Okay. I noticed an engine vibration in my Cutlass (just bought it). It's a 350. New flex plate, new SFI harmonic balancer...basically, whole new engine, nothing used accept for the block and crank.

I noticed a vibration as the RPM's grew (felt like bad pinion angle). The guy I got it from did not know what it was; he built it, never drove it and then sold the car to me.

It did it in neutral sitting in the garage as well as driving. I decoupled the converter from the flywheel to spin the motor to see if it would still vibrate... it still did, just not as bad.

When I reconnected the converter and bolted it all back up, the car hardly vibrates any more at all. It does a tad, but once the motor winds out...smooth as butter all the way to redline.

What do you guys think? Sould I try clocking the converter in different positions to see if it goes away all together? Get a new fly wheel? Hmmm....

 

I don't see any responses -- did you ever do anything else?

I'm having the same issue with a '67 330...just had the motor rebuilt, only thing new internally was a set of matched & balanced pistons. Everything else was machined and re-used.

It's a 330/2, so the balancer is solid metal and I reused it. I replaced the flexplate with an SFI from Olds Performance.

Bad vibration that's noticeable at idle, get worse as the revs go up through 1500-2000, then it smooths out a bit above 2000. Then you get the same bad vibration as revs come back down through 2000-1500 on decel.

I'm going to try re-cloking the torque converter on the flexplate before I pull the trans or engine. Any other suggestions?

 

Was the flexplate internal or external balance?

 

if the avatar pic is his car thats now jeffrois car (CO member)

maybe he will chime in on if he has any engine vibes

 

I just found out about internal and external balance and that was the first thing I thought of.That and the torque convert may have been balanced with the crank,got put on the engine wrong,than when you disconnected it and reconnected it you put it back right.Long shot but possible.If you take apart again check for marks on the fly wheel and converter.
railguy

 

The flexplate is external balance. The more I read, the more I think the TC must also be balanced and I have it out by 120 or 240 degrees. At least I hope it is that simple. Am going to try that in the morning.

 

This thread is old.

 

Torque converters are neutral balance.
The crank, balancer and flexplate need to match (internal vs external balance) in order to have a good balance. The new flexplate may have a different weight than the previous one, even though it is correct for your application. All Olds (that I'm aware of...) are external balance. Changing the pistons - even though they are matched to each other - most likely changed the bob weight, which threw off the balance some more.

One test would be put the original flexplate back on, see what happens. If it's better, then you'd need the rotating assembly balanced by a machinist with the new flexplate.

Usually skipping the balancing at the machine shop isn't a big deal. Big vibrations come around when there's a mismatch, like when I inadvertently put an external balance flywheel on an internal balance ford 4.6.

Andy sells both internal and external balance 330 flexplates. Did you get the right one? External balance have a large curved weight on the rear of the flexplate. Compare with your original.

 

I got the external balance flexplate. The original one in the car had a curved weight, and the SFI one from OPP had a piece of straight steel welded to it in roughly the same location on the plate.

I tried the other two positions of the TC to flexplate today and drove it on both positions. Little to no difference in the vibration.

I guess my next move is to remove the tranny and try the original flexplate to see what happens. Major PITA, but I can't think of what else to try.

Could it be a problem with the transmission itself? Something that developed while the car sat for a few months without a motor?

 

Was there a brand on the flexplate? Given that it's a lightweight design, I bet the rotating assembly needs to be balanced with it. Just my hunch. PITA at this point, indeed.
For a tranny to cause a shake like that, it would have to be tearing itself to pieces.