Thread: The old balance problem

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O.K, so I figured out why my 350 is a vibrator, I put a 305 crank in it not realizing at the time that they balance differently. I have an early harmonic balancer on it and a standard trans flywheel. It's not unbearable, but annoying. I hate the idea of pulling it and replacing the crank and wonder if anyone has ideas about using a fluid damper to help smooth it out. Thanks..

nope re balance is all that will fix it. and if you leave it, it's going to shake itself to death. heavy wear on all bearings, in a short period of time

Stay with Matt on this. WHen you look at the crank casting numbers------same. But reciprocating mass is lighter. Balancing (mass rotation) "sees" 50% of the upper weight (rod small end, piston, rings, wrist pin) and 100% of rod throw mass (rod big end, rod brgs, and crankshaft throw) It wouldn't appear to be a big deal but it is. Sad part is, I have found more main brgs wiped out and junked worse than the rod brgs and crankshaft rod throws. Go figure. Balance it to your app. Harmonics under this condition will cause a bunch of grief.

That is definitely not what I was hoping to hear, but thanks for the info.