I got wind of this wind from RunRyder. There seems to be some confusion on how to ballance a crand shaft so I would like to add my input.

The correct bob-weight is half of the piston with all its parts and half of the top end of the con rod and all of the bottom of the con rod.

Another way to look at it is to weigh the piston-ring-pin-conrod assembly and divide that weight in half. Add back in 1/4 the weight of the con rod. Now use that number to make a weight on your lathe to fit on the crank shaft pin where the big end of the con rod normally goes. Now ballance this assembly.

Single cylinder engines will NEVER be able to be ballanced completely.

The reason for this is that the piston only goes up and down and any counter weight on the crank goes 'round 'n 'round. The more counter weight on the crank the more you can offset the piston going up and down. So you can offset the up and down vibration. But as you add more counter weight, the motor starts to vibrate side to side. The only answer is to put enough counter weight on the crank so the up and down vibration is equal to the side to side vibration. This way the counter weight will offset half of the up and down vibration while causing that same amount of vibration side to side.

Now, when you mix these two vibrations that are 90º out of phase, you get a circular vibration that acts like it's rotation is opposite of the crank rotation. Just like a smooth running shaft with a weight mounted on the side of the shaft.

The only way to cancell this last amount of vibration is to have a counter rotating weight concentric or near the crank shaft center line. Some motorcycle engines have used this method of vibration control.

Wolfgang