# 1966 Flywheel Bolt size



## 19gto66 (Oct 14, 2019)

Hi All, I am new here and glad there is a source for this question. 

I am converting my 66 to a manual and also just had the 389 rebuilt. I picked up an original 66 flywheel (I hope) but no bolts came with. I purchase some on-line and when they came in they were too long (1")

So my question is what are the correct specs on a 1966 flywheel bolt as far a size. Any original photos? Do they have a shoulder or not. ? Seems like they should. I am guessing the bolt should be 1/2-20 and approx .75" long with a shoulder to make sure the flywheel locks into place.

Also, I gave the engine shop the flywheel figuring they would make sure all was in balance. They said I was all set just need flywheel bolts. I am guess they did not balance flywheel with engine since how could they without the bolts. I read the engine is internally balanced and that the flywheel is zero balanced. So hopefully that's correct. Just need a way to bolt flywheel on correct and secure.

Any help would be great along with photos and a source.
Thanks


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## GTOJUNIOR (Aug 7, 2011)

Jegs and/or Summit both carry ARP Flywheel bolts for the '66.

Disregard the red dots on attached chart that is my app.
Cheers


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## 19gto66 (Oct 14, 2019)

The bolts I have been finding at summit, jegs, etc all have been 1" long or no shoulder. That's why I was hoping someone would post a photo of an original 1966 Flywheel bolt for manual. Based on my measurements the bolts I need should only be 3/4" long and have a shoulder. Do you have part numbers. Also, my flywheel seems to be cast and on back has a number 8621677 Preceding the number is an F 2 overlapping diamonds and then a 6...then the number I listed above.


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## GTOJUNIOR (Aug 7, 2011)

The page above is from the parts book and show length as 7/8 for the V8
MR. Gasket also has a bolt that is very close to OE size.

FWIW the OE bolts on my OHC are very similar and shown below.


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## PontiacJim (Dec 29, 2012)

GTOJUNIOR said:


> The page above is from the parts book and show length as 7/8 for the V8
> MR. Gasket also has a bolt that is very close to OE size.
> 
> FWIW the OE bolts on my OHC are very similar and shown below.



Looks right to me as well. I don't think the shoulder is that important, although I see the aftermarket bolts have them - if you do get a shoulder bolt, make sure the shoulder is not too long and won't allow the bolt to completely seat and hold the flywheel tight to the crank hub. The flywheel fits on the machined shoulder on the crank and this is what aligns and holds it steady.

I used the aftermarket Hays steel flywheel (factory is cast iron) and purchased aftermarket flywheel bolts. There are 2 different thicknesses on the bolt head. The ones I purchased were too thick and the springs in the clutch disc hit them - but learned this later when I removed the engine/trans. So I believe the thinner head bolt is for manual flywheels and the thicker w/washers is for the automatic flex plate. So I suggest whatever flywheel bolt you select to lay the clutch disc on top of the bolts and rotate the disc by hand to ensure that you don't have the same results.

If you want to ensure you have the correct bolts, by them from a Pontiac engine builder/parts supplier. Check out these bolts from Spotts Performance, Part #FWB01 and read the description. Click on here: ENGINE FASTENERS


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## RMTZ67 (Mar 12, 2011)

19gto66 said:


> Hi All, I am new here and glad there is a source for this question.
> 
> I am converting my 66 to a manual and also just had the 389 rebuilt. I picked up an original 66 flywheel (I hope) but no bolts came with. I purchase some on-line and when they came in they were too long (1")
> 
> ...


 Instead of purchasing a new flywheel I had my original one turned and zero balanced along with my clutch. Here are some pics of what was done to it.:surprise: you can see how much was added to the clutch. I was hesitant on installing it, but went ahead and did. No vibrations on the street and at wot. Have not took it on the freeway/ highway yet. I thought my flywheel was zero balanced


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## PontiacJim (Dec 29, 2012)

RMTZ67 said:


> Instead of purchasing a new flywheel I had my original one turned and zero balanced along with my clutch. Here are some pics of what was done to it.:surprise: you can see how much was added to the clutch. I was hesitant on installing it, but went ahead and did. No vibrations on the street and at wot. Have not took it on the freeway/ highway yet. I thought my flywheel was zero balanced



The flywheel is said to be zero balanced, but if you had the pressure plate & flywheel balanced together, that may be where the adjustments comes in. I have had previous set-ups that were balanced and have found a small bolt welded to the pressure plate used in balancing. Suppose each shop has their way of doing things.

And even though the flywheel may be zero balanced, what the factory calls zero balance as opposed to a shop that can pull it in even tighter balance, is probably different.

I had my Hays flywheel balanced to the rotating assembly by supplying all the aftermarket parts such as the crank, rods, pistons, rings, balancer, etc. and my flywheel which is zero balanced had several small drill marks in it to remove some metal to fine tune that "zero balance" steel flywheel. So in this instance, the individual parts were first equalized in weights, then balanced as an assembly and using the balancer/flywheel as an external balance.  Reason being is that this is sometimes much cheaper to go this route with aftermarket parts than balance internally which can mean adding heavy mallory metal to the crankshaft which gets expensive.


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## BLK69JUDGE (Jun 10, 2010)

*Hello*

you mentioned you have a cast flywheel ....

so I am using an unturned factory original 68 flywheel ...

I am kinda familiar with the muncies and stick cars as my 3 cars are all factory sticks ..
and I have taken a few apart also ...

so heres my take .... the 1" shanks are too long

too much threads hang out thru the crank ..... 

here is a few sets of factory flywheel bolts ,,,, and they are shorter than some
of the repops sold .... I think the repops are MOPAR also and reboxedfor pontiac...

if you have an aftermarket flywheel/steel flywheel they are even thinner in the hole
mounting flange .... 
whole different story then for adjusting the pivot ball to compensate...

I hope your cast flywheel still has a nice bevel on the edge similar to mine ...

once the bevel is gone.... the fly wheel is thin and the possibility of failure and also the springs on the disc hitting the bolts as mentioned above ....

I have a set of bolts with shiney heads that show contact with the disc springs ...

Scott
[email protected]


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