Suck Squeeze Bang Blow

crazypj said:

The weight of inner spring isn't the problem the resonant frequency could be.
Beehive springs have a naturally higher frequency, plus, the generally smaller retainer is lighter, if your using the same size or larger it's a disadvantage (rocker arm will probably contact retainer edge)
On a CB175/200 you would have to rev it to about 38,000 rpm before valve spring resonance is a problem ;D
The parasitic power loss is usually lower with beehive springs, but, it's easier to put a 30 degree back cut on valves to make them lighter and use stock springs (the back cut also helps low lift flow)

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mydlyfkryzis said:

Dial indicators and accurate STATIC measurements of timing are nice. But you take a cam and crank at 10000 rpm and the actual timing will vary from the torsional flexing of the crank and cam.

No matter how good static timing is, the actual position of the crank and cam can rarely be known.

With the crank itself accelerating and decelerating, cam chain stretching and springing back, the reality is the engine is just a bunch of springs bouncing around. When you look closely at rotational vibration in an engine, you often wonder how it runs at all. And bikes have relatively short cams, usually driven from the center. Take an inline six auto engine and the long crank and cam really get to shaking around.

Even non-reciprocating equipment has lots of torsional vibration. I work on electric and steam driven turbo- machinery. Some of the vibration spectra are downright frightening. You can't believe how much a 6 inch diameter steel shaft can flex.


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