About Balancing Engines for Less Vibration
And My Excel Crank Balance Calculator

An imbalance in the crankshaft in relation to the reciprocating weight of the upper end causes vibration and a loss of power. Making sure your engine is balanced correctly is essential, especially if you are modifying the engine to work in a different RPM range than what it was designed for. Using a lighter wrist pin can help if the vertical forces are too much.

Click here to read why I don't recommend using the balance factor method.

Click here to read of my tests which helped me develop my crank balance program.

Below are two useful online calculators. The second one may be needed if you use two different sized drill bits in the same hole with the largest bit only drilling a portion of the full depth. You can do that if you need a certain amount of weight removed but you don't have the right size drill bit.

centrifugal force calculator  (don't enter linear speed. change m to mm, change kg to grams, change N to lbf)

steel weight calculator  (multiply kg by 1000 to get grams)

Here is a picture of my crank assembly with an additional balancing hole just above the conrod pin. The 6 blue holes are lightening holes (although I wouldn't recommend any more than 4 if the bike is for street use). The blue is foam filling half the hole. The ends of each hole were later filled with JBWeld. I used foam just to reduce the amount of expensive JBWeld used. The conrod hole and two factory balance holes are already filled with JBWeld for increased crankcase compression (although the change is very small).

You can drill extra balance holes with any good electric drill although it's a bit tough. Much easier to take it to a machine shop and let them put it on a drill press. Also the holes can be drilled at the TDC location of the crank wheels without even taking it out of the crank cases. Just put duct tape on the crank wheels (after cleaning them with alcohol) to keep metal shavings from going into the crankcase, and then keep the crank in correct position by using vise grips on the primary gear above and below where it meshes with the clutch gear. You can measure from halfway through the angled tip and mark the drill bit at the correct distance with black electrical tape. That way you have a visual reference while drilling.

Click here to read more about my spreadsheet which can be used to calculate the size of counter balance holes needed in any single cylinder crank.