FYI
Here:
http://www.ajs-matchless.com/article_read.asp?id=26Balancing.Balancing seems to be a field the average motorcycle owner is reluctant to dig into. It might, on the first hand seem to be a sophisticated task, but it's not. There are given criteria to carry out the job from. Combined with some judging. The latter which makes this a very interesting modification to do.
And for those who are preparing race engines, sharpen your eyes. It's better to shiver from horror instead of being shaken to death by the engine. It will keep the bottom ends together.
To start with an end, the balancing factor is the difficult bit, and the one which must be judged. It can vary from 50% to 90"%. Roadsters are usually in the 60% to 70"% region, and racers 70% to 85%.
As you can see from the list below, factors are varying. These are parallel twins, hence they can be seen in relation with single cylinder engines.
Royal Enfield 65%
Triumph twins 78%
B.S.A. 70%
Commando (rubber isolastic) 52%
Commando (tight shimmed or bolted) 70-75%
Commando (bolted to frame) 82%
Weslake 80%
The effect of the values simply explained are:-
The lower the percentage, the more vibration at high revs. (Heavier pistons give this effect).
High values give more vibration at low revs.
Con-rod geometry, combustion/compression pressures influence the factor in such a way that it is advisable to compare one engine type with another, and you must be aware that it is impossible to make our engines vibration free through the whole rev-range. There must be a compromise. So, how are you using your engine? 2000 - 4000 rpm cruising or is it a 5000 - 7000 rpm sort of job?
How do we find the necessary values? First you have to judge your old crank in two ways, one reciprocating part, and one rotating part.
Lyder Moen, Braathens lnd. Div., 4050 Sola, Norway
Issue 382