crankshaft balance

What's generally the right way for getting the crank balanced right? Is there a figure or dimensions for 175 crank , the tuning manual has drawings for a 125 crankshaft only ,

dansofield550 wrote:

What's generally the right way for getting the crank balanced right? Is there a figure or dimensions for 175 crank , the tuning manual has drawings for a 125 crankshaft  only ,

Hi Dan and All,

Good to be here!..............

This is our method working on each web separately:
For static balancing Nick's 186 we weigh the piston complete with rings, pin,circlips plus small end bearing,set the rod horizontal with the crankpin supported on v blocks and measure the weight of the small end eye.
Next the small end is supported and the big end,crankpin and cage is weighed.
The weight of big end plus 55% of the small end/piston sum is then halved and translated into a dummy metal crankpin of the calculated weight!

With the web between centres,and the dummy crankpin in position, metal is removed from the outer rim side face until the web remains still in any position it is placed!
If it moves, showing unbalance, metal is removed at the low point(bottom)!
The time spent doing this accurately seems to be well rewarded!
We always machine the web diameters and widths to an equal size!
Nick reports any vibration is minimal compared to other 175's he has ridden!

There may be other/better ways but this seems to give reasonable results!
We welcome other ideas and results?

Keep up the Good work!.............Rex and Debb

PS. This is only a guide as frame design/weight can all enhance/absorb vibration!

thanks Rex,
thats kind of how i was going about it , only i had the figure of 65% in my mind for some reason , not sure where i got it from as i can't find the source of why i used that number!,

i seem to recall a sliding scale of rpm and percentages but again not to sure if i'm recalling it right!

Hi Dan,

We have also tried 65% and not found a lot of difference!

Maximum rpm might alter it as well!
Nick's motor peaks at 7750 revving on to 8500 so it is quite a low revver!

Cheers!..........Rex and Debb

thanks again Rex , i'll be doing the balancing today, made a dummy bigend already and weighted it to the right grams, just been searching for the balancing jig, it might be tucked away safe !