[PAUL K]

Originally Posted by AG

The bolt pattern offset was used so that the flywheel could only be oriented one way to maintain stock balance.

That's the correct way to do it.... If you can believe it, Chevrolet missed that memo.

Another thing most folks don't realize is that crankshaft wobbling around in there can wipe out main bearings in little time.

[Kenth]

Originally Posted by mgarblik

Thank you for clearing that up. My information came from an old GM film that showed the build process of Pontiac engines at the plant. I was almost sure I was watching the final dynamic balance being performed on rotating engines and just small amounts of finish balance material being removed externally. I remember thinking that was really bizarre as that would sort of marry the flywheel to the crankshaft which would be wrong. How in the world did they drill cast iron counterweights on an assembled engine without leaving metal in the engine? Amazing!

This may be the film?
9.45 into it they describe the balancing of the assembled block.

https://www.youtube.com/watch?v=9LuXf6gJ-jg

[mgarblik]

Originally Posted by Kenth

This may be the film?
9.45 into it they describe the balancing of the assembled block.

https://www.youtube.com/watch?v=9LuXf6gJ-jg

I am not sure if that's the same film. Some of it looks familiar because I remember being surprised by the number of women working the engine line. This film clearly shows and the narration states the balance involves removing metal from counterweights and all engines get this treatment. It also shows cranks being installed with major balancing completed before installation as the large balancing holes can be seen before the crank is lowered in he block. For some reason, I think the film deep in my memory was about 30 minutes long, not 10. This may have been an edited version. Also, my foggy memory seemed to to remember some manual transmission engines getting the final balance with the flywheels in place. This film showed all auto trans ones in that section. In any event, your explanation makes much more sense and would allow for much greater interchange without problems later in the engines life. Thanks for finding that.

[scott70]

Well this thread has helped me out on somewhat understanding and to ask questions. I just happen to had a new steel billet flywheel and clutch at the machine shop to check for balancing per McLeod own recommendations. Just went to pick them up and asked if he had balanced my motor ( 5 years ago) with the oem flywheel. He tried to look it up quickly but didn’t find anything. He asked if I still had the oem flywheel I said yes it’s still in the car. He said bring it in and they will check it and match it to the new flywheel if need be. So I guess I’m yanking the muncie out a little earlier than I had planned. The new McLeod flywheel was very close itself to neutral balance and by clocking the PP on it got the whole thing balanced but that might be all out the window now.

[AG]

You'll be able to tell if your stock flywheel is neutral balanced or has the factory balance and hopefully it is neutral balanced.

[MPKind]

A more general question. How many grams of mass removal does it take to be noticed via vibration? 10g , 30, 100? How sensitive is the motor given some say a zero balance flywheel wouldn’t be noticeable vs an external balance that has nearly an ounce of material removed.

[Kenth]

The difference between a neutral and a factory Pontiac flywheel/flexplate is about 6 inch-ounces, 170.1 grams, wich if not compensated for will show up as a pronounced vibration over 2500 rpm.

I would guess a neutral flywheel/flexplate with an (1) oz removed would vibrate less. I´m not a candidate for testing this, i would stick to the factory parts.

FWIW

[MPKind]

Finally got under the car and flipped the inspection cover open. The factory drill hole pattern is quite different than mine. I have the typical 2 holes close together. Same size. This 75 wheel has 2 hole far apart. One big one small. Cast in 75 but belonged to a 76 is my guess. So that’s good news that they are differently balanced. Get the correct stock flywheel and maybe it’ll come back. A real stock one may pair the best with it. The original was 38#. I see most after mkt ones are around 32#.

[MPKind]

Found a summary of crank variations. Starting in 75 thinner weights showed up. This would require an alternate stock balance flywheel different from the common 65-75 wheel.

Who knew?

http://www.pontiacpower.org/PontiacCranks.htm

[mgarblik]

I mentioned some of that info in post #32. So I was not completely wrong fortunately.

[MPKind]

Originally Posted by mgarblik

I mentioned some of that info in post #32. So I was not completely wrong fortunately.

It’s what made me get under the car and check. Thanks for the info. Clearly the Pontiac Power guy had done detailed research on cranks.

[lust4speed]

This reads about the same as following the pea moving around under walnut shells. I probably missed it but most shops in my area zero balance cranks for a performance build. It seems that the assumption was made that the crank was still needing the 6 inch ounce external balance, but the vibration indicates that a stock flywheel is causing problems.

There were only two choices that should have been made by the original builder - either stock balance retaining the external balance or a full internal balance requiring a neutral balanced flywheel. If a presumed good external balance flywheel vibrates, then the only other choice should be a neutral balanced flywheel.

[MPKind]

This was engine was balanced internal front external rear. Same as a stock Pontiac with a factory 1965 38# wheel. Several poor decisions by a shop that claims to be experts at driveline systems. You couldn’t make it up.

[scott70]

Originally Posted by AG

You'll be able to tell if your stock flywheel is neutral balanced or has the factory balance and hopefully it is neutral balanced.

Just got it out,, heading to the machine shop

[AG]

That looks like a factory cast flywheel for a 455 with an 11" clutch and stock factory balance.

[KEN CROCIE]

MP: Tried to PM you but the last 2 PMs didn't show up.
Remove the PP and start the engine. check for vibration.
I it vibrates you MAY have found the problem.
If it vibrates less. or the same, you need to have as rebalance. Buy a new 30# steel. zero balance factor FW and prepare to rebalance.
If it's smooth, buy a new pressure plate.

[scott70]

Originally Posted by AG

That looks like a factory cast flywheel for a 455 with an 11" clutch and stock factory balance.

Yes it’s the original flywheel..So is this flywheel neutral balanced? I’m sure they will figure it out and make the new flywheel/ clutch kit like it’s supposed to be. Don’t need any vibrations.

[MPKind]

Originally Posted by MPKind

This was engine was balanced internal front external rear. Same as a stock Pontiac with a factory 1965 38# wheel. Several poor decisions by a shop that claims to be experts at driveline systems. You couldn’t make it up.

Originally Posted by scott70

Yes it’s the original flywheel..So is this flywheel neutral balanced? I’m sure they will figure it out and make the new flywheel/ clutch kit like it’s supposed to be. Don’t need any vibrations.

The OE wheel is what you need to use. The engine is balanced to it. Have it resurfaced and ask the engine shop to check the PP for neutral. Likely it’s good but you never know. In theory you can clock the PP in any position. The shop may determine the optimal position.

Since Midwest Trans f’d my flywheel I no longer have a balanced set. And they claim it had holes in addition to the factory ones. So that’s another bummer.

I’ll likely have to pull the crank and start over.

[scott70]

Originally Posted by MPKind

The OE wheel is what you need to use. The engine is balanced to it. Have it resurfaced and ask the engine shop to check the PP for neutral. Likely it’s good but you never know. In theory you can clock the PP in any position. The shop may determine the optimal position.

Since Midwest Trans f’d my flywheel I no longer have a balanced set. And they claim it had holes in addition to the factory ones. So that’s another bummer.

I’ll likely have to pull the crank and start over.

The engine shop rebuilt and balanced the motor 5 years ago so I’m not exactly what they did.

[mgarblik]

Chances are the engine shop that balanced the crank would know "how" they balanced it. Most shops have a standard way they balance various crankshafts by application. If a customer presents a Pontiac crankshaft for balance, most shops would be aware of the slightly different way "partial" internal balance crankshafts are done. They would have asked the customer if they wanted a "full internal balance using a neutral balance flywheel", or a stock balance. At my school, we like to do a full internal balance because it opens you up to any one of many options for flywheels and pressure plates in the future. If we do a stock balance, we balance with the flywheel only added to the rear, no pressure plate. Once that's good, we bolt on the pressure plate and spin it again to see if the balance remains correct. Then if needed, fine balance the pressure plate with tiny magnets to get it just right. Mark the location, weigh the magnets, switch the magnets to washers and weld them to the pressure plate. Good quality pressure plates generally don't need any attention other than a check spin.