The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: BSA500 on 21.11. 2012 22:41

Title: Balance factor
Post by: BSA500 on 21.11. 2012 22:41

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???

Title: Re: Balance factor
Post by: metalflake11 on 22.11. 2012 00:18

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

Title: Re: Balance factor
Post by: muskrat on 22.11. 2012 11:37

 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) *eek*
Cheers

Title: Re: Balance factor
Post by: trevinoz on 22.11. 2012 19:42

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

Title: Re: Balance factor
Post by: muskrat on 22.11. 2012 19:58

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

Title: Re: Balance factor
Post by: BSA500 on 22.11. 2012 22:15

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

Title: Re: Balance factor
Post by: Housewiz on 03.12. 2012 01:42

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

Thanks,

Steve

Title: Re: Balance factor
Post by: KiwiGF on 03.12. 2012 08:56

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

Title: Re: Balance factor
Post by: duTch on 04.12. 2012 11:23

 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