[79 Phoenix]

I know this topic has been discussed before. I have read postings but am still confused. Here's my situation...

1) I have a 76 400 engine that has been mated to an automatic transmission up until now. It has a flex plate on it (see picture) with 4 large holes on one side. I assume these are to balance it.

2) I have had my original 71 GT-37 flywheel off the original 350 engine resurfaced, spacer ring to make it fit smaller 76 register on crank inserted and tacked AND I had it balanced. To balance it, they removed 24 grams of weight by drilling a hole on the back side (not shown).

QUESTION: Can I now use this balanced flywheel with this engine? I'm using the original factory 3 speed trans that came with the car. Should I have them check the balance on the flex plate on the 76 engine and make the flywheel match that?

PS As far as I know, 76 400 engine is stock. Also does not appear to have a harmonic balancer on front--just pulleys

[tom s]

Yes,check the flex plate and balance the flywheel to it.Tom

[Schurkey]

Originally Posted by 79 Phoenix

1) I have a 76 400 engine that has been mated to an automatic transmission up until now. It has a flex plate on it (see picture) with 4 large holes on one side. I assume these are to balance it.

I'm thinking that those holes are the original, GM balancing holes, intended to provide the GM-specified offset weight for the external-balance Pontiac engine.

Originally Posted by 79 Phoenix

2) I have had my original 71 GT-37 flywheel off the original 350 engine resurfaced, spacer ring to make it fit smaller 76 register on crank inserted and tacked AND I had it balanced. To balance it, they removed 24 grams of weight by drilling a hole on the back side (not shown).

"BALANCED" to WHAT SPEC? It should have been factory-balanced to the GM-spec for Pontiac external balance. Was this changed to a neutral-balance spec?

Originally Posted by 79 Phoenix

QUESTION: Can I now use this balanced flywheel with this engine? I'm using the original factory 3 speed trans that came with the car. Should I have them check the balance on the flex plate on the 76 engine and make the flywheel match that?

PS As far as I know, 76 400 engine is stock. Also does not appear to have a harmonic balancer on front--just pulleys

Kinda guessing, but I'm thinking the flywheel is now neutral-balanced but the engine needs the external balance of the stock flexplate. Look at your receipt for the flywheel balance job and see if the thing has been changed to neutral balance.

IF (big IF) this is correct, you either wasted a bunch of money getting the flywheel neutral-balanced, OR you need to correct the balance of the engine, probably using heavy metal which will also be really expensive. Engines are externally-balanced because there's not enough counterweight on the crank to do it internally. Thus the (typical) need for heavy metal unless lightweight internal parts--piston pins, pistons, rods--are used inside the engine.

You might want to buy a stock-style external-balance steel flywheel and sell or scrap the one you have. I would not waste the money modifying an iron flywheel. Modifying it TWICE--from external-balance to neutral-balance, and then back to external balance--is nuts.

[79 Phoenix]

Okay guys thanks... Yes, neutral balanced. I'm not very familiar with Pontiac engines...Guess this is part of the price for learning.

[79 Phoenix]

Originally Posted by tom s

Yes,check the flex plate and balance the flywheel to it.Tom

Again, I'm putting a flywheel off the original 350 (with M13 3 speed)on a 76 400 which has always been an automatic. So the 350 flywheel can be match balanced to the flex plate originally on this 400? This should make this flywheel correct for this engine?

[Schurkey]

Originally Posted by 79 Phoenix

So the 350 flywheel can be match balanced to the flex plate originally on this 400? This should make this flywheel correct for this engine?]

Originally Posted by Schurkey

Modifying it TWICE--from external-balance to neutral-balance, and then back to external balance--is nuts.

A piece-of-crap iron flywheel should be deposited in the scrap bin.

Get a steel flywheel that is external-balanced to suit Pontiac engines.

[tom s]

If the engine is not going to be raced and the flywheel has been surfaced and will get matched to the flex plate I would just run it.Tom

[79 Phoenix]

Originally Posted by tom s

If the engine is not going to be raced and the flywheel has been surfaced and will get matched to the flex plate I would just run it.Tom

That's what I'm going to do Tom. Thanks.--Kim

[79 Phoenix]

Originally Posted by Schurkey

A piece-of-crap iron flywheel should be deposited in the scrap bin.

Get a steel flywheel that is external-balanced to suit Pontiac engines.

Well it did pretty good for having been on the road for 21 years... So hopefully it will be fine with my 76 400...not much different power-wise than the original 350.

[79 Phoenix]

I'm using the original re-surfaced flywheel from my 71 GT-37 350. I'm using a spacer ring because i'm bolting it to a 1976 400 crank with smaller register.
The flywheel has been balanced to match the balance to the original flexplate on the 400 (it was an automatic car).

QUESTION: Is it true that the flywheel bolts will line up only one way onto the crank so the balance will be correct?

[johnta1]

Yes.

[79 Phoenix]

Okay thanks! I thought so but wanted to make sure before I finish putting this together..