Balance factor

[BSA500]

If I am to have the crank balanced the firm need to know a % but as i have seen on many posts here that is a very very large can of worms. Is there a 'standard' figure to use for a pre unit A7 crank ie from BSA themselves???

[metalflake11]

I've seen a few % figures bandied about, and different methods too!............ I can only give you my personal experience, which I hope is of use.
I had my crank done at S.R.M. and they did it using the 'Dynamic' method. This involves weighing the pistons, gudgeon pins/clips and conrods and then off setting that weight by doing something in sympathy to the crank. Not a very technical explanation I know, but the net result was an engine that vibrates evenly from low to high speed. I did 90 mph once and it was still fine, but sympathy for 50 year old conrods soon had me back down to the usual 60 mph! At all speeds you can see through the rear view mirror, and no more having to find a speed the bike is happy with, it's always happy. That's the road I would go down if I ever have to do it again, what do others think?
                  Rob

[muskrat]

 65% seems to be the magic figure for road use. I went up to 72% on the A7SS racer, smooth as silk at REDLINE (8000rpm)
Cheers

[trevinoz]

Standard is 54% and 65% is supposedly the figure for racing.
Trev.

[muskrat]

 Thanks for correcting me Trev. Long hard day and those figures just jumped out.
Is the 54% std for both A7 and A10?
Cheers

[BSA500]

so I would go for the 54% for every day(and I mean every day) riding.

[Housewiz]

OK, this rookie needs someone to elaborate - what's the 54 & 65 percent you guys are tossing around?

Thanks,

Steve

[KiwiGF]

This link has the answers but calculating the balance factor is not that simple ......

http://www.a7a10.net/forum/index.php/topic,6086.0.html

[duTch]

 I want to throw in my two bobs worth, but will have to wait till I've done a lap or two, see if I got it wrong or right maybe soon