Armen
Serious Thumper
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Half-Witted Wrench-Jockey from Jersey
Posts: 1452
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Both Dave and DBM experimented with lighter flywheels. I made a few different weight ones, one light, one real light. Dave found that the bikes accelerate faster with the light flywheel, DBM found that there was a loss of top end with the ultralight flywheel. Kevin Cameron (my fav bike tech writer) of Cycle World, posted this piece this week. He was talking about crank and cam flex in high speed motors. In there somewhere, he got to the subject of making cranks and flywheels too light. Here is part of what he wrote:
"Now that we know this rpm of valve float with this combo of cam-lobe shape, valve spring, and valve and tappet weight, we can compare it with what happens in a real engine, which does not have a heavy flywheel on its camshaft to smooth out its rotation.
When Honda’s HRC made such a comparison, it found that valves in a running Formula 1 engine it was developing began to float at roughly 1,500 rpm earlier than in the above-described test with a heavy flywheel closely coupled to a single cam lobe. Why? The rapid variation of cam-lobe-instantaneous rpm, caused by torsional vibrations in the crankshaft and camshaft, was causing cam lobe rpm to “flutter.”
I felt a glimmer of understanding. Both thingy O’Brien, Harley-Davidson’s long-serving racing manager, and Rob Muzzy, the successful Superbike engineer and team manager, had independently told me the same thing: “Every time I’ve tried to run a lightened crankshaft at Daytona I’ve lost top speed.” The lighter the crankshaft, the larger its speed variation at each cylinder firing. And that speed variation is transmitted through the cam drive, leading to degraded accuracy of valve movement—and loss of power."
So, maybe we are seeing valve float at high revs with a light flywheel?
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