An example of how far balance can be out and still be ok to use. I built a Brough SS100 replica and fitted it with a crank and rods from 1323cc SV engine, it was beautiful and smooth up past 90mph (as far as it'd been at that time) BUT at tickover the forks the forks flapped back and forward violently so I though I would have it balanced and sent the crank off to a specialist. they came back to me and said it was so far out the motor should have self destructed and my eyeballs pop out, instead of their normal 42% balance mine was 86% !!!!!
All around the rim on the crank pin side were 25, 3/8" blind holes and they said the only way to balance it was to take that much away opposite that they didn't want to do it so I got the crank back.
My solution, clean and tin the holes, pour molten lead into them and tamp it firmly down, then check the balance, I ended up drilling the lead back out of one hole.
Result, lovely and smooth at the bottom end and up to 100mph with a slight tremor around 55 mph.
Incidently I've seen several other sets of these flywheels and none were drilled like mine.
All around the rim on the crank pin side were 25, 3/8" blind holes and they said the only way to balance it was to take that much away opposite that they didn't want to do it so I got the crank back.
My solution, clean and tin the holes, pour molten lead into them and tamp it firmly down, then check the balance, I ended up drilling the lead back out of one hole.
Result, lovely and smooth at the bottom end and up to 100mph with a slight tremor around 55 mph.
Incidently I've seen several other sets of these flywheels and none were drilled like mine.