Using a Ruler to Test Crank Balance

If you press a steel ruler onto the engine case while the engine is running in neutral you can find out if there is too little or too big counterbalance holes in the crank wheels close to the con rod pin. If you get more in-line ruler motion than when testing it for 90°-off motion then that means the holes are too small.

If you get more fore-aft motion than in-line motion then that means the holes are too big and you need to drill holes into the crank wheels opposite of where the con rod pin is.

Of course rev it up to a RPM that you most often use but don't let the engine rev high for more than a few seconds to prevent damage.

If you are anxious to test and don't have a steel ruler then try it with a 24"/26" bicycle wheel spoke. It's not as good but sometimes can be adequate.