Midyear small block Carburetor to Intake Manifold studs - Are these originals?

[Scott S.]

I'm working on a '67 L79, but the question may be applicable to other midyear small blocks.

The nut to the carburetor studs is called out (UPC 6-C2), but no item or part number is called out for the studs. Since the L79 does not use a Baffle (heat shield), does it take a shorter stud than the 300hp? I did not see any description for these studs in the JG.

The studs that were in my aluminum intake manifold have a dimple in the 5/16-18 end, and the 5/16-24 end (the nut end) is dished. Overall length is 1-1/2". Does anyone recognize whether these are original?


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[Timothy B.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

My 67 is 300hp and I will measure the stud sticking up, it will be later today before I get back to you. I can't imagine the 350hp car any different, that stainless shim (300hp) is very thin so I don't think it makes any difference in 1967.

I don't know if the parts book calls out a different #.

[Joe L.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

My 67 is 300hp and I will measure the stud sticking up, it will be later today before I get back to you. I can't imagine the 350hp car any different, that stainless shim (300hp) is very thin so I don't think it makes any difference in 1967.

I don't know if the parts book calls out a different #.

Timothy-----

The same part number is shown for all applications in SERVICE in the P&A Catalog. It is possible, though, that different studs were used in PRODUCTION for the 2 applications. I HIGHLY doubt it, but it is possible. The studs were installed at the engine plant and are thus not shown in the AIM.

[Scott S.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

My 67 is 300hp and I will measure the stud sticking up, it will be later today before I get back to you. I can't imagine the 350hp car any different, that stainless shim (300hp) is very thin so I don't think it makes any difference in 1967.

I don't know if the parts book calls out a different #.

Tim and Joe,

The parts book is a little confusing (to me) on this one. In group 3.288 it looks like 1963 Corvette with H/Per. uses what are called "1st design" 5/16-18-24 x 2-9/16" studs. Then 63-65 Corvette (327 with H/Per.) use what must be the "2nd design", 5/16-18-24 x 1-53/64" studs.

Finally, "55-67 ALL, Corvette" shows 5/16-18-24 x 1-9/16" studs, GM 3836527. This would seem to cover all applications not specifically designated otherwise in the two entries above (e.g., 1963-1967 250-300hp, 1965 L78, 1966-67 L79, L36, L68, L71, L72, L88, L89).

This same part number (GM 3836527) is then listed in Group 3.335 for 63-65 Corvette, and finally listed again in group 8.981 where it's a little shorter (5/16-18-24 x 1-1/2") and we find out it's made of 260-M (grade 5) steel.

Tim, do yours look like the ones in my pictures, with a smooth section separating the two different threads, the dished end visible, and the dimple end (presumably) screwed into the intake manifold?

[Scott S.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

The studs were installed at the engine plant and are thus not shown in the AIM.

Joe,

I can see 'em, they're just not identifying themselves. It seems like the AIM never gets tired of playing that trick on me

I thought I read that the dimple end should be facing up, but that won't work with the old carburetor studs. When I had my intake manifold restored, it came back with new studs installed, and the new ones do have the dimple-end facing up.

Is either one correct? What is typical factory production configuration and finish for these studs and carb nuts?

[Joe L.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Tim and Joe,

The parts book is a little confusing (to me) on this one. In group 3.288 it looks like 1963 Corvette with H/Per. uses what are called "1st design" 5/16-18-24 x 2-9/16" studs. Then 63-65 Corvette (327 with H/Per.) use what must be the "2nd design", 5/16-18-24 x 1-53/64" studs.

Finally, "55-67 ALL, Corvette" shows 5/16-18-24 x 1-9/16" studs, GM 3836527. This would seem to cover all applications not specifically designated otherwise in the two entries above (e.g., 1963-1967 250-300hp, 1965 L78, 1966-67 L79, L36, L68, L71, L72, L88, L89).

This same part number (GM 3836527) is then listed in Group 3.335 for 63-65 Corvette, and finally listed again in group 8.981 where it's a little shorter (5/16-18-24 x 1/2") and we find out it's made of 260-M (grade 5) steel.

Tim, do yours look like the ones in my pictures, with a smooth section separating the two different threads, the dished end visible, and the dimple end (presumably) screwed into the intake manifold?

Scott-----


I don't see where it's confusing. The listing for 63-65 Corvettes can be completely discounted since as far as I know what we're talking about here is 1967 Corvettes. That does not mean that the same stud(s) used for 1963-65 were not used for 1967, though. It just means that a listing for 1963-65 applications is irrelevant when we're concerned about 1967.

As far as the listing of the 3836327 for ALL, Corvette 1955-67 applications that means that this stud is the SERVICE part for "1955-67 ALL, Corvette" applications. The term "ALL" used in the P&A Catalogs excludes Corvette. The addition of the term "Corvette" to the term "ALL" means that all models included in that edition of the P&A Catalog are covered.

Very often, but not always, the terms "ALL" or "ALL, Corvette" implies a part that that can SERVICE all the applications but is not necessarily the part that was used in PRODUCTION for all the applications. A bevy of closely configured parts may be consolidated into just one part number for SERVICE. For PRODUCTION GM might not want to have extra long, exposed studs as they convey a "un-factory-like" build. For SERVICE, the extra long studs are unimportant---they work just fine. By the time the car needs SERVICE parts, it's already sold!

[Joe L.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Joe,

I can see 'em, they're just not identifying themselves. It seems like the AIM never gets tired of playing that trick on me

I thought I read that the dimple end should be facing up, but that won't work with the old carburetor studs. When I had my intake manifold restored, it came back with new studs installed, and the new ones do have the dimple-end facing up.

Is either one correct? What is typical factory production configuration and finish for these studs and carb nuts?

Scott-----

Don't worry about the "dimples". These studs have fine thread on one end and coarse thread on the other. The coarse thread goes into the intake manifold. Thus, there's no way the studs can be installed incorrectly OR any way other than the way they were originally installed. Period. This may even be why GM used different thread on either end to avoid the studs being installed incorrectly on the assembly line (remember, orientation is important here because the thread length on either end is different).

I have seen these studs both phosphate-finished and zinc plated. I don't know which one is correct for any particular application OR whether one or the other was exclusive to any particular application.

[Timothy B.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

I just measured the studs on my 67 300hp engine and there is 1 1/4" sticking up from flush with the manifold. I did not remove one to measure total length but it's probably safe to say there is 1/2" screwed into the manifold so total length is 1 3/4" long. That would be 1/2" course thread, 1/4" unthreaded and 1" fine thread, (total 1 3/4"long)

I did not notice any dimples on the top and they are black plated.

[Scott S.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott-----

Don't worry about the "dimples". These studs have fine thread on one end and coarse thread on the other. The coarse thread goes into the intake manifold. Thus, there's no way the studs can be installed incorrectly OR any way other than the way they were originally installed. Period. This may even be why GM used different thread on either end to avoid the studs being installed incorrectly on the assembly line (remember, orientation is important here because the thread length on either end is different).

Joe,

I understand the threads only allow the studs to go in one direction, but I have examples now of two different kinds of studs, and if it's like almost everything else on these cars, one is probably correct and the other is wrong.

It's not really about points or judging, although I'd rather get it right now instead of fixing it later. Having the car judged seems to be the best way to get a thorough and knowledgeable evaluation of what I got wrong and what still needs to be fixed, so for that reason I'm looking forward to it. Since the whole car is apart now, it makes sense to get as much of it right as I can. A big part of that process has turned out to be figuring out what's "original" and what had been replaced over the years. It's mostly about wanting to know how it really was, and then putting it back together that way. In theory, if I do that reasonably well, the points will take care of themselves. The objective is to get as close to an "original production" 1967 Corvette as I can. Then put some good tires on it, and drive

[Scott S.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

I just measured the studs on my 67 300hp engine and there is 1 1/4" sticking up from flush with the manifold. I did not remove one to measure total length but it's probably safe to say there is 1/2" screwed into the manifold so total length is 1 3/4" long. That would be 1/2" course thread, 1/4" unthreaded and 1" fine thread, (total 1 3/4"long)

I did not notice any dimples on the top and they are black plated.

Tim,

Thank you very much for checking. The new studs that were installed when the manifold was restored stick up 1" from the manifold surface. For the old (unknown origin) studs, the portion that would be above the surface of the manifold when installed measures about 1-1/16".

[Scott S.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott-----


I don't see where it's confusing. The listing for 63-65 Corvettes can be completely discounted since as far as I know what we're talking about here is 1967 Corvettes. That does not mean that the same stud(s) used for 1963-65 were not used for 1967, though. It just means that a listing for 1963-65 applications is irrelevant when we're concerned about 1967.

I only included the info about 63-65 Corvettes because I know Tim also has a '63 in addition to his '67, so I wanted to show that the P&As differentiated between the carburetor studs used 63-65 and 66-67.

As far as the listing of the 3836327 for ALL, Corvette 1955-67 applications that means that this stud is the SERVICE part for "1955-67 ALL, Corvette" applications. The term "ALL" used in the P&A Catalogs excludes Corvette. The addition of the term "Corvette" to the term "ALL" means that all models included in that edition of the P&A Catalog are covered.

Thank you Joe, that's good to find out.

I thought "ALL" meant all, and wasn't sure why sometimes it was followed by "CORVETTE", and other times not. Now I understand (better!)

[David L.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

I have collected many original carb studs from Chevrolet and Corvette intakes over the past 30+ years but mainly in the 1980's. All I could EASILY find are the studs pictured below.

Early 1963 300 HP C.I. intake, cast. # 3799349 dated K122 (Nov. 12, 1962),
measured 1.77" OAL, 0.50" long coarse threads, 0.97" long fine threads, "dimple" on bottom end.

Early 1966 B.B. C.I. intake, cast. # 3866948 dated I245 (Sept. 24, 1965),
measured 1.31" OAL, 0.45" long coarse threads, 0.54" long fine threads, "dimple" on top end.

Dave

[Timothy B.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

Hopefully some other owners will post the details and length of the stud on original cars. I will find out what's on a 65 350hp car that is very original and post back.

Can anyone say if these carburetor studs used a thin nut. I keep thinking the hold down nuts were the thin style.

[Joe L.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

Hopefully some other owners will post the details and length of the stud on original cars. I will find out what's on a 65 350hp car that is very original and post back.

Can anyone say if these carburetor studs used a thin nut. I keep thinking the hold down nuts were the thin style.

Timothy-----


According to GM the GM #120368 nut was 0.27" thick.

[Scott S.]

Re: Midyear small block Carburetor to Intake Manifold studs - Are these originals?

Scott,

Hopefully some other owners will post the details and length of the stud on original cars. I will find out what's on a 65 350hp car that is very original and post back.

Can anyone say if these carburetor studs used a thin nut. I keep thinking the hold down nuts were the thin style.

Tim,

The AIMs call out the same GM 120368 part number for the carburetor nut from 1963 through at least 1969. In the '67 AIM, this same Nut part number is also called out for the unidentified fan clutch to fan blade studs, and also secures the hose clip to the front of the A6 compressor.

FWIW, AMK shows this part number as being 5/16-24, Grade 5, 1/2" across the flats, .27 thick. Their photo shows what appears to be a standard height hex nut.



Edit: just saw Joe's post, looks like AMK has this one right.