Originally posted by dameetz
I don't fully understand it. Can you explain it in details and make an example? And how do you actually balance it ie: do you put on flat table and see whether the crank pin stays at upright position or is there any other better method?
What Edward measn by 52 - 58% balance is as follows.
If the Piston/Conrod and pin weigh say 100g then the ideal weight for the crankshaft is between 52 and 58g.
To get that ideal weight you either remove or add material to the rear section of the crankshaft (the counter-weight). To balance the crank properly the crank should always stay perfectly still when the pin is sitting at Top Dead Center postion. To get this you need a special jig made up that holds the crank at both ends on its center line (similar to a propellor or wheel balancing tool).
if you have to add weight you need to select a heavy material like brass and insert it into the weight (like drilling a hole and squeezing a piece of brass bar into the hole). The process is not easy and I would suggest experimenting with old engines.
It will take time to learn where to take the material off/add material too any given crankshaft to get the ideal weight while achieving the desired balance without weakening the crank at any point.