balancing 500 single crank

[john a sheppard]

quote:
John, I saw now that I made a typo in the GPM piston weight, should be 592 g, not 692 g.
I checked balance with GPM and found no change required. Of course balance could have been adjusted already by a previous owner.
In my opinion you made a calculation mistake. Did you correct that, or am I wrong?
Albert

[john a sheppard]

Yep. In my enthusiasm and not reading the comments properly I did make a calculation error and as pointed out forgot to subtract the con-rod weight. realised too late as I had already drilled out (I have also machined out some of the piston). Now my query is do I correct by counter drilling the heavy end. I need to reduce about 56g at the outer diameter. This means I will have reduced the mass off the flywheels by about 146g At the outer diameter in the side). I do not have the weight of the flywheels but it seems to be more than 5kg. Thus 146g is not that significant (about 2.6%). Does anyone have a feel for how much you can reduce the mass before it affects the running?

[zwarts]

I would say that provided you keep the balance factor the same, then a 2.6% reduction in flywheel mass would not be detectable when you are riding the bike. I notice from the above that you are working to a 60% balance factor whereas, in Fred Neill's handbook, covering the single cylinder models from 1946 to 1960, the B.F. is given as 65%.
I usually work to the 65% figure, but the 500cc singles still get 'the shakes' at higher rpm!
Bob.

[john a sheppard]

Thanks Bob. It is very encouraging. I have also taken the advice to use a 65% balance factor. I am just working up the courage to drill again. Best Regards
John.

[aobp11]

quote: I need to reduce about 56g at the outer diameter. This means I will have reduced the mass off the flywheels by about 146g
I must confess that I don't understand what you mean here. 146 g seems an incredible lot. If you want to be absolutely sure that you make no errors, then supply again the details:
- complete piston weight (was 610 g but less now),
- small end weight (still 174 g),
- reassemble crankshaft including con rod and big end nuts; by trial and error determine the weight to hang at the small end to give balance. What was that weight?
or
reassemble crankshaft leaving away conrod and rollers and cage; determine weight to hang at the bigend and so on. Now additionally the total weight of "left away" things is required.
- the desired balance factor.
Albert

[aobp11]

quote: Does anyone have a feel for how much you can reduce the mass before it affects the running?
Look at it from the bright side. The more you reduce, the faster you can accelerate. Removing mass at the outer diameter is most effective for this! Stop when slow idling gets impossible.
Albert