How do you know if a Harmonic Balancer is bad
 

This motor is on a stand at this time it is a 1991 365 hp.
Put Balancer on lath and it shook really bad.
Put the Balancer of a 1988 330hp on lath and it did not shake very much at all.

My Question is how do you tell if a Balancer is bad.
I belive they are not neutrally balanced but why does one shake so much and the other does not.

Are these balancers interchangeable,although they are on two totally different cranks?

I guess not ,maybe the answer on that!!
But there is always hope!!

Any help here would be great.

Nobudget!!!

as far as i know balancers are not interchangeable. dont; hold me to it but i don't think tehy are. an 88 engfien is probably a gen iv and a 91 might be a genv so that mighta ccoutn for the differences.

396,402,409,427 are all "internally balanced" crankshafts. This means that the flywheel and harmonic damper are neutral balance.

454,502 are all externally balanced, meaning that the flywheel and harmonic damper have a slug of weight on one side.

Tuner motors are either externally or internally balanced depending on the crankshaft. You can get a pretty big stroker crank and get it internally balanced, but it costs more and has big honkin counterweights on it.

Motors using factory GM components are balanced properly using the correct flywheel and harmonic damper, but if you have put in nonstock rods or pistons the whole assembly including the flywheel and balancer will have to be taken to the balancing man together (if you have an externally balanced motor). If you have an internally balanced motor, the flywheel and harmonic balancer do not need to accompany the other parts to the balancing man.

A 454 damper from a 330 and a 365 I would think should be identical. They will also both be "unbalanced" on a lathe, since the motors are both externally balanced.