Why a Counterweight Crankshaft?

Aug 16,2023

The VW air-cooled engine is designed for low RPM, low power output and high mileage use. When used that way it gives many years of trouble free service with little or no wear. However, the higher the RPM, power, or the quicker the acceleration, the more the centrifugal force bends the crank at the center main. This bending force occurs because the two center rod journals are on the same side, putting all the weighted forces on one side of the crankshaft. This pounds out the case at the center main saddle, plus makes the pulley and flywheel run out often damaging the case at the pulley end.

It also puts the rod into an acute angle, one of the things, which drives wrist pin keepers out of the piston. If this bending gets too bad it can cause rod breakage or even the loss of a flywheel. Berg counterweights balance this effect so the crank not only stays straight; it also rotates on a film of oil, as it should. Crankshaft strength is also increased with the addition of the counterweight. This provides longer case, rod, piston, cylinder and bearing life.

Crankshaft

Crankshaft: Types, Functions & Examples

None!