841 crankshaft counter weight

Folks have tried to answer the practical aspect of your question so I thought I'd give ya the theory.This will take some thinking. Imagine an engine with a 6 in stroke and a 12 in connecting rod. The crank pin rotates in a 6 in diameter circle 3in up from center and 3in down. Assuming an end view of the crank, when the crankpin is at 9 o'clock the piston is about 11in above the crank centerline because the connecting rod is at an angle. At noon the piston is 12in of connecting rod plus 3in of crankshaft lift or 15in above crank centerline. At 6 o'clock the piston is 12in of connecting rod minus 3in of crankshaft or 9 in above crank centerline. In other words, during the top half rotation the piston moves 4in up and back and in the bottom half it only moves 2in. The crank rotates at a constant speed through the rotation so the piston has to move faster through the top half. On a four cylinder engine the jerk created by the 2 pistons going up does not ballance the corresponding jerk of the two pistons going down so a ballancer is sometimes used. (numbers chosen are totally arbitrary to illistrate my point and are not mathematically accurate)

The ballancer is a box with gear driven offset weights which are timed to the crankshaft. The idea is the offset weights are sized and timed to exactly counterballance the above effect.