Crankshaft Balance

Crankshaft Balance Points : Crankshaft Balance, Harmonic Balancers (Vibration dampers) The effect of lack of balance of a crankshaft multiplies considerably with increase of speed. The static balance of a crankshaft does not ensure dynamic balance, but one can be sure that if the crankshaft it out of static balance any engine is designed to be, the more it will suffer from any lack of balance introduced by renewed of parts which are not equal in weight to those replaced.

Harmonic vibration is a higher frequency movement resulting from twisting and untwisting of the crankshaft. Each piston and rod assembly can exert over a ton of downward force on its journal. This can actually flex (bend) the crank throw in relation to each other.

If harmonic vibration is not controlled the crankshaft could vibrate like musician’s tuning fork or a string type musical instrument. Serious engine damage (usually crankshaft breakage) could result.

A harmonic balancer, also called a vibration damper, is a heavy wheat mounted in rubber to control harmonic vibration.

The balancer in keyed to the crankshaft snout. This makes the damper spin with the crankshaft. The figure illustrates the basic construction of a typical harmonic balance. Note how a rubber ring separates the outer inertia ring and the inner sleeve.

The inertia and rubber rings set up a damping action on the crankshaft as it tries to twist and untwist. This deadens vibrating action. An in the alone figure the crankshaft pulley in often part of the harmonic balance.