C2 Manifold to Exhaust Pipe Nuts

[Joe L.]

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-----

Yes, these nuts appear pretty much identical in configuration to the original nuts as shown by Jim and Brian and confirmed by John. Your photo shows them much better than the photo on Paragon's web-site. On the web-site photo they appear, at least to me, more like the Stover style nuts.

As it is, I guess there were at least THREE different styles of the 3829086 exhaust stud lock nut used. The original style must have been the style shown in Jim's and Brian's photos. I think this style nut might be referred to as an "Oval C Lock".

The second style was the "Flex Lock". I mistakenly thought that this style was the "original" style (i.e. dating back to the early C2 era). However, it now appears that it was not used during the C2 era. I am virtually certain that this style was used from the early C3 era until I-don't-know-when. My recollection is that my 1969 originally used this style nut, although I think I pitched them years ago (although I might still have them in an old box of original fasteners). Terry also has confirmed that his 1970 has this style nut. Others have reported this style nut in the past, as well. It's very possible that it was used alternately with the aforementioned version of the nut during the C3 era, though.

The third style is the Stover style nut. GM sold this style nut in SERVICE under the original 3829086 part number for at least the last 20 years until it was finally discontinued a few years ago. It is possible that it was also used for later C3's in PRODUCTION. I have no idea about that possibility.

[Joe L.]

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

John------


Thanks VERY much. That helps tremendously. What you have described is a Stover style lock nut. This is exactly what GM sold in SERVICE under GM #3829086 for, at least, the last 20 years.

I figured that the GM spec for the 3829086 may have specified alternate acceptable configurations. Apparently, it doesn't, though. However, I wonder if the 1962-73 version of the nut was significantly different than the 1973 re-drawn version?

Also, I suppose it's possible that while the AIM's from 1963 to 1982 indicate the use of the 3829086 nut, perhaps some other nut was actually used alternately and/or exclusively at various times during the period.

[Gary B.]

Exhaust Pipe Nuts; Paragon vs. original; differences?

Guys,

So what's the most biggest difference between the Paragon nut that John shows and the original nuts that Brian shows? The tiny nubs on the nuts from Paragon? Or something about the geometry? The differences aren't really obvious to me.

Gary

[Michael H.]

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,

This is the exact same nut that I remember being used all through the 60's and into the 70's on new GM cars. I still have quite a few in my tool box from that era.
In the mid 70's, I ordered the part number shown in the AIM for this nut but the nuts that arrived were much different than the originals.

[Bob J.]

Re: Exhaust Pipe Nuts; Paragon vs. original; differences?

Guys,

So what's the most biggest difference between the Paragon nut that John shows and the original nuts that Brian shows? The tiny nubs on the nuts from Paragon? Or something about the geometry? The differences aren't really obvious to me.

Gary

The 3 depressions that deform it look different and origies don't have dots or Os at each corner of the hex to start with.Bob

[Timothy B.]

Re: C2 Manifold to Exhaust Pipe Nuts

I installed the Paragon parts (nuts) on my 63 and they were so tight I had to run a tap through them first to loosen the fit because I thought they were going to eat the studs.

Could the dots around the perimeter mean grade eight?

[John D.]

Re: C2 Manifold to Exhaust Pipe Nuts

John------


Thanks VERY much. That helps tremendously. What you have described is a Stover style lock nut. This is exactly what GM sold in SERVICE under GM #3829086 for, at least, the last 20 years.

I figured that the GM spec for the 3829086 may have specified alternate acceptable configurations. Apparently, it doesn't, though. However, I wonder if the 1962-73 version of the nut was significantly different than the 1973 re-drawn version?

Also, I suppose it's possible that while the AIM's from 1963 to 1982 indicate the use of the 3829086 nut, perhaps some other nut was actually used alternately and/or exclusively at various times during the period.

Hi Joe

With regards to the cone feature the drawing states "45 degree min.-shape of cone, flat or radius optional. So with the millions of these nuts GM was using from different suppliers couldn't both types be expected ?

Timothy the dots around the perimeter you describe are the crimps for the locking feature of the nuts. They are called prevailing torque nuts in the fastener world...

[Joe L.]

Re: C2 Manifold to Exhaust Pipe Nuts

Hi Joe

With regards to the cone feature the drawing states "45 degree min.-shape of cone, flat or radius optional. So with the millions of these nuts GM was using from different suppliers couldn't both types be expected ?

John------


Yes, I'd say that's very possible.

There's another instance I can think of with respect to significant variation in the configuration of lock nuts used by GM. These are the rocker arm nuts used for small blocks. The part number for the self-locking nuts from 1958 through 1991 was GM #3744341. The original nuts used on my 1969 small block were the Stover type (i.e. domed with 3 triangular "pinches" to provide thread distortion).

In the mid-70's when I purchased some under this same part number, the nuts were the "oval" distorted thread type (somewhat similar in configuration to the exhaust stud nuts pictured in this thread). Sometime later, I purchased some and, as I vaguely recall, they were back to the Stover type.

As far as I know, the big block nuts were always the Stover type.

[Brian T.]

Re: C2 Manifold to Exhaust Pipe Nuts

Isn't it a wonderful thing, that our hobby can provide this amount of entertainment, with all that is going on in this world! Love it!

[John D.]

Re: C2 Manifold to Exhaust Pipe Nuts

I installed the Paragon parts (nuts) on my 63 and they were so tight I had to run a tap through them first to loosen the fit because I thought they were going to eat the studs.

Could the dots around the perimeter mean grade eight?

someone on ebay had the Paragon nuts in huge quantity for mega bucks. That was when this post started.

So which one of you bought them as they are now gone.
Gary???

[Gary B.]

C2 Manifold to Exhaust Pipe Nuts; a-bay auction; not me

John,

I had nothing to do with the e-bay auction to which you're referring. I never saw it actually. I don't know why anyone would want a lot of nuts that have clearly been deemed to be incorrect.

Gary

[Michael G.]

Re: C2 Manifold to Exhaust Pipe Nuts

Joe,

Virtually all GM lock nuts like the ones you speak about had a very general specification for the range of "prevailing torque" that was the source of the locking performance. This meant that any one of three or four completely different means of deforming the threads was acceptable, so long as it met the spec.

Purchasing tended to switch between these types freely, as several vendors were involved, all of whom had their own preference for deformation style. It would have been very unusual to have a nut that stayed only with any style for any long period of time. I know, I constantly had to solve problems caused by these "innocuous" cost-saving changes.

In my opinion, as long as the vendor marking was correct for that period, and the general shape and plating were correct, I'd say It'd be impossible to say which prevailing torque feature was correct for any car.

I hope that helps.

Mike

[Joe L.]

Re: C2 Manifold to Exhaust Pipe Nuts

Joe,

Virtually all GM lock nuts like the ones you speak about had a very general specification for the range of "prevailing torque" that was the source of the locking performance. This meant that any one of three or four completely different means of deforming the threads was acceptable, so long as it met the spec.

Purchasing tended to switch between these types freely, as several vendors were involved, all of whom had their own preference for deformation style. It would have been very unusual to have a nut that stayed only with any style for any long period of time. I know, I constantly had to solve problems caused by these "innocuous" cost-saving changes.

In my opinion, as long as the vendor marking was correct for that period, and the general shape and plating were correct, I'd say It'd be impossible to say which prevailing torque feature was correct for any car.

I hope that helps.

Mike

Mike-----

The thing that I find really unusual about the "Flex Lock" style nuts (i.e. the nuts with the small "slits" around the reduced diameter crown) is that while they were, apparently, used for at least some early C3 exhaust manifold stud applications, I have never seen this type nut used for any other application on any Corvette. Perhaps it was a short-term "experiment".

[Alan D.]

Re: Marsden nut

Need a few myself for 64FI with N11, but here's what is confusing -

63-65 FI calls for 3814568 an integral hex nut 3/8 in G3.275

53-72 the 3829086 which is the subject item appears in my 64AIM for the reg exhaust and N14 (use "prod nut") however the N11 is not shown! Said nut, 53-72, is also listed in G3.613 as a zinc finish with anti-seize coating.

The nut for N14, 65-67, is listed in G8.916 and another possible nut for 70-72 is in G8.917 So some differences appear to exist for the non standard exhaust systems. The 3829086 just may be the general service replacement!

Interesting how these questions expand!

Sorry for delay - posted just after JD's post of Jan 19 @ 9:59 through my email so it got delayed big time. Don't do that any more.

[John D.]

Re: Marsden nut

Alan, I realize this long post is confusing. Joe Lucia mentioned that the '086 nut was or is the general service replacment and has been for at least 20 years.
Jorjorian told me that the correct nut for our 63 to 65 FI cars, etc has not been available for an eon. He also said no tool catalog will carry it.
The Paragon nut is the closest to the real deal although it's not correct either.
I have spent a lot of time going thru 5 tool catalogs and the bottom line is this. Zilch. Stover nut is the closest and it's far from correct.
The Stover nut seems to have vaious designs.
Since you are into hardware big time for your 64 Alan I highly suggest you buy some nice used originals.
I also went thru a 5 gallon jug of old hardware and came up empty. JD