Technical Help - SBC - Horrible Vibration - Wrong Harmonic Balancer?

Maybe a hi-jack --- but here I go

I've got kind of the same issue,

Sold my 1966 Vette but with a "balanced" 1979 one piece rear main seal 350 SBC. I kept the 327 non original engine because it had been balanced with the fly wheel etc. even though I don't think it mattered.
So now I need to supply a used salvage yard flywheel and exchange clutch and PP for the buyer. Do I look for a specific flywheel or will any "generic" SBC flywheel work on a 1979 SBC 350?

Movin/on

 

What do you suggest?

Rich

 

I'd look at the flywheel/flex plate and make sure its not a 400.
Change the balancer to the correct one, then see what you have.

You have multiple visual confirmations that the balancer is for a Sbc 400. If you are certain that you do not have a 400 then its the wrong part, and most likely the cause of your vibrations barring other issues that may or may not be there.

I don't see what pulling the wrong one and then running the engine without any balancer will tell you when you compare the results. You can't make a decision on any findings because what you'll be seeing is the same engine still out of balance, but only with a different imbalance. Might be fun to see IdK?

 

Any core from a pre-'87 SBC should do, except from a 400 (has extra weight in one place).

 

Isn't there a large and a small flywheel? And I think some of them are drilled for different sized pressure plates too.

You can buy a new replacement pretty reasonably. You might want to look at that.

 

Yes, but the guy who posted was just looking for an acceptable core to return, if I read it correctly. It is still early here.

If not then yes, it will have to be the "correct" one. Yes, replacement ones, new, are pretty inexpensive.

There are 153t and 168t ones, and different pressure plate bolt circles.

The quickest way to tell is the starter bolt pattern, if using an OEM starter. Staggered, straight across, or three bolts back to the bell housing.

 

Sorry to hijack a question posed to someone else, but you should back track. Eliminate all guessing. Ignore which balancer/flexplate you have for a minute. Go back to pulling your pan, check the casting number on your crank. That is going to telling you what the crank is(if anyone put a 400 crank in for some reason), then work your way out based off that.

I just did a similar inspection with a stroker motor I recieved and wasn't getting a response on which balance it needed(int/external). Pulled the pan to find stock 305/350 crank. Can't argue with proof in your hand. Takes unproven info possibly passed on buy multiple previous owners out of the equation.

Back to the topic, Once you know which balance it needs based on the crank then you can get a replacement balancer(and flexplate if yours is weighted).

 

The flexplate did not have any added weights.

I replaced the harmonic balancer with a new one for a 305.

The engine now runs smoo000000oooth.

Thanks guys.

Rich

 

Good deal

 

Beat me to it. I was about to suggest the flexplate as being incorrect. I upgraded my externally balanced 350 to an internally one and upgraded to a neutral flex plate.

 

If that got assembled with a 400 balancer, I would question a lot about the engine. Try a 350/ 305 balancer, you'll have to find TDC and retime the engine to ensure the balancer, timing tab are true.

 

might have been why it was sold....

 

Makes ya wonder, doesn't it?

Rich

 

I saw one BBC in an OT Camaro with the same deal, unreal vibration. The damper was put on by brute force, the front snout of the crank was bent. I say you got off a bit easier.

Bob