C2 Manifold to Exhaust Pipe Nuts

[Gary B.]

C2 Manifold to Exhaust Pipe Nut; still want a good photo

Guys,

I'm getting dizzy from this discussion. Anyone have a good, close-up photo of the correct GM nut?

Gary

[Joe L.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

Guys,

I'm getting dizzy from this discussion. Anyone have a good, close-up photo of the correct GM nut?

Gary

Gary------


My RECOLLECTION of the nut is that it was configured like the nut shown in the McMaster-Carr link I provided. I don't have any of these nuts, so I can't confirm its exact configuration (I've never used a lock nut for the exhaust stud application since these things can be nearly impossible to remove after heat and corrosion sets in). It's very possible that there were some nuance differences between the nut pictured and the original nuts.

There are several different styles of the "Flex Lock" nut. The Marsden style is, as I recall, more-or-less configured like a standard hex nut with "slits" at the top. I seem to recall that the original nuts had a crown configuration that was otherwise different than a standard hex nut. Whether it was a reduced diameter (like the McMaster-Carr nut), a dome, or some other configuration, I just do not recall for sure.

I'd be interested in seeing a photo of the original nut, too.

[Jim D.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

This is what is on my 65. The manifolds have never been off and the header pipes appear to be original but I can't swear these are original.

[Joe L.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

This is what is on my 65. The manifolds have never been off and the header pipes appear to be original but I can't swear these are original.

Jim-----


Very interesting. This is a "distorted thread" style nut. It's what I previously described as the "later version" of the 3829086. However, as I also mentioned, I think it's very possible it was used ALTERNATELY in PRODUCTION with the "Flex Lock" style. Your installation might be an indication of that.

Even if the exhaust pipe has been off the car at some point, it's possible the nuts were re-used.

Just one comment here, though: the exhaust pipe flange seen in your photo is not the configuration I would expect. However, it's very possible that style was used during the mid-year period. Perhaps others more familiar than I could comment on that.

[John D.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

I wish I could take a pic of the one on my 63 but can't. The original does not have the "slits". Otherwise the basic configuration is similiar.
The original is not so heavy duty-has less meat on it than the one in the nice photo that Joe supplied the info for.
Ones that I bought from a Corvette catalog were actually a hex stover locknut which is incorrect. Locknuts with the slits in them are incorrect.
Looking thru MSC Industrial Supply I clearly see the one we are looking for is not shown.
On the other hand MSC has some nylon insert hex locknuts listed as "standard, heavy thick, heavy thin and thin". Page 1942 of the 2009-2110 catalog. The standard locknut photo is the much closer than Gary's photo but still not correct.
Now I can see why a Corvette repro catalog whould list the Hex stover locknut. Not saying it's right but saying it would fly for most except for us nut cases. JD

[Joe L.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

I wish I could take a pic of the one on my 63 but can't. The original does not have the "slits". Otherwise the basic configuration is similiar.
The original is not so heavy duty-has less meat on it than the one in the nice photo that Joe supplied the info for.
Ones that I bought from a Corvette catalog were actually a hex stover locknut which is incorrect. Locknuts with the slits in them are incorrect.
Looking thru MSC Industrial Supply I clearly see the one we are looking for is not shown.
On the other hand MSC has some nylon insert hex locknuts listed as "standard, heavy thick, heavy thin and thin". Page 1942 of the 2009-2110 catalog. The standard locknut photo is the much closer than Gary's photo but still not correct.
Now I can see why a Corvette repro catalog whould list the Hex stover locknut. Not saying it's right but saying it would fly for most except for us nut cases. JD

John-----


How do your originals compare to the ones that Jim posted photos of?

[Jim D.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

Jim-----

Just one comment here, though: the exhaust pipe flange seen in your photo is not the configuration I would expect. However, it's very possible that style was used during the mid-year period. Perhaps others more familiar than I could comment on that.

According to the JG, the 2" manifolds use a 1/8" stamped steel flange and the 2 1/2" manifolds use a 7/16" thick cast or forged flange, like mine.

[Gary B.]

How many judging points are we talking about for the nuts?

Anyone care to venture how many point deduct we're talking about if one used the McMaster-Carr Flex-Nuts instead of the original GM nuts? The 63-67 scoring sheets for Mechanical, Exhaust Manifold section allocate 5 originality points for:

Bolts, studs, nuts, flanges, locks, washers & heat riser

Could the total deduct for close, but incorrect nuts be 1 full point?

Gary

[Brian T.]

Re: C2 Manifold to Exhaust Pipe Nuts

As I was working on a photo, I see that another has been posted. Anyway, here is another, and these are just like what I have on my 66 Bowtie car.

[Jim D.]

Re: C2 Manifold to Exhaust Pipe Nuts

Thanks for posting those pics. Brian. They confirm that mine are original.

[Joe L.]

Re: C2 Manifold to Exhaust Pipe Nut; still want a good photo

According to the JG, the 2" manifolds use a 1/8" stamped steel flange and the 2 1/2" manifolds use a 7/16" thick cast or forged flange, like mine.

Jim----

That answers it. Thanks. I think I've got it figured out now. 63-82 with 2" exhaust used flange GM #3734402. This is the stamped steel flange with the curved, reinforcing lips.

1965-67 with 2-1/2" exhaust used flange GM #3850231. This is the thick, flat flange as seen on your car.

1968+ with 2-1/2" exhaust used flange GM #3915125. I think this is the stamped steel flange with curved, reinforcing lips (i.e. configured like the 3734402 except for 2-1/2" exhaust). This style also became SERVICE for all 63-67 with 2-1/2" exhaust after August, 1971.

I mistakenly though that the 65-67 2-1/2" used the same style as later. Now I know better.

[John H.]

Re: C2 Manifold to Exhaust Pipe Nuts

Here's the Paragon nut - it's about as close to the original configuration as you're going to find. I'm not familiar with the details on C3's, but when I was running Chevrolet engine dress lines and chassis lines in the mid-to-late 60's, my guys installed hundreds of thousands of those prevailing-torque Stover manifold nuts, and the photo below (and the ones Brian posted) is what they looked like. I've never seen any split flex-lock or Marsden-type nuts in a Chevrolet assembly plant for that application, at least through 1967.

[John D.]

Re: C2 Manifold to Exhaust Pipe Nuts

As I was working on a photo, I see that another has been posted. Anyway, here is another, and these are just like what I have on my 66 Bowtie car.

Brian, The original nuts on my 63 FI car are identical to yours.
Thanks, John

[John D.]

Re: How many judging points are we talking about for the nuts?

Joe Lucia, etal. The original nuts shown in the two photos are identical to the ones on my car except mine are cad plated.
I spent a lot of time looking thru various industrial catalogs and also a 1979 Standard Parts book and could not find the correct nut.

I did see one nut in MSC that looked to be somewhat closer though but didn't mark down the info although I mentioned it in a previous confusing post of mine. JD

[John D.]

Re: C2 Manifold to Exhaust Pipe Nuts

Hi joe

The drawing for 3829086 drawn in april 1962 and redrawn in febraury 73 shows a 3/8 nut with a 45 degree cone at one end. It goes on to say the locking feature shall consist of two or three equally spaced constrictions located in the cone shaped area. hope this helps

jd