G.M. lab test sheets on Corvair Harmonic Balancer development.

The basic concept is that if there is more than 1/2 degree twist vibration (torsional vibration), the crankshaft will eventually fail by cracking. The goal of a good harmonic balancer design is to minimize those vibrations to less than 1/2 degree at the problem r.p.m. areas.

special problem areas for corvair

Note: o.t. means wide open throttle. 'closed' means closed throttle. #6 means 6th order of vibration. #3 means 3th order of vibration.

"safe" limit of twist: (1/2 of a degree of the crankshaft)

'balancer tuning frequency in hertz (cycles per second)

Ideal frequency of 222 hz. (208 to 238hz "safe" range)

We were able to adjust the rubber compound to the 'ideal' 222 hz. freqency by experimenting with amounts of additives.

An added benefit to reducing rotational vibration of the crankshaft is that unwanted vibrations to the distributor, oil pump, and cam shaft are minimized. This should result in a longer lasting, quieter engine. I imagine that the gears connecting crankshaft to camshaft and to the distributor drive gear will wear better with proper crankshaft dampening.

Our own testing of used GM harmonic balancers has shown that as the factory rubber begins to harden with age and temperature, the tuned frequency of the harmonic balancer increased as much as 26% with the unit still appearing to be intact and serviceable. A look at the test data above reveals that if a balancer started out at 220hz when new, an increase of only 10% will put it at 240hz which is the 1/2 degree crankshaft twist safe limit. One might conclude that many apparently serviceable used factory harmonic balancers no longer are capable of protecting against excessive radial (twisting) crankshaft vibration.