and top speed is very important, especially in the lightweight class (250cc). Then, if the powers that be decide an enduro/dual sport is required to fill out the line, it should be no surprise that they look at the engine they are already building, for reasons of cost control. Perhaps they design a more tractable cam and fit a smaller carburetor. But the porting stays the same, which is really too big for an off-road bike engine. Of course, when cost is no object, then we have bikes like the KTM.

08-23-2016, 02:07 PM	#10
Ariel Red Hunter Join Date: Jun 2016 Location: akwesasne, NY-13655 Posts: 2,220	Hawk talk lll An overhead cam engine. Hmm. there are trade-offs, as always. Engine is almost always taller. (Except certain weird designs, like the face-cam Chater-Lea). Very difficult to make as light as a push-rod job. If it is a chain drive, should have a 50% reduction to the chain. That way the chain runs at half of engine speed. For a racing engine, with the best parts obtainable, built virtually without regard to cost, taking the reduction in the chain drive system is acceptable because of less weight. We now live in the age of total mass-production. So an engine is now designed for a purpose, not just as a lightweight, junior, or senior class. Road bikes are the most popular class. So an engine is usually designed for a roadster, where acceleration and top speed is very important, especially in the lightweight class (250cc). Then, if the powers that be decide an enduro/dual sport is required to fill out the line, it should be no surprise that they look at the engine they are already building, for reasons of cost control. Perhaps they design a more tractable cam and fit a smaller carburetor. But the porting stays the same, which is really too big for an off-road bike engine. Of course, when cost is no object, then we have bikes like the KTM.
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