# How screwed am I?



## wooftfd (Apr 6, 2021)

Changing out the original 3 speed manual for a Tremick TKX in my 64, stock (rebuilt 10K ago 389), externally balanced...
The machine shop chucked up my flywheel crooked, 9/1000 out of plane, to fix what they did, had to take about 11/1000 off.
Now theres a vibration at 2000RPM... Any ideas on how to fix this? Should I just take the motor out, re-balance it?
Did Pontiac balance every engine on the line? Did they have a stack of flywheels, different weights, and grab whatever the particular engine needed to make its specific balance?
I have another used flywheel, might it be closer in balance then what I have now?


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## armyadarkness (Dec 7, 2020)

All of this sounds very odd. Why would you chuck up a flywheel, instead of replacing it for $80?

Are you sure that your vibration is that? And not driveline angle? Have you checked driveline angle?

Did you shorten your driveshaft? What crossmember did you use?

Was the vibration always there?


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## armyadarkness (Dec 7, 2020)

BTW, if my flywheel was screwed up, Id pull the trans and bellhousing as one piece, replace the flywheel, and put it back together.


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## Jim K (Nov 17, 2020)

External balance usually involves the pressure plate as well as the flywheel (I know mine did with alignment marks provided to keep the pressure plate/flywheel in the same configuration). When you installed your Tremick I am presuming you had a new pressure plate/clutch disk to install with it?
If you did install a new pressure plate and still have the old one, then look at the old one for any marking that would have aligned it with the flywheel.
If your flywheel was part of the original balance and was .009" out of plane for that 10K miles then all the internal parts/front damper were matched to that.
As I understand it, Pontiac did a "hybrid" external/internal balancing. Their engine assembly lines had to balance rotating assembly's together as a set before assembly in the block. While none of this answers your questions, I've always been told that once the rotating assembly is balanced, those parts are "matched" together and changing anything upsets that balance match. You can try other flywheels but it will still be hit or miss. A lot of it might depend on how close the machine shop took their balancing. Some shops provide a closer to "zero" tolerance than others.
Just my two cents..


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## wooftfd (Apr 6, 2021)

armyadarkness said:


> BTW, if my flywheel was screwed up, Id pull the trans and bellhousing as one piece, replace the flywheel, and put it back together.





armyadarkness said:


> All of this sounds very odd. Why would you chuck up a flywheel, instead of replacing it for $80?
> 
> Are you sure that your vibration is that? And not driveline angle? Have you checked driveline angle?
> 
> ...


They said the surface had a couple of hot spots, and wanted to just clean it up, but didnt get it square when they did it, so it was machined off plane. Once they figured that out, they re-squared it up, but had to take off more material to do that. There is a vibration now thats new, without the clutch installed, engine and flywheel only. In order to change the flywheel out, doesn't the entire rotating assembly need to be re-balanced with the new flywheel? 
Yes, had to shorten the driveshaft, and re-used the stock crossmember, jut move it back 1 inch.


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## armyadarkness (Dec 7, 2020)

So that's very informative info on the process... but as you mention, it's presumably irrelevant, once an engine is rebuilt?


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## wooftfd (Apr 6, 2021)

Jim K said:


> External balance usually involves the pressure plate as well as the flywheel (I know mine did with alignment marks provided to keep the pressure plate/flywheel in the same configuration). When you installed your Tremick I am presuming you had a new pressure plate/clutch disk to install with it?
> If you did install a new pressure plate and still have the old one, then look at the old one for any marking that would have aligned it with the flywheel.
> If your flywheel was part of the original balance and was .009" out of plane for that 10K miles then all the internal parts/front damper were matched to that.
> As I understand it, Pontiac did a "hybrid" external/internal balancing. Their engine assembly lines had to balance rotating assembly's together as a set before assembly in the block. While none of this answers your questions, I've always been told that once the rotating assembly is balanced, those parts are "matched" together and changing anything upsets that balance match. You can try other flywheels but it will still be hit or miss. A lot of it might depend on how close the machine shop took their balancing. Some shops provide a closer to "zero" tolerance than others.
> Just my two cents..


the flywheel was ok untill they machined it, now theres a vibration with, and without the clutch, and tranni in... Yea, my understanding too, nad the engine rebuilder confirmed he balanced it as a assembly, flywheel on. The old clutch did have a weight welded in, but the builder told me that was because it was out of balance, and the weight was to bring it back to neutral.


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## wooftfd (Apr 6, 2021)

armyadarkness said:


> So that's very informative info on the process... but as you mention, it's presumably irrelevant, once an engine is rebuilt?





armyadarkness said:


> BTW, if my flywheel was screwed up, Id pull the trans and bellhousing as one piece, replace the flywheel, and put it back together.


In order to do that, I'm going to have to re-balance the engine with the new flywheel, right?


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## wooftfd (Apr 6, 2021)

wooftfd said:


> In order to do that, I'm going to have to re-balance the engine with the new flywheel, right?


Or were all flywheels the same spec?


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## wooftfd (Apr 6, 2021)

wooftfd said:


> Or were all flywheels the same spec?


I have another flywheel, part number 8621677


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## wooftfd (Apr 6, 2021)

Jim K said:


> External balance usually involves the pressure plate as well as the flywheel (I know mine did with alignment marks provided to keep the pressure plate/flywheel in the same configuration). When you installed your Tremick I am presuming you had a new pressure plate/clutch disk to install with it?
> If you did install a new pressure plate and still have the old one, then look at the old one for any marking that would have aligned it with the flywheel.
> If your flywheel was part of the original balance and was .009" out of plane for that 10K miles then all the internal parts/front damper were matched to that.
> As I understand it, Pontiac did a "hybrid" external/internal balancing. Their engine assembly lines had to balance rotating assembly's together as a set before assembly in the block. While none of this answers your questions, I've always been told that once the rotating assembly is balanced, those parts are "matched" together and changing anything upsets that balance match. You can try other flywheels but it will still be hit or miss. A lot of it might depend on how close the machine shop took their balancing. Some shops provide a closer to "zero" tolerance than others.
> Just my two cents..


the flywheel was ok until they screwed up the machining on it, now the entire engine is out of balance, and I'm uncertain if I can just replace the flywheel, or is every stock flywheel different weight?


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## wooftfd (Apr 6, 2021)

Jim K said:


> External balance usually involves the pressure plate as well as the flywheel (I know mine did with alignment marks provided to keep the pressure plate/flywheel in the same configuration). When you installed your Tremick I am presuming you had a new pressure plate/clutch disk to install with it?
> If you did install a new pressure plate and still have the old one, then look at the old one for any marking that would have aligned it with the flywheel.
> If your flywheel was part of the original balance and was .009" out of plane for that 10K miles then all the internal parts/front damper were matched to that.
> As I understand it, Pontiac did a "hybrid" external/internal balancing. Their engine assembly lines had to balance rotating assembly's together as a set before assembly in the block. While none of this answers your questions, I've always been told that once the rotating assembly is balanced, those parts are "matched" together and changing anything upsets that balance match. You can try other flywheels but it will still be hit or miss. A lot of it might depend on how close the machine shop took their balancing. Some shops provide a closer to "zero" tolerance than others.
> Just my two cents..


My understanding is the shop that did the rebuild (prior to me buying the car) is a serious shop, and builds high end racing engines... The owner assured me it was within a gram or so of neutral


Jim K said:


> External balance usually involves the pressure plate as well as the flywheel (I know mine did with alignment marks provided to keep the pressure plate/flywheel in the same configuration). When you installed your Tremick I am presuming you had a new pressure plate/clutch disk to install with it?
> If you did install a new pressure plate and still have the old one, then look at the old one for any marking that would have aligned it with the flywheel.
> If your flywheel was part of the original balance and was .009" out of plane for that 10K miles then all the internal parts/front damper were matched to that.
> As I understand it, Pontiac did a "hybrid" external/internal balancing. Their engine assembly lines had to balance rotating assembly's together as a set before assembly in the block. While none of this answers your questions, I've always been told that once the rotating assembly is balanced, those parts are "matched" together and changing anything upsets that balance match. You can try other flywheels but it will still be hit or miss. A lot of it might depend on how close the machine shop took their balancing. Some shops provide a closer to "zero" tolerance than others.
> Just my two cents..


And they balanced the pressure plate by itself.


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## Jim K (Nov 17, 2020)

wooftfd said:


> the flywheel was ok until they screwed up the machining on it, now the entire engine is out of balance, and I'm uncertain if I can just replace the flywheel, or is every stock flywheel different weight?


Doing some thinking here, one possible avenue is to take the flywheel, pressure plate and possibly the clutch disc in and have them balanced to a "zero" perspective as a unit.. Given what you are dealing with, it's all going to be PITA, labor intensive work.


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> They said the surface had a couple of hot spots, and wanted to just clean it up, but didnt get it square when they did it, so it was machined off plane. Once they figured that out, they re-squared it up, but had to take off more material to do that. There is a vibration now thats new, without the clutch installed, engine and flywheel only. In order to change the flywheel out, doesn't the entire rotating assembly need to be re-balanced with the new flywheel?
> Yes, had to shorten the driveshaft, and re-used the stock crossmember, jut move it back 1 inch.


Im no expert on balancing... Sounds like @Jim K knows a good deal... but certainly, once your engine was rebuilt, all bets were off. I would get a quality aftermarket flywheel and try that.

I just did a TKX conversion. My original 400 was rebuilt 10k, prior, and was originally an auto. I put a Ram flywheel on.

How do you know you have a vibration? Is that car on the road? Did you check your drive angle?


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## Baaad65 (Aug 29, 2019)

No expert at this for sure but if the motors balanced can't you just buy a neutral or individually balanced flywheel I can't remember what they called it. I had to switch the 10" flywheel that Butler installed to a PRW 11" and a McLeod Super Street Pro clutch, just slapped it together and have no vibration.


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> In order to do that, I'm going to have to re-balance the engine with the new flywheel, right?


No. I just did this entire job.


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## armyadarkness (Dec 7, 2020)

FAQ - Powetrain: TREMEC TKX - Automatic to Manual Conversion


This is my final write up for the swap. It is NOT ANY CHEAPER to do a Muncie than a Tremec.. in fact, it's more expensive. A quality Muncie rebuild is going to cost over $2500 and you wont have overdrive. So, yes, you can buy a used cheap Muncie, but that's on you if you choose to forgo the...




www.gtoforum.com


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## wooftfd (Apr 6, 2021)

Jim K said:


> Doing some thinking here, one possible avenue is to take the flywheel, pressure plate and possibly the clutch disc in and have them balanced to a "zero" perspective as a unit.. Given what you are dealing with, it's all going to be PITA, labor intensive work.


Yea, and without knowing the balance weight of the flywheel that got screwed up, welding on a weight, then running the engine to feel for vibration sounds like a shitty time...
I think I might have to pull the engine, buy a new, externally balanced flywheel, and have it all re-balanced...
And bring the bill to the machine shop... $#%&!!!!!!!


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## Baaad65 (Aug 29, 2019)

....and isn't the clutch assembly balanced by it's self by the manufacturer also?


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> In order to do that, I'm going to have to re-balance the engine with the new flywheel, right?


I ordered a Ram flywheel, took out my TH400, took off the auto flywheel, put the Ram on, bolted up the clutch, bell, trans... and have 3000 miles of 80mph cruising on it, in the last month.


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> the flywheel was ok until they screwed up the machining on it, now the entire engine is out of balance, and I'm uncertain if I can just replace the flywheel, or is every stock flywheel different weight?


Well I've done it more times than I can count, so I sure hope so.

Think about it... Flywheels in manual cars are replaced all day, every day, and no one ever pulls the engine out to rebalance it.


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## wooftfd (Apr 6, 2021)

Baaad65 said:


> ....and isn't the clutch assembly balanced by it's self by the manufacturer also?


They are supposed to be, but not all of them are within spec.


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> My understanding is the shop that did the rebuild (prior to me buying the car) is a serious shop, and builds high end racing engines... The owner assured me it was within a gram or so of neutral
> 
> And they balanced the pressure plate by itself.


I would be throwing away that flywheel and replacing it AND verifying that my driveline angles were right.


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## wooftfd (Apr 6, 2021)

armyadarkness said:


> Well I've done it more times than I can count, so I sure hope so.
> 
> Think about it... Flywheels in manual cars are replaced all day, every day, and no one ever pulls the engine out to rebalance it.


That's kinda where I was going to start, but I dont know enough about the way pontiac cast their flywheels, and how much variation there was from flywheel to flywheel.
If I can just buy a new, externally balanced wheel, if they were pretty much all the same weight, Id be good to go!!!!!
Does anyone know, when the factory balanced the assembly, did they remove, or add weight on the flywheel, or within the crank?


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## armyadarkness (Dec 7, 2020)

Jim K said:


> Doing some thinking here, one possible avenue is to take the flywheel, pressure plate and possibly the clutch disc in and have them balanced to a "zero" perspective as a unit.. Given what you are dealing with, it's all going to be PITA, labor intensive work.


I think we might be partially misunderstanding him here.... a bit of confusion...

Flywheels are replaced all over the world, all day, every day. It's what you do when you replace the clutch. Who is ever pulling the engine apart to rebalance it with a new flywheel?

In my useless half-assed opinion... you provided an accurate assessment of the balancing procedures which the factory used, but they no longer apply to his situation.

Everyone of the 30,000 people on the internet, who have done a TKO/TKX swap, have all replaced the flywheel without taking the engine apart.


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## wooftfd (Apr 6, 2021)

armyadarkness said:


> No. I just did this entire job.


I sure like the sound of that!


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> They are supposed to be, but not all of them are within spec.


There aint much "in spec" on a 55 year old car


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## wooftfd (Apr 6, 2021)

armyadarkness said:


> I think we might be partially misunderstanding him here.... a bit of confusion...
> 
> Flywheels are replaced all over the world, all day, every day. It's what you do when you replace the clutch. Who is ever pulling the engine apart to rebalance it with a new flywheel?
> 
> ...



Thats right, they would need to all be about the same!


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> I sure like the sound of that!


As I mentioned... Think about it... Every GTO and Chevelle owner on the web, who did a Tremec conversion on an auto, received a flywheel in the mail, bolted it on, and drove down the road. I know guys pushing 700HP, who did it.

Just in this forum alone there are hundreds who have done the swap. No one matched the flywheel to the engine, and no one took the engine apart.


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> Thats right, they would need to all be about the same!


There are literally 30,000 people who have replaced an auto with tremec. 

If you look in my thread, youll see part numbers for the Ram flywheel that I used. If you get it, make sure to get the proper bolts, too.


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## wooftfd (Apr 6, 2021)

armyadarkness said:


> Im no expert on balancing... Sounds like @Jim K knows a good deal... but certainly, once your engine was rebuilt, all bets were off. I would get a quality aftermarket flywheel and try that.
> 
> I just did a TKX conversion. My original 400 was rebuilt 10k, prior, and was originally an auto. I put a Ram flywheel on.
> 
> How do you know you have a vibration? Is that car on the road? Did you check your drive angle?


Angle is correct, vibration is there when on the road, and without the clutch installed, around 2kRPM, on a lift. I think they just lightened the flywheel so much it no longer balances the engine, or their milling is still uneven? I think I need to grab a stock, new, externally balanced flywheel, and see what it does!


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## armyadarkness (Dec 7, 2020)




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## armyadarkness (Dec 7, 2020)

That's what I used


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## ponchonlefty (8 mo ago)

i used to work in a small machine shop. i have surfaced flywheels before.we used an arbor that fit the flywheel kinda like the way it does on the crank. if the flywheel ran untrue we could tell. if it had hot spots the surface was like it was hardened in those spots. the tool would push off and not give a flat surface. i think the correct way to surface the flywheel would be blanchard ground. i bought a new ram flywheel and the surface is ground not turned on a lathe. i have a pontiac vibe manual trans. replaced the clutch and pressure plate and its fine. i would replace the flywheel with new. hope this helps.


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## Baaad65 (Aug 29, 2019)

wooftfd said:


> Angle is correct, vibration is there when on the road, and without the clutch installed, around 2kRPM, on a lift. I think they just lightened the flywheel so much it no longer balances the engine, or their milling is still uneven? I think I need to grab a stock, new, externally balanced flywheel, and see what it does!


Right and get your money back for the shit job they did on the flywheel!


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## the65gto (Oct 9, 2008)

Len Williams, Len Williams Auto Machine has a statement on his engine rebuilds. " *Manual transmission will need to send the flywheel for balancing or we can supply you with a new steel wheel.


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## armyadarkness (Dec 7, 2020)

the65gto said:


> Len Williams, Len Williams Auto Machine has a statement on his engine rebuilds. " *Manual transmission will need to send the flywheel for balancing or we can supply you with a new steel wheel.


I'm sure that the pro's will always have stringent, specialty requirements. Kind of like Suave insisting that you lather, rinse, and repeat. In a perfect world, we would all have everything balanced and all be making 1 HP per cubic inch, but the world is filled with Mazdas, Toyotas, and Hondas, with 300k on them, and on their 8th flywheel.


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## 67ventwindow (Mar 3, 2020)

Might be because both are for sale and he doesnt want you ruining one of his engines. See Butlers neutral and external balanced Flywheels



https://butlerperformance.com/c-1234750-engine-components-external-flexplates-flywheels.html




*Manual transmission will need to send the flywheel for balancing or we can supply you with a new steel wheel.


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## armyadarkness (Dec 7, 2020)

67ventwindow said:


> Might be because both are for sale and he doesnt want you ruining one of his engines. See Butlers neutral and external balanced Flywheels
> 
> 
> 
> ...


Definitely a lot of marketing at work here!

Its interesting the top engine builders recommend it, yet neither Silver Sport, Modern Driveline, American Powertrain, or Treme mention it. Marketing indeed.


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## Baaad65 (Aug 29, 2019)

67ventwindow said:


> Might be because both are for sale and he doesnt want you ruining one of his engines. See Butlers neutral and external balanced Flywheels
> 
> 
> 
> ...


That's what their called


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## wooftfd (Apr 6, 2021)

I do have a question on the balancing requirement for a new flywheel, aren't they out of balance from the factory? Part of the external balancing? Do they determine the rotation, and weight location, and just keep it close to those numbers when they re surface?


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## RMTZ67 (Mar 12, 2011)

The machine shop that did my machine work neutral balanced my engine, I then took my original flywheel elsewhere and had it turned and balanced with my ne pressure plate and clutch. It looked like a Franken setup when I got it back. It was marked how to line it all up on install. Here are some picks
No vibrations whatsoever. have you transmission setup zero balanced if you haven't done so, and see what happens.


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## ponchonlefty (8 mo ago)

that would be a question for the flywheel manufacturer.but good question.ram flywheels i think are made the in the us. maybe give them a call.


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## Jim K (Nov 17, 2020)

wooftfd said:


> I do have a question on the balancing requirement for a new flywheel, aren't they out of balance from the factory? Part of the external balancing? Do they determine the rotation, and weight location, and just keep it close to those numbers when they re surface?


I've always had any replacement flywheel balanced checked before i put it on. The one exception to that is when I replaced a factory flywheel with a genuine GM flywheel on a factory stock motor. I know the factory had an "acceptable" range for engine vibration.
One other this.. I gather from reading you know the shop where the motor was rebuilt/balanced. You might consider talking to them about the current situation and see what they recommend.


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## Jim K (Nov 17, 2020)

RMTZ67 said:


> The machine shop that did my machine work neutral balanced my engine, I then took my original flywheel elsewhere and had it turned and balanced with my ne pressure plate and clutch. It looked like a Franken setup when I got it back. It was marked how to line it all up on install. Here are some picks
> No vibrations whatsoever. have you transmission setup zero balanced if you haven't done so, and see what happens.


RMT,
that's what my flywheel, pressure plate looked like after balancing with all the associated marks for alignment.


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## 67ventwindow (Mar 3, 2020)

Pontiac's are generally internally balanced with a neutral flywheel so nothing needs to be done. Do you have documentation that your Pontiac was externally balanced? One off externally balanced engines would require crank and flywheel to be balanced together.


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## armyadarkness (Dec 7, 2020)

67ventwindow said:


> Pontiac's are generally internally balanced with a neutral flywheel so nothing needs to be done.


That sure seems logical... and yes, my Ram flywheel was definitely a high quality part... But on my 70 Vette, I used a $60 Luk from Napa.


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## Jared (Apr 19, 2013)

I'm running a Len Williams bottom end in mine. He told me the flywheel balance was required as part of his build. I'm thinking this is to prevent someone from using an extremely worn or cracked flywheel and then blaming him for a failure. I had him provide a one because mine was heat cracked and a million years old. I'm betting that he balanced the crank and then checked that the fly wheel was zero balanced but I can't say that 100% because I didn't ask. I'm thinking even if there was a slight imbalance that the harmonic damper would absorb it. I'm thinking if the OPs build is just a stock rebuild (or slightly modified) a good quality replacement will solve the issue.


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## lust4speed (Jul 5, 2019)

Couple of important things to set straight. Pontiac externally balanced their engines because it was the most economical thing to do. This external balance never varied, and was a set amount (seems like six inch ounces but can't remember), and every flywheel in the crate waiting for assembly was exactly the same balance. Pontiac could have internally balanced their engines by adding heavy metal, but that is expensive, and it was simple to take some of the offsetting balance and transfer it to the flywheel/flexplate. Crank weights can only be so large before scraping a rod, block, or bottom of the piston. You can take a stock flexplate off any Pontiac V8 and it will bolt up to another and not screw up the balance since they all have exactly the same offset balance. Same with ordering an aftermarket external balance flexplate with just bolting it on.

Then the need for speed arrived and with a much lighter rotating assembly an engine could be internally balanced without the need for the offsetting external weight difference. Sometimes a little Mallory metal was needed to be added for the internal balance, but most of the time cranks actually have additional weight removed with drilled holes in the counterweights. Either internal or external balancing work perfect as long as the guy doing the balancing does his job. What you don't want to do is swap parts. Neutral balanced flywheels have to go on internally balanced engines and stock external balance flywheels need to go on stock balanced engines. Taking cuts off the pressure plate side of the flywheel does nothing to change the balance. You could slice over and over and nothing would change. I have flywheels surfaced all the time and don't bother to check the balance because if it was correct before the cut it will be correct after the cut. Since you now have a vibration, then something else has changed. Same flywheel? Engine side look to be altered recently?

If your engine builder has a record of how he balanced the assembly, it's simply a matter of ordering out a matching flywheel. Most production shops stay with the external balance so it is imperative that you find out. Would you happen to have a photo of the engine side of the flywheel out of the car? Also, the total weight of the flywheel changes nothing. Flywheels can be very light like the aluminum replacements to heavier than original units.


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## ylwgto (Oct 27, 2009)

After reading this whole thread I went back to your original post. If your car had no vibration with the original 3 speed in it, then your machine shop messed with the existing flywheel (and maybe got it wrong) for this conversion and now you have a vibration using the flywheel they machined, then it is the flywheel...they botched the job. 

I'd demand they order you a new flywheel and you'll likely be perfectly fine.


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## PontiacJim (Dec 29, 2012)

wooftfd said:


> I do have a question on the balancing requirement for a new flywheel, aren't they out of balance from the factory? Part of the external balancing? Do they determine the rotation, and weight location, and just keep it close to those numbers when they re surface?


1.Stock engines are externally balanced.

2. Stock flywheels/flexplates are not neutral balanced.

Pontiac uses the flywheel to externally balance the rotating assembly. This is why the flywheel must be fitted in a specific orientation on the crank. The balance process from the factory allows any factory flywheel to be installed as is - no need to re-balance.

3. A neutral balanced flywheel/flexplate on a stock external balanced engine will vibrate.

4. A stock flywheel/flexplate on an internally rebalanced engine will vibrate.

The machine shop should have had no problems simply dressing the surface of the flywheel. The material removed should not have affected the balance - anymore than having any flywheel resurfaced, and I have had a couple resurfaced when installing a new clutch/pressure plate and never an issue. However, if the flywheel were cut at an angle, then you have a "heavy" side and "light" side which would affect balance. But, the shop figured out their goof and cut the flywheel square again.

Assume they have the specs on how much you can surface the flywheel and not bee too thin. The Pontiac flywheel has a slight bevel along the shoulder and I believe as long as you have some bevel, you are OK - but I am not an expert on flywheels.

The previous shop could have included the pressure plate in their balancing of the engine. You stated you only had the flywheel on and when tested by itself you got the engine vibration. Am I reading that correct? So you may have wanted to have your re-surfaced flywheel and new pressure plate re-balanced by supplying both to your machine shop to have them, or another, re-balance the 2 as an assembly. So your vibration may be coming from the flywheel without the balanced pressure plate OR the resurfaced flywheel and an un-balanced pressure plate.

Most all aftermarket steel flywheels are "neutral" balanced - meaning it will have to be balanced using your old/factory flywheel and matching the balance. BUT, if as I stated, the pressure plate was balanced with the flywheel, then the old factory flywheel/balanced pressure plate would have to be matched to a new flywheel/pressure plate. Should not be a big deal to have this done.

Otherwise, yes, you would want to pull the engine, disassemble it, bring all the rotating assembly down to a shop to include rods,piston, pins, rings, bearings, crank, bearings, harmonic dampener, new flywheel - which at that point you might as well rebuild the engine.

Is the machine shop going to pay for this? Nope. Why not? Because even though they did not re-surface the flywheel correctly the first time, they found their error and re-surfaced it flat. Now you might want to verify this with another shop and get their opinion. If they say it is good, then it should not be the flywheel that is causing the vibration. BUT, it could be that it is the unbalance of the flywheel BECAUSE it was balanced as a unit along with the pressure plate.

So the wild card here may be the pressure plate.

So I would NOT pull the engine until you have exhausted your options with the flywheel/pressure plate. IF the first shop is at fault as verified/confirmed by another competent machine shop, then about the best you will do is to have the first shop refund you the money they charged to have the flywheel resurfaced originally.

And that is my opinion on it all.


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## armyadarkness (Dec 7, 2020)

lust4speed said:


> If your engine builder has a record of how he balanced the assembly, it's simply a matter of ordering out a matching flywheel.


It sounded as though the engine builder was the one milling the flywheel... I was a tad confused.


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## armyadarkness (Dec 7, 2020)

So... 

During three years of thorough, intense, daily Tremec-swap research, spent on the Corvette forum and here, talking personally to the owners of Hanlon, Silver Sport, MDL, and American Powertrain, watching all of the video's, and arguing "bell housing alignment" until the cows came home... How is it that never once, anywhere, was flywheel balancing mentioned?

Everyone unanimously demands that bell alignment be done, but this seems far more critical.

Am I missing something? Is this one of those things like; you're not supposed to get out of you car, smoke, or talk on the phone while refueling, but everyone does it? Or like you're not supposed to plug more than two things into an outlet?


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## geeteeohguy (Feb 2, 2008)

Flywheels aren't turned....or aren't supposed to be. They are Blanchard ground on a grinding machine. The machine shop is responsible for damaging your flywheel. The problem happened after that. The machine shop needs to buy you a new flywheel, and you need to install it on the engine and verify runout after it is installed with a dial indicator.


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## the65gto (Oct 9, 2008)

Many years ago, I had my block bored .60 over by a machine shop. That shop also balanced and "blueprinted" and assembled the short block. One detail I remember is him showing me the alignment marks on the end of the crank and the flywheel that he put there. As far as Len Williams, my thoughts only, is that he does not require a trade in block and most likely people who shipped their used flywheel to him was a piece of crap that needed work??. Don't know what he charges for a new flywheel, but the cost of shipping an old flywheel to him along with possible charges to make sure it is acceptable would probably make getting a new one from him a $$ judgement call?. I would feel better if everything he gave me back was all his work and parts.


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## geeteeohguy (Feb 2, 2008)

I agree on the shipping, etc. Not worth it and jumping over a dime to pick up a penny. The fact that Len is even willing to take your old junk and try to work with it if you are on a budget speaks volumes on his old-school work ethic, IMO. Those types of guys are disappearing these days. If it were me, I'd have him do the whole thing too, on his timeframe.


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## Lovetoweld (Nov 26, 2013)

wooftfd said:


> Changing out the original 3 speed manual for a Tremick TKX in my 64, stock (rebuilt 10K ago 389), externally balanced...
> The machine shop chucked up my flywheel crooked, 9/1000 out of plane, to fix what they did, had to take about 11/1000 off.
> Now theres a vibration at 2000RPM... Any ideas on how to fix this? Should I just take the motor out, re-balance it?
> Did Pontiac balance every engine on the line? Did they have a stack of flywheels, different weights, and grab whatever the particular engine needed to make its specific balance?
> I have another used flywheel, might it be closer in balance then what I have now?


If I were you I would contact Butler Performance The experts on Pontiac Engines
(866)762-7527


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## wooftfd (Apr 6, 2021)

lust4speed said:


> Couple of important things to set straight. Pontiac externally balanced their engines because it was the most economical thing to do. This external balance never varied, and was a set amount (seems like six inch ounces but can't remember), and every flywheel in the crate waiting for assembly was exactly the same balance. Pontiac could have internally balanced their engines by adding heavy metal, but that is expensive, and it was simple to take some of the offsetting balance and transfer it to the flywheel/flexplate. Crank weights can only be so large before scraping a rod, block, or bottom of the piston. You can take a stock flexplate off any Pontiac V8 and it will bolt up to another and not screw up the balance since they all have exactly the same offset balance. Same with ordering an aftermarket external balance flexplate with just bolting it on.
> 
> Then the need for speed arrived and with a much lighter rotating assembly an engine could be internally balanced without the need for the offsetting external weight difference. Sometimes a little Mallory metal was needed to be added for the internal balance, but most of the time cranks actually have additional weight removed with drilled holes in the counterweights. Either internal or external balancing work perfect as long as the guy doing the balancing does his job. What you don't want to do is swap parts. Neutral balanced flywheels have to go on internally balanced engines and stock external balance flywheels need to go on stock balanced engines. Taking cuts off the pressure plate side of the flywheel does nothing to change the balance. You could slice over and over and nothing would change. I have flywheels surfaced all the time and don't bother to check the balance because if it was correct before the cut it will be correct after the cut. Since you now have a vibration, then something else has changed. Same flywheel? Engine side look to be altered recently?
> 
> If your engine builder has a record of how he balanced the assembly, it's simply a matter of ordering out a matching flywheel. Most production shops stay with the external balance so it is imperative that you find out. Would you happen to have a photo of the engine side of the flywheel out of the car? Also, the total weight of the flywheel changes nothing. Flywheels can be very light like the aluminum replacements to heavier than original units.


Hes digging up the records for me, engine was assembled 10 years ago... The only thing that was changed was the flywheel, and they did admit to cutting it crocked...


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## wooftfd (Apr 6, 2021)

PontiacJim said:


> 1.Stock engines are externally balanced.
> 
> 2. Stock flywheels/flexplates are not neutral balanced.
> 
> ...


thanks for the great info... I verified that the builder balanced the assembly without the pressure plate... He said his standard was to do the engines alone, then the clutch and trani separate, allows for easire replacement of parts down the road... I brought the shop a different, used flywheel, if that doesn't work, were going to order a replacement from Butler...


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## Jared (Apr 19, 2013)

the65gto said:


> Many years ago, I had my block bored .60 over by a machine shop. That shop also balanced and "blueprinted" and assembled the short block. One detail I remember is him showing me the alignment marks on the end of the crank and the flywheel that he put there. As far as Len Williams, my thoughts only, is that he does not require a trade in block and most likely people who shipped their used flywheel to him was a piece of crap that needed work??. Don't know what he charges for a new flywheel, but the cost of shipping an old flywheel to him along with possible charges to make sure it is acceptable would probably make getting a new one from him a $$ judgement call?. I would feel better if everything he gave me back was all his work and parts.


Len didn't make a huge profit on the flywheel. Price he quoted was low enough where it wasn't worth my effort to order one and have it shipped to him. I have so much into that build that I don't recall what the actual price was, but it was reasonable. He marked both the flywheel and the crank for installation alignment.


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## Jared (Apr 19, 2013)

wooftfd said:


> thanks for the great info... I verified that the builder balanced the assembly without the pressure plate... He said his standard was to do the engines alone, then the clutch and trani separate, allows for easire replacement of parts down the road... I brought the shop a different, used flywheel, if that doesn't work, were going to order a replacement from Butler...


You're handling of this situation backs up my thoughts on how to deal with most people. A calm approach often gets better results than one that is overly emotional. As soon as someone gets mad or upset, communication breaks down and the situation gets worse for all involved. Sounds like your shop knows they made a mistake and is trying to fix it. These things happen and it probably doesn't reflect their typical work, just a bad day for them. Only thing you are out here is the extra time. Let's face it, most of our cars spend way more time up on stands than getting driven anyway. It's part of the fun.

Good luck!


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## armyadarkness (Dec 7, 2020)

I'm still completely stupified as to why *Ive never read about this issue, in any internet forum thread on Tremec swaps.*

Is it because Pontiac flywheels only go on one way, and Silversport is selling everyone neutral balanced flywheels, based on the assumption that their engine is already balanced?

I can appreciate everyones expertise here, but since this thread started, I've been questioning this MASSIVE loop hole, and so far there has not been a single explanation. 

So am I to assume that everyone who did a Tremec swap on an auto, pulled their engine, took it apart, and re balanced it with the new flywheel!!!!!!!!!?????


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## Jared (Apr 19, 2013)

I agree. I always thought the neutral flywheel meant that you could install it in any location. There is no guide pin and the bolt pattern will line up in any position. I have a Mustang with a 302 that is an externally balanced engine. The 351 was the same way but had a different off balance. You can only bolt the flywheel on in one position, it's the only way the bolt holes line up and you need the correct counter balance because they are different. When I talked to Darrin at Nitemare early in my build (a couple years ago) all he said was neutral flywheel and nothing about having to orient it a certain way on the crank. He seemed confused that my builder (Len) needed the flywheel at all. If the flywheel can only go on one way, Amy had a 1 in 6 chance of getting it right, so either he's really lucky (87.5% chance of getting it wrong) or it really doesn't matter. I'm going with the later since a bunch of guys do these swaps and someone would be getting it wrong.


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## Jared (Apr 19, 2013)

https://butlerperformance.com/n-13498-internal-neutral-vs-external-stock-balance.html



Interesting. What do you do if you have a stock engine and need to replace the flex plate or flywheel?


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## michaelfind (Dec 14, 2018)

I have respect for both Butler and Len Williams to do the right thing.


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## wooftfd (Apr 6, 2021)

my understanding is that the flywheel only bolts on in one orientation


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> my understanding is that the flywheel only bolts on in one orientation


So again, if your engine is balanced, and the flywheel can only go on one way, and it's balanced, too, then what are we all talking about?

I know Im no expert on this, but the math is not adding up.


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## armyadarkness (Dec 7, 2020)

Going back to your first post, you do mention that your engine is EXTERNALLY balanced... so from what Im gathering, Pontiac used the flywheel for externally balancing... However, it also seems that the expert opinion of the pro's on here, is that they used the same weight on every single flywheel... So...

If that is in fact your situation, EXTERNALLY BALANCED"you would merely need a new, OEM flywheel, and you'd be done.


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## armyadarkness (Dec 7, 2020)

lust4speed said:


> This external balance never varied, and was a set amount (seems like six inch ounces but can't remember), and every flywheel in the crate waiting for assembly was exactly the same balance.


Having now read through all of these posts, and understanding it all better... your statement here seems to answer the question quite well. 

If his engine is externally balanced, then he merely would need an OEM flywheel.
If his engine is internally balanced, then he can use any neutral balanced flywheel.


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## armyadarkness (Dec 7, 2020)

wooftfd said:


> I verified that the builder balanced the assembly without the pressure plate...


So, are you saying that it was internally balanced? That's how that sounds, and if so, you just need a neutral flywheel.

A builder could not have balanced and externally balanced assembly, unless he had all the parts.


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## Jared (Apr 19, 2013)

OK. I did a little more digging. Looks like the stock Pontiac engines were externally balanced but were all balanced the same (like the Ford), most engines, when rebuilt, are balanced internally. You need to select the correct flywheel which is probably why rebuilders want to "balance" the wheel you are going to use. This makes sure you don't run an externally balanced wheel on an internally balanced engine. Based on what I could find, they only bolt on in one orientation so I was wrong on that front. The bolt pattern must be very close to even because they looked evenly spaced to me. I had the mark on the wheel and the crank so I didn't run into it not fitting and having to find the correct spot. The Ford fly wheel is obviously not drilled even which is where my confusion came from. This all being said neutral balanced and external balanced are not the same thing. You really need to know how your engine was balanced to select the correct wheel.

Learn a new thing every day. Sorry if I contributed to any confusion.


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## Baaad65 (Aug 29, 2019)

armyadarkness said:


> So, are you saying that it was internally balanced? That's how that sounds, and if so, you just need a neutral flywheel.
> 
> A builder could not have balanced and externally balanced assembly, unless he had all the parts.


Do you have any vibrations at all at any speed, if not you should be ok unless the balancer is taking it up but isn't that what's it's for? There was a Pontiac engine video posted here or your other residence that showed how they balanced the motor but I can't remember if it was internal or external now.


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> Do you have any vibrations at all at any speed, if not you should be ok unless the balancer is taking it up but isn't that what's it's for? There was a Pontiac engine video posted here or your other residence that showed how they balanced the motor but I can't remember if it was internal or external now.


lol... Don't bring me into it!! Im just trying to make sense of it.


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## armyadarkness (Dec 7, 2020)

Jared said:


> Based on what I could find, they only bolt on in one orientation so I was wrong on that front.


No big deal... I found a lot of it hard to follow, but like you, I learned a LOT here.

The only thing left for me to understand, is why the OP still seems to be going down the machine shop balancing route.


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## Baaad65 (Aug 29, 2019)

armyadarkness said:


> lol... Don't bring me into it!! Im just trying to make sense of it.


You're the one who said you maybe missed something and was worried, I was just asking a question.


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## RMTZ67 (Mar 12, 2011)

Would I be correct in saying, if you put a new neutral balanced flywheel and nothing else and had the vibration still, then it would be the engine? He'll I am confused as well. I swapped anything I could find in the junk yards back in the days and don't remember having vibration issues. Or maybe I was taking something that helped with that lol.


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## wooftfd (Apr 6, 2021)

Ok, so the engine was built to externally balanced factory specs, which means it has a stock, slightly out of balance factory flywheel on it. The engine was balanced during the rebuild with the flywheel, and dampner installed. The builder then balanced the clutch assembly because he has found aftermarket clutches to sometimes be out of spec. Fast forward to now, when the shop sent out the original flywheel to be surfaced, the machine shop really butchered it, requiring a large amount of material to need to be removed to get it back to plane. With the original flywheel reinstalled, no clutch, there was a new vibration in the motor. I myself was unsure of the factory process Pontiac used to balance the motors, and the tolerances that the factory flywheels came out, and feared that I would be forced to remove the motor, buy a new flywheel, and re-balance it all over.... But the members here filled in my understanding, and it makes perfect sense that flywheels are replaced all the time, and as long as you stick with your engines balance situation (external or internal) Any in spec flywheel should work.


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## PontiacJim (Dec 29, 2012)

wooftfd said:


> Ok, so the engine was built to externally balanced factory specs, which means it has a stock, slightly out of balance factory flywheel on it. The engine was balanced during the rebuild with the flywheel, and dampner installed. The builder then balanced the clutch assembly because he has found aftermarket clutches to sometimes be out of spec. Fast forward to now, when the shop sent out the original flywheel to be surfaced, the machine shop really butchered it, requiring a large amount of material to need to be removed to get it back to plane. With the original flywheel reinstalled, no clutch, there was a new vibration in the motor. I myself was unsure of the factory process Pontiac used to balance the motors, and the tolerances that the factory flywheels came out, and feared that I would be forced to remove the motor, buy a new flywheel, and re-balance it all over.... But the members here filled in my understanding, and it makes perfect sense that flywheels are replaced all the time, and as long as you stick with your engines balance situation (external or internal) Any in spec flywheel should work.


Yes. OK, one more time.

So you will read that the Pontiac engine is both internally balanced and externally balanced - both being somewhat accurate and inaccurate at the same time. WTF you say?

Externally balanced means that the front harmonic balancer, the flywheel/flexplate, or a combination of both are used to balance the rotating assembly.

Internally balanced, or "neutral" balancing, means the crank/rods/pistons/pins/rings/bearings are all balanced as an assembly WITHOUT the harmonic balancer/flywheel/flexplate.

Looking at the Pontiac, let's start with the *Harmonic Balancer.*

The harmonic balancer on a Pontiac is "neutral balanced", ie not counter drilled or weights added to create an offset balance. If you spin it, it will spin with no vibrations as it is fully balanced.

As an example, Pic 01 is a Mopar 360 harmonic balancer where you can clearly see the milled area on the balancer. This means the balancer is weighted in a manner to be externally balanced to meet the demands of the rotating assembly to bring it into balance. If you were to spin this balancer by itself, it would have a nasty vibration due to its counter-balance properties. If I put an aftermarket "neutral" balancer on my stock 360, it would vibrate like hell, so the stock engine needs the offset balanced balancer.

So, what is odd with the Pontiac is that the rotating assembly is sorta looked at as 2 halves - the front half and the rear half. The front half of the rotating assembly is balanced, this uses the "neutral" balanced harmonic balancer - which is technically referred to as a dampener, not a balancer.

It is the back half of the crank that is slightly out of balance. 

The factory Pontiac flywheel/flex plate has a built in unbalance to counteract the slight inbalance of the factory rotating assembly. The crank is indeed balanced using the average weights of the rods/pistons/pins/rings in the same manner your machine shop would balance a crankshaft and using a more accurate weight of all your parts and then they use what are called "bob weights" that go onto the crank's rod throws that are the same weights of the parts being used. The the crank is spun up and the machine indicates where on the crank either weight must be added to the crank's counter weights or weight removed.

Pontiac flywheels/flex plates are made with a 6-inch ounce unbalance to compensate for an internal unbalance - which I have read is due in part to the rear counter weight, with heavy pistons and cast rods you need more counterweight and with limited room for counterweight they had to also use an external weight. So all Pontiac engines were balanced with this in mind and all used the same unbalanced flywheel/flex plate.

The crank flange is drilled offset so that the flywheel/flex plate can only be mounted one way. By doing this, you can install any Pontiac flywheel/flex plate from any other Pontiac and not create an unbalanced engine.

*Neutral Balance*, or* Internal Balance* is when the crank and related parts are balanced WITHOUT the harmonic balancer and flywheel/flex plate. This can cost more money when additional weight is needed to be added to the counterweights using a heavy metal called mallory. Using the harmonic dampener and flywheel/flex plate as part of the balance can save money if mallory metal has to be used. By neutral/internal balancing an engine, it can be of advantage when swapping flywheels - you don't have to use a balanced flywheel that matches your rotating assembly balance, you can use a "neutral balanced" flywheel just like the "neutral balanced" Pontiac harmonic dampener. So if you wanted to experiment with a 30 lb flywheel versus the 40 lb flywheel, or an aluminum flywheel, you would not have to have each one balanced to the rotating assembly, you would just pull it out of the box and bolt it on because your engine's rotating assembly was "neutral/internally" balanced and your flywheel selection was "neutral" balanced.

So why can you buy an aftermarket flywheel and slap it on without any vibrations? Many are already weighted for a Pontiac engine since Pontiac factory flywheels/flex plates all have the same unbalance. Some will state "neutral balance" but may refer to the term "neutral balanced" often associated with the Pontiac engine when in fact the flywheel is slightly unbalanced to create a "neutral balanced" engine. So you might want to inquire as to what "neutral" means according to the brand you are selecting and what they call "neutral balance."

Generally, any engine you build will be using all new parts and will either be built with a balanced kit or you will have your machine shop balance the assembly.


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> You're the one who said you maybe missed something and was worried, I was just asking a question.


Im just saying, this post has nothing to do with me or my car, nor do I want it to! Im just trying to clarify stuff for my own knowledge and my manual swap thread updates!


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## armyadarkness (Dec 7, 2020)

RMTZ67 said:


> I swapped anything I could find in the junk yards back in the days and don't remember having vibration issues.


And there you have it.


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## the65gto (Oct 9, 2008)

When I had my engine balanced, the builder gave me a pretty long data sheet that showed all the components weights. Some parts were new and some were original. I seem to remember, that all i.e. pistons were matched to the lightest one. Same with rods etc. This a rebuild situation, not directly from the factory situation. The whole rotating assembly, may or may not have included the harmonic balancer,? For this reason, the flywheel/crank was marked so as to keep the flywheel in the same location as it was when balanced. Now, yes the flywheel can be mounted on the crank using any bolt pattern but only one with the balanced orientation. How much of this really makes a difference I am not sure. If at some time that the flywheel was replaced you might loose the balance? Does it matter or not, probably not for street drivers like me. At some point many years later, I did replace the clutch/pressure plate and had the fly wheel resurfaced. Escapes me now if I followed the balanced orientation when I put it back together. A year or so later, running normal etc, went on a grocery run at normal speeds when all hell broke loose. When I took out the engine and opened it up, the crank was in 2 pieces and destroyed the engine. Related to balancing or just plain bad luck? This was about 30 years ago and I am still not over it.


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## wooftfd (Apr 6, 2021)

my experience so far, if you installed it out of balance, you would have felt it right away...


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## Jared (Apr 19, 2013)

the65gto said:


> When I had my engine balanced, the builder gave me a pretty long data sheet that showed all the components weights. Some parts were new and some were original. I seem to remember, that all i.e. pistons were matched to the lightest one. Same with rods etc. This a rebuild situation, not directly from the factory situation. The whole rotating assembly, may or may not have included the harmonic balancer,? For this reason, the flywheel/crank was marked so as to keep the flywheel in the same location as it was when balanced. Now, yes the flywheel can be mounted on the crank using any bolt pattern but only one with the balanced orientation. How much of this really makes a difference I am not sure. If at some time that the flywheel was replaced you might loose the balance? Does it matter or not, probably not for street drivers like me. At some point many years later, I did replace the clutch/pressure plate and had the fly wheel resurfaced. Escapes me now if I followed the balanced orientation when I put it back together. A year or so later, running normal etc, went on a grocery run at normal speeds when all hell broke loose. When I took out the engine and opened it up, the crank was in 2 pieces and destroyed the engine. Related to balancing or just plain bad luck? This was about 30 years ago and I am still not over it.


Just 2 pieces? Mine broke into 5 but I think it was due to a failed oil pump.


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## the65gto (Oct 9, 2008)

That's the question that I cannot answer. How close does a person who balances engines work towards when they call it good. An online video, said < 30 grams is ok, but this operator worked on it until he got it down to 3 grams. It was a Chrysler, don't know if Pontiac, Chevy etc. has the same tolerance. Interesting reading here" Balancing an engine - PONTIAC ZONE TECH FORUMS" and read post #7 :O)


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## geeteeohguy (Feb 2, 2008)

I've installed tons of flywheels and clutches and flex plates over the years on in-service vehicles with nary a vibration problem.


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## Machinest-guy (Jul 19, 2019)

I'd like to offer a few observations about engine balance and resurfacing flywheels. 

Years ago when I was working in an automotive machine shop we resurfaced dozens of flywheels per week sent in from many of the repair shops in town. Most of running our flywheel grinder fell to me as "the new" employee. I can say with certainty very few flywheels were the same insofar as how much work they needed to return to service because ring gears, inset friction surfaces, countersunk pressure plates, dowel pins, and so on all needed consideration job to job to job. But balance was rarely an issue, and never an issue on Pontiac flywheels, because metal is removed equally all around the opposite side from the mounting flange. Generally speaking if a Pontiac flywheel was burnt with hard spots we would remove the grinding cup wheel from our Van Norman grinder ( a machine similar to a Blanchard Grinder used widely in industrial machine shops) and replace it with a cutting tool. We'd lathe cut the flywheel so hard spots would start to protrude and cracks would be gouged out. If the hard spots didn't get too large and the cracks didn't run too deep we'd then remove the cutting tool and replace the grinding cup stone to grind the flywheel flat and true to the mounting flange. Limits for stock removal with the cutting tool were .010 - .015 per pass. Limits for hard spot protrusion were in the .030 to .050 range. If we needed to take more than .050 - .100 off a flywheel we'd try to sell the customer a new flywheel or send them to the dealer. Thin flywheels or reduction of the flange dimension can cause clutch linkage geometry issues.

The advantage of lathe cutting was time saved. Our grinding cup wheel was limited to about .003 per pass and .000 kiss up for a final pass done in the reverse direction to get a more aggressive friction pattern for a new (organic) clutch disc to bed in against. Stellite and ceramic puck clutches came into use much later on and need different flywheel treatment. The lathe tool could take off in one pass what a cup wheel needed 3-4 passes to do. 

Flywheel lathe cutting can go wrong in several ways. The cutter tends to "dig in" because the flywheel might move in the chuck. The flywheel might be bent and overload the cutter causing it to 'dig in". The cutter may go dull mid cut and "dig in". The flywheel flange may not be true to start with or damaged causing excessive run out which the lathe tool "follows" instead of cutting out. Lathe cutting flywheels, in my opinion, should always be followed by grinding. Flywheel grinding should always be followed by flipping the flywheel over in the chuck, measuring with a dial indicator total face run out vs run out of the mounting flange and, if needed; correcting the mounting flange to match the face so both surfaces are parallel to each other. 

None of this work effects a balance change on any Pontiac (and most GM flywheels) I've seen. But if the flywheel is cut or ground out of parallel wobble can make big time problems leading to major failure. Run out or wobble is often mistaken for a balance issue. It feels the same from the drivers seat. A customer might assume because the flywheel is resurfaced it will run true and put it into service without checking for excessive run out. When you don't check you don't find the real problem and assume because metal was "removed" it changed the balance. This is a false assumption based on incorrect machining and assembly procedures. And I should mention there is one case where incorrectly done metal removal from a flywheel can change it's behavior. 

Assume a good but worn flywheel is chucked into a grinder for resurfacing. Assume the hard spots and minor cracks lead to lathe cutting its face. Assume the lathe cutter digs in for some reason - maybe the flywheel is "harder" on one side than the other because of casting chilling when poured. Anyway; the flywheel gets cut out of true to the mounting flange and finish ground. When the machinist checks his work and finds the flywheel face is not true to the flange he cuts the flange to become true..A fix that works well if the lathe cutting goes well, but only if the lathe cutting didn't remove unequal amounts of material...What the job looks like is: the flywheel faces are parallel, the surface finish is good, but the mass of the flywheel is no longer equal around the crankshaft center line. A dynamic imbalance has been introduced to the rotating assembly. You might find the imbalance if you measured the flywheel thickness at a dozen or so spots around the circumference, or maybe not. But the customer will notice it when running.

On balance. 

I've had a hundred or more engine rotating assemblies balanced - more than I can remember in the last 50 years. Each one had different characteristics to account for because when an engine is overhauled it seldom is reassembled with the same weight parts. My understanding from GM school is GM would factory balance their parts to +/- 4 grams. So a reciprocating assembly with a piston, pin, rod, and crank throw counterweight could be high at 16 grams heavy or 16 grams low. Factory replacement pistons were lightened so oversize pistons matched STD bore pistons allowing OEM warranty repairs to be done or overhaul at the dealer level without changing an engines balance factor. Ford Industrial engine school taught the same standard up until about 2000. After that I don't know what they did. Aftermarket balancing is generally done to +/- one gram. To balance parts closer than one gram is possible but you need laboratory environmental controls around your scale. A light puff of breath will change the scale by +/- 2 grams. And the parts need to be dry. No oil or solvent on them. 

The AERA (Automotive Engine Rebuilders Association) recommends to shops all rebuilt engines should be re-balanced. This recommendation results from several factors and came into publication around 2000. 
1) Old pistons are usually tossed out. New aftermarket pistons are generally lighter and nearly certain to be more than four grams different than the factory limit hence will never match the crank throws balance factor. And forged pistons might be chosen which are generally heaver so you need to know what came off the crank to be certain about anything.
2) connecting rods generally become mixed up when done in batches of hundreds at a time. There is no process to assure that the rods reused match the crank they came from. 
3) Flywheel and flex plate and damper changes are far more likely to happen than not so those components, when using them as part of a balanced assembly, will usually never meet a factory OEM new specification.
4) Lighter parts will reduce NVH (noise, vibration, harshness) issues so an engine may have an "unnoticed issue". 

Will this cause a problem ? Maybe and maybe not, but it leads to a disassembly practice including cleaning and weighting any removed part that is a component of a rotating or reciprocating assembly. Then you'll be able to calculate the original engine balance factor, compare that to the new parts balance factor and make an informed decision about re-balancing work if the difference is more than 16 grams, or more than what you'd like for your intended use.

There has been some really good and hard to find information published here. PJ and others have Pontiac's special balancing issues explained well. ( i/e being internally balanced at the front of the crank and externally balanced at the rear) I'd just add that you can static balance a crank or damper or flywheel. It will rotate freely between centers and stop at random points if spun lightly. But the overall mass of static balanced parts when assembled can cause dynamic imbalance. The job of balancing an engine really starts after reciprocating parts are match weighted and after the flywheel and damper are chosen. Dynamic balance work attempts to mitigate forces which are RPM sensitive. Mitigation of dynamic imbalance doesn't fix harmonic resonance which is the dampers job and a completely different force.

V series engines have different balance factors depending on the firing order and what the bank angle is. This leads to balancing to a percentage of the rotating weight. This leads to the fact that a V series engine is only in balance at a specific RPM. Lighter parts raise this RPM point. This leads to two expressions. Over balance, when the engine crank is "heavy" compared to the theoretical bob weight value, and "under balanced" being the opposite condition. Over balance is good for high RPM use as it tends to be easy on the crank because reciprocating weight forces go up as speed rises. Under balance is good for lower speed engines and allows weight removal from the crank increasing RPM acceleration. 

If one looks at a Pontiac crank static and dynamic loads are spread across main bearings in the center 3 webs. The outer main bearings are cantilevered insofar as load support for the damper / pulleys and flywheel go. And you can see the center of mass is not the geometric center of the crank. The back half of the crank assembly is heaver than the front. This introduces a force called "rocking coupling" which the crank must absorb. Forces introduced into the block from the rotating assembly are diminished by using lighter parts. 

A clutch disc never stops or locks up in the same place in relation to the flywheel so needs to be balanced to zero. Generally this is done at the manufacturing level because welding weight on the disc is iffy and can ruin it. A clutch pressure plate is indexed to the flywheel and needs to be assembled the same way it came off. Sometimes they are dowel pinned or index stamped to assure that can happen. The balance procedure is to balance everything else first. The last part of a balance job is the clutch pressure plate which is spun up with the remainder of the rotating assembly. It changes balance of the overall rotating assembly but corrective weight is only added to the cover - usually by welding - which brings the assembly back into balance. I don't think much of balancing a flywheel to a fixture to get to zero. It sorta works but isn't the same thing as using the real parts because of rocking coupling moving the balance point of the real parts which isn't seen when using a fixture.

My nearly new OEM Pontiac iron flywheel weighs 31 lbs and needed about 21 grams to zero balance at 6 inches from crankshaft center line when I checked it last week. Clearly this Pontiac flywheel is not set up to be run internally balanced. Yet it was purchased new from the dealer and installed as received. I didn't notice any vibrations but the car is harsh and aggressive so I could have missed something going on that way. Now the engine is apart because my crank is cracked in four rod journals. I never heard it ping or detonate, but it has been run hard for several thousand miles. So I want to go back together with lightweight parts to minimize dynamic loads which a stroked crank will introduce to the main bearing webs. I'm thinking of why my crankshaft cracked. No answers yet; but I'll prevent all the usual reasons in this build up.

There is some advertising confusion in my mind about the American Powertrain aluminum lightweight flywheels offered by Butler. When I called American Powertrain they said the Internal Balanced APO-FWPO-20001 flywheel had no weight added to it. However Butler advertises two flywheels with the same part number save for an "N" suffix for neutral balance done in their shop to an internal balanced flywheel for $50. I assumed the "stock balanced" flywheel would have weight added to it and should match a SCAT crankshaft they advertise as "Stock Internally" balanced. This came from Greg at Butler. So I ordered a Stock (Internally balanced) flywheel to match a new SCAT crank. It came with a heavy metal balance weight of about 7 grams at 6 inches off crankshaft center line. This is a pretty big difference from the OEM flywheel. And it would seem the work Butler does to create an internal balance flywheel may be simply to knock the balance weight out. The balance weight from American Powertrain was 180 degrees opposite the weight I added to get to zero. 

Then when I talked to Tom at SCAT he said the Pontiac engine was internally balanced and needed a zero weight flywheel. When I mentioned stock is something other than zero he said it didn't matter because the weight was a very small percentage of the spinning load. We agreed I could send my parts to SCAT and they would balance the entire rotating assembly as part of buying their crank. Fair deal. So next week I'm driving to LA to stand next to their balance machine and see what happens when these parts are spun up. I tried to buy a Hays flywheel but HOLLEY bought Hays then discontinued Pontiac flywheels. According to their tech department they have no intentions of bringing Pontiac aluminum flywheels back to market.

I think for all these reasons many owners have mentioned here, each Pontiac engine needs to be considered as a puzzle until every part is examined for engineering compatibility. 

Good luck to us all. Ladd


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