Tale of Two Flywheels
 

What started as a clutch swap turned into a balance issue. The engine has a stock (external) balance flywheel, rotating assembly was balanced. Brought the wheel and the clutch to a shop to check balance. They added a ton of wt to the clutch. Not knowing any better, it was installed and the engine vibrated bad. Informed the shop, and they offered to remove the clutch and rebalance.

I assumed they'd just restore the clutch to factory neutral and knock the weights off, but instead they removed material from an original '65 stock flywheel, removed the clutch wts and then re-added wts...I couldn't believe it when I heard later. I didn't know at first, but when driving the car I knew something was off. Called and was told the flywheel had been modified, I knew that was a totally worng thing to do, so I called them out on it.

This threw off the rotating assembly balance of course. Car goes back to the shop a second time. They had a real stock '75 flywheel on hand in very good condition to replace the '65 wheel. This time I take the flywheel and clutch to my engine shop for a dynamic balance, instead of a static balance.

At this point I have a stock '75 flywheel w/external balance with a neutral balanced clutch. It still has vibrations. It's worse now than with the flywheel and clutch assembly neutral balanced.

I've read on forums that all stock Pontiac flywheels from '64 to '76 have the same external balance. I cannot find any documents that support that claim or any specs on them to check, and now with this other wheel on, I'm finding it hard to believe.

It looked good on paper, but it's not right.

I took the car home last night and there it sits. I couldn't leave it there forever and keep trial and erroring this just hoping it'll work. The engine shop has the bob wt card still from 15 years ago on the 455 build, but according to them it won't help to verify if the '75 flywheel is exactly the same as the '65.

This is a major bummer to my summer, so it's pretty much done. I doubt I'll be made whole by the transmission/driveline shop. They did what they could to fix it after taking it apart twice.

At this point there's only one option, remove the crank and rebalance the works.

This is another lesson on spending money and getting nowhere.

I'm sorry you are going through this because it should have never happened. The complete rotating assembly should have been balanced together and the clutch assembly should have been neutral balanced on it's own. The stock factory imbalance on the flywheel is so little that it is easy to have it internally balanced and have the clutch neutral balanced.

Yes. Should’ve never happened. My understanding of things before this all happened was minimal. Trusted others to check things and it turned into a total disaster. I’m well informed on the procedure and other things now but too little too late.

Well this sure is a poop deal. Fwiw generally changing a factory balanced flywheel with a neutral one won't produce a noticeable vibration. It may be more pronounced with a manual trans though. To further complicate things we've seen aftermarket billet flywheels with a removable weight that has the wrong weight added. Someone figured out they could use an Oldsmobile weight rather than a Pontiac to make things more profitable.

One way of attacking this issue would be to purchase a flywheel with the correct removable weight. Have a shop neutral balance the flywheel with the clutch attached and removable weight removed. Now install the balanced assembly without the weight. If all seems good enjoy. If it still has a vibration install the "removable weight" and hopefully that fixes the vibration. The weight might be able to be installed with only the removal of the inspection cover.

Man that’s a lot of clutch removal/replacement. Sorry you have to go through that.

Just curious what damper you’re using? Sometimes dampers are taken for granted and it’s something to consider about the overall balance.

I’m running a RAM aluminum flywheel and an ATI super damper with a balanced rotating assembly and it’s smooth throughout the rpm range.


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I swapped a factory for factory and it’s bad. That’s what I can’t figure out. It’s been apart 3 times now and I don’t know what to do to correct it. I could try some stuff but this is getting ridiculous.

Do you have the bobweight sheet?

do you have all the parts that were smooth running but maybe worn out to start with?

Just wondering if the original flywheel might have had some holes drilled in it to "neutral balance" the flywheel, before they balanced the rotating assembly? Have you looked at it and compared to the second flywheel?

The driveline shop neutral balanced it. 5 holes in it. What I don’t know is was it a stock balance before they did that or was it already slightly modified. I couldn’t guess.

If starting over with another flywheel step up to a steel aftermarket one.

It’s never overkill when protecting your only 2 feet.

Not sure which year the register size
changed, but it's worth a mention?

"The engine has a stock (external) balance flywheel, rotating assembly was balanced."

So, the rotating assembly was balanced with the external flywheel ON, as it should be?

"They had a real stock '75 flywheel on hand".

Really? An untouched 1975 flywheel? Was it verified untouched?

Hard to believe since your engine ran fine with your original external balanced flywheel, and not so fine with it when it got neutral balanced.
Going back to an external balanced original Pontiac flywheel would make the engine running fine again, i would think.

Yes in 2010 it was balanced with the flywheel and HB.

Yes they had a factory Pontiac wheel on hand. A customer with a 75 Trans Am swapped to a Tremec and did not want it back. Looked very nice. 75 date code. Had the typical 2 factory holes on the back side.

It ran great, then as I wrote before the shop took it upon them selves to balance a flywheel to neutral when it should never have been touched.

Back to a factory balance wheel is what was installed now. It was dynamically checked at a DIFFERENT shop to verify it had the factory balance. The engine shop I used in 2010 did it. Clutch PP was neutral balanced. So in theory it should’ve been close enough to its original configuration.

But it’s not.

Unknowns

1. I don’t know what the imbalance was on the factory 65 wheel. Has the 2 factory holes then 5 more 90* away that neutral balanced it.

2. Without knowin the 65 wheel specs, can’t compare to the 75 wheel specs.

3. Was the 65 wheel tweaked back in 2010 when balanced with the crank? I’m looking into that.

4. What affect is the clutch having in all this? It had all the weights that had been welded on at the driveline shop removed and brought back to factory neutral balance. No extra anything on it.

So yeah. This is a bad deal. Never should’ve happened like this and after 7 weeks the issue has not been resolved. I doubt I’ll be made whole on this. That’s what really sucks and the fact it blew up the end of the car season.

That’s a great question. Not sure at this point but the engine shop may know something or have info on the bob card. May be a way to temporarily ad wt to the 65 wheel to verify its original imbalance.

Maybe I missed it but have you already tried a neutral balanced FW along with the neutral balanced clutch assembly?

The 65 factory flywheel had an imbalance according to the “driveline” shop, but the “engine” shop could have taken a small amount out previously.

Kenth can you share the flywheel balance specs and how they are mapped on the part?

Is this the original flywheel you took out? If so, it looks like someone, probably the people who balanced the engine, drilled holes in it to neutral balance it. Personally, I'd but a new neutral flywheel and try it. I bet that's what the engine is balanced to.

It wasn't Wagamon Brothers, I hope?
https://wagamonbrothers.com/

The balance on the flywheel in the picture is completely screwed up. Everyone involved in the project needs to be replaced with competent people.

If you know the shop that originally balanced the rotating assembly they should be able to tell you if they removed weight from the flywheel to balance the rotating assembly, it's called "standard operating procedure". If they did they need to be replaced, if they can't tell you they need to be replaced.

Plan B since you didn't like my first suggestion, would be to have the engine shop figure out what balance holes they made. Then have the clutch shop figure out what balance holes they made. Report back and we might be able to figure out what's going on.

Sorry you're going through this.

I did my best to try and read and understand everything in this thread. I have to admit, I don't fully understand everything that happened, when and by who enough to make a recommendation that I know will fix it. So, if I was faced with this situation and was committed to make it right, I would do the following. Your probably not going to like this. I would remove the engine and and the crankshaft. Have the crankshaft zero balanced +- 2 grams and verify. That completes the engine. Then I would buy a steel zero balance flywheel and a zero balance clutch. Problem solved. Time consuming and possibly a little expensive, but now it's fixed. Mixing, matching, drilling, bolting , welding, guessing, removing, installing, you may get lucky and hit the right balance, but it may be an even more time consuming exercise than just biting the bullet and doing it all one more time, correctly. I wish you the best. Very frustrating I am sure. I hope you get it.

I was told that the bob weight card does exist at the shop that balanced the engine 14 years ago.

No I have not tried that combo. From what I’ve been reading in other posts, the neutral balance FW may not be that far off from a factory balance FW. Still waiting on what the factory specs were.

It's a series of events that involved 2 clutch sets (Centerforce & McLeod), 2 flywheels ('65 & '75 factory pieces), 2 shops (Wheeler Racing and Midwest Transmission), 3 trans RnRs to date.

Engine was well balanced with the '65 FW and HB by Wheeler Racing. Worked great.

It was assumed that both the '65 and '75 FWs had factory balance. I'm not so sure about that now given the huge difference in behavior.

The PP on the McLeod had weights added and removed 2 times! Could that cause issues? Maybe.

The trans shop tried to neutral balance the '65 FW by drilling into the factory holes and adding 3 more, so I have no clue what they removed vs what was already removed by Pontiac. To this day I don't know what possessed them to modify a flywheel.

To date there's been 4 different FW and PP combos

1. '65 Factory FW with Centerforce PP (factory neutral balance). Worked great.

2. '65 Factory FW with McLeod PP (2 large washers welded to it). Bad vibrations at idle and beyond. FW was not modified at this point. I think they tried to neutral balance the FW/PP combo not knowing it was supposed to have a slight imbalance.

Here's where my car went from a buddies shop to the transmission shop.

3. '65 Factory FW with McLeod PP. This is when they drilled into the FW to neutral balance, then ground off and welded back weights on the PP to neutral balance the FW/PP assembly. This combo had the least amount of vibration of the 3. When I received the car, I was not told they drilled into the flywheel. I assumed they only removed the weights from the PP to restore it's original balance. In a phone call a week later it was revealed the flywheel had been drilled. After a week of arguing with the shop owner about it, the car went back to the trans shop.

4. '75 Factory FW with McLeod PP (all added weights removed). This time it was balanced dynamically at Wheeler Racing. The combo did not produce. Vibration above 2500 rpm and beyond. Worse than combo 3.

It's a guessing game now. Could try the '75 FW with the Centerforce PP Attempting a 5th combo vs. engine/crank removal? The trans can go in and out in a day, the engine work will take way more time and money. So far the trans shop covered 2 RnRs, but that can't go on forever.

Not Wagemon Bros. Was told long ago to stay clear of them.

I think you were warned wrong. My Pontiac engine after them ran very smooth.

I think your first suggestion was fine, it's a matter of time and logistics at this point. The car is home now, so I'm planning my next move.

I agree with the assessment of personnel. I ask questions and I get attitude that implies I'm questioning their work. As I should!

The engine shop said they have the bob weight card, what can be determined from that without the crank out of the engine? I asked if they could figure out what the original FW balance was, I was told no. I'm not savvy with what can and cannot be determined from that info. If it can be determined, how? Don't you need the crank and the bob weights to verify and measure the FW balance?

This is a FW issue that affected the engine. Has nothing to do with who built it.

The engine shop should be able to tell you if it's standard procedure at their shop to remove weight from the balancer/flywheel when they balance a crankshaft. This should be avoided if at all possible, but I've seen many shops over the years practice the bad habit.

If they did remove weight they should be able to identify the holes they made from the recently added holes. The last guys should be able to also. When you know the location of whose holes are where, we might be able to figure out why they were added. When one neutral balances a factory flywheel the majority of weight needs to be removed 180 degrees from the factory balance holes. Your picture looks like the majority of the holes are roughly 90° from the factory holes.

I can clearly see what holes the driveline shop made. If the engine shop drilled holes physical evidence of that was destroyed. I am trying to find out if they did drill it. So far I’ve been ghosted. Will rattle their cage again on Monday.

Driveline shop claims there were 2 holes about 90-100 degrees from the 2 Pontiac holes untouched. They hit those and added 3 more. So good luck figuring out its previous balance.

The two holes from the factory should correspond to 6 inch ounces.

HTH

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.

So that’s where it’s at now. ‘75 FW with a neutral balanced PP. It’s not a good match. I will talk to engine shop Monday that did the original balance with the ‘65 wheel. If you saw the photo I posted you’ll notice the 5 holes are 90-100* from the factory drill holes. Any attempts to zero balance the FW would require holes opposite if the factory ones. The driveline shop claims that there were some drill holes at the 90d position. Right. The lack of specs on the ‘75 FW other than it came off an F Body car (what else) raises doubt that it’s the same spec as the 65 FW. It could be an alternate design different from the typical 65-75 spec. Still waiting for someone to post the flywheel specs from the H-O publication.

Kenth is correct. from the H-O engine book, 6in/oz. is the number. I believe we got that info from a blueprint that Pontiac sent us. The info from the balance shop should clear things up. The question to the shop should be:
Do they routinely balance assuming a zero balance flywheel?
Do they routinely balance with the supplied flywheel (or flex plate) without modifying the flywheel?
Do they routinely modify the flywheel along with the balance job?
Hopefully, the balance card will have a note about the flywheel, and/or the shop owner will be able to respond.

I’d like to the see the published docs from H-O regarding the Pontiac stock FW. Snap a pic and post it. The book is impossible to get so I think it’s important to share. Or PM me then text it to me.

Today others pointed out that the neutral balance attempt on the ‘65 FW is suspicious. In theory, any attempt to zero balance it would need 2 equal holes opposite of the factory holes.more or less. These are 80d off. The driveline shop used a primitive static balancer. I guess I’m not surprised. So many miscues and lack of process. Not acceptable for a driveline shop that uses “expert” on the website. They claim it had a couple holes in that area already. I’ll confirm that with the engine shop. I will ask them the questions as Ken Crochie suggested. The whole idea of a driveline shop balancing a FW is plain wrong. Only an engine shop should attempt that. And only when really needed.

The 75 wheel may not be the same factory spec as the 65. Per Ken C. It could be for a different crank design. So it could cause vibes even if in perfect condition and look similar.

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

Measured the voids of mass removed. Factory wt removed is about 24 grams total or 0.84oz. Radius hole to hole is 5-7/8”. So that’s about 5 oz-in
Assumed a unit wt of cast iron at 4.128oz/in^3.

The modified (f’d up) area lost about 17g total.

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!

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.

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.

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.

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.

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

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.

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

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#.

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

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