Broken crankshaft on 327/350 shp

[Steven B.]

Re: Broken crankshaft on 327/350 shp

I'll talk to the pilot.

I have heard of balancer problems causing crank failure too. A look to see if the ring has slipped would be a good idea.

Tom

Interesting you mention that Tom. Two years later I replaced the balancer. The ring had slipped.

[Bill M.]

Re: Broken crankshaft on 327/350 shp

Bill-----


I agree. In fact, if it were me, I'd replace the balancer on the rebuilt engine. There are possible problems with balancers that are very difficult to discern with visual inspection. It's just not worth trying to re-use this balancer, in my opinion, especially considering it's likely over 40 years old. In fact, I'd use a NEW GM balancer and not worry about the lack of "fins" on the rear of the balancer hub. I'd also DEFINITELY have the entire reciprocating assembly, including new balancer, custom-balanced. NEVER put an engine together without doing that.

One curious thing here: both of the engines reported on here, the L-79 and L-82, have FORGED cranks, not cast. So, based on the small sampling of broken cranks reported on here, we have two broken forged cranks and no broken cast cranks.

Years ago someone told me that NASCAR engines used cast cranks because they were better able to hold up to the sort of stresses that NASCAR racing imposed on them. I never confirmed if that was true, though. Plus, this was years ago, so even IF they did once use cast cranks, that wouldn't necessarily mean they still do.

I've heard that forged cranks "ring" and cast don't, so maybe there is more inherent damping in the cast cranks.

As rubber ages, it gets harder. The natural frequency of the damper might rise to an ineffective frequency as a result. I think a new damper is a great idea.