[mgarblik]

Thank you for explaining the situation again more completely. I think I understand better now. My suggestion from here which would be fairly easy, is to get a good used flywheel from a 1965-1972 same displacement engine and put it on the engine with a pressure plate that has been zero balanced. IMO, that's your best chance of getting back to what you had 14 years ago when everything worked properly. The 1975 flywheel may have been matched to the lighter crankshaft Pontiac was just phasing in at that time. Things get a little confusing in that time period. Pontiac narrowed the counterweights a little in that period and the crankshafts were a little lighter. They also changed the pilot diameter on the crankshaft/flywheel in that time period. If there was some way to verify the crank was balanced with the old 1965 flywheel and harmonic balancer and these parts were NOT modified to get the proper balance, a replacement used flywheel from that vintage should be close enough to operate properly. The complicated issue is from the factory, the final precision balance was achieved after the engine was assembled and the flywheel was installed. The factory would spin the rotating assembly at a low speed and take measurements. Then a final balance would be achieved by removing a little extra metal from those giant divots in the flywheel. So essentially the born with flywheel was matched and mated to the crankshaft. Made for a smooth engine but caused some trouble in service later when parts needed to be replaced. But it was only a finish balance. The small mismatch should not cause terrible vibration.

[Kenth]

Originally Posted by mgarblik

The complicated issue is from the factory, the final precision balance was achieved after the engine was assembled and the flywheel was installed. The factory would spin the rotating assembly at a low speed and take measurements. Then a final balance would be achieved by removing a little extra metal from those giant divots in the flywheel. So essentially the born with flywheel was matched and mated to the crankshaft. Made for a smooth engine but caused some trouble in service later when parts needed to be replaced. But it was only a finish balance.

Wrong.

The final factory balancing, with a fully assembled block and flywheel/flexplate, was achieved by removing metal from the crank counterweights.
The flywheels and flexplates were all the same, and this for NOT causing problems when these parts needed to be replaced.

And, If you were to buy a new flywheel from Pontiac back when new ones were available you would get a 9779232, same for all 1965-75.

FWIW

[mgarblik]

Originally Posted by Kenth

Wrong.

The final factory balancing, with a fully assembled block and flywheel/flexplate, was achieved by removing metal from the crank counterweights.
The flywheels and flexplates were all the same, and this for NOT causing problems when these parts needed to be replaced.

And, If you were to buy a new flywheel from Pontiac back when new ones were available you would get a 9779232, same for all 1965-75.

FWIW

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!

[PAUL K]

I'm no expert but always thought the crankshafts were balanced by the holes drilled in the counterweights that were figured out by the engineers. Crankshafts were made to a specification and weight. All the holes were machined in a specific location, size and depth to meet the Pontiac desired bob weight. I know a lot of 103 cranks have the same size holes in them and in the same location. All the SD-455 cranks I've seen are in a different area of the counter weight and sized different compared to the 103's.

I'd like to know more as the factory assembly techniques always amazed me. I'm also curious why they needed the slight offset in the flywheel.

[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.