ned37 said:
i removed the counterbalancer from my 02 650 about 1000 miles ago and did not rebalance the crank. i can't remember the numbers for the various weights of the rotating components, but seem to think stock it is about a 40% balance factor. my logic at the time was that since i'm riding it on very bumpy roads and trails that the vibration wouldn't be that noticeable. wrong. its very noticeable. the various sources on this board that have balanced cranks use anywhere from 30 to 70%. ??? anybody have an idea what a good balance factor would be for running most of the time at about half to 3/4 revs? any idea of the cost?
Hey ned37,
The thing with balance factors is that they really do tend to vary in "rightness" according to personal preference rather than an exact rule.
The actual balance factor of each engine has several variables but you're correct in that the 02 650 is around the 40% mark with c/b removed.
Now, Lineaweaver used to aim for approx 75% and that's where that figure has come from, the 40% approx with just c/b removed was from my experiments with a variety of weights over a period of time with my old 2001 650.
The discussion here is really to do with static balance but when it gets to how it behaves dynamically the picture begins to change. That's because when balancing a single what we're really talking about is changing the direction of the resultant forces of piston/conrod/crankshaft rotation because a single cannot be properly "balanced" - there's no way we can balance reciprocating mass with rotational mass.
In addition, despite a certain balance factor, once the engine is running, how that actually reduces vibration depends also on the forces of the various masses. This varies, of course and one important variable, for example, is conrod length as this affects piston acceleration, thus force. So, for a given reciprocating mass your conrod length may reduce or increase the overall forces regardless of the balance factor - remember, the balance factor being referred to here is just the mass of reciprocating parts, not their force caused by acceleration.
These are some of the reasons I personally avoid getting into any discussion on what the right b/f is for an individual. In your situation, however, it seems as if getting the crank dynamically balanced might be an option to consider? Other than that, why not fire Lineaweaver a note?
As for counter weights, the traditional way to re-balance the crank is by drilling holes and re-filling those holes with mallory, which is twice the mass of the steel - doing that you avoid any risks of the weight coming loose and any spacing issues to the side of the crank web.
Cheers,
Simon
