Aluminum Head question

[Warren F.]

In my continuing search to find NOS parts, I ran across a new in the box 3946074 aluminum head. Did the factory install heli-coils in the rocker arm threaded holes? I don't remember seeing this before.

[Clem Z.]

Re: Aluminum Head question

In my continuing search to find NOS parts, I ran across a new in the box 3946074 aluminum head. Did the factory install heli-coils in the rocker arm threaded holes? I don't remember seeing this before.

yes as i never saw a over the counter 074 had without heli coils in the rocker studs and with roller cams springs the exhaust studs still pulled out unless you used a stud girdle

[Wayne M.]

Re: Aluminum Head question

In my continuing search to find NOS parts, I ran across a new in the box 3946074 aluminum head. Did the factory install heli-coils in the rocker arm threaded holes? I don't remember seeing this before.

Warren -- I'm almost certain that heli-coils were installed when the new heads were in the machining process. My June-Sept 1967 dated '842' heads have them, and I read somewhere (can't recall) that only the 1967 MY Aluminum heads; the '392's', did not have them, or they were added in late production of the 392.

[Warren F.]

Re: Aluminum Head question

Thanks, Clem and Wayne. I've been amassing the original hard to find parts for my LS6's, such as dual disc clutch assemblies, 263 coil assembly (from original low mileage cars), distributors (with correct vac can), NOS camshaft & lifters, etc.

This aluminum head was in a well worn GM box sealed until the owner opened it up for pictures. I've owned several sets of these heads used that were in very fine condition but always had the rocker arm studs installed and I never removed them, so I didn't know. This particular head has the right date code as I have seen on real original LS6 cars, so I was very interested in it. My cars still retain their original GM configuration, so finding a head that hasn't been milled, surfaced or ported since new is really difficult.

[Wayne M.]

Re: Aluminum Head question

Warren -- no luck in finding that reference as to when heli-coils started in BB aluminum head rocker stud bosses, but did come across an article by Roger Gibson in Summer 1991 RESTORER. (bracketed items added by me).

"The rocker arm studs are also different on aluminum heads. The threads going into the head are longer. The use of the shorter stud will usually result in breakage of the boss. The longer stud has been discontinued from GM [ Gr 0.429, #3904396 (long) replaced by #3921912 (short) on 11-68]. They now have a kit to put steel threads in each boss [mandatory to install #452716 with latter stud]. This enables the use of the shorter studs. However, the longer studs can still be obtained through aftermarket suppliers."

So I'll guess that 1971 era production (and service) '6074' heads have the short stud with the heli-coil.

[Wayne M.]

Re: Aluminum Head question

-- I'm almost certain that heli-coils were installed when the new heads were in the machining process. My June-Sept 1967 dated '842' heads have them, and I read somewhere (can't recall) that only the 1967 MY Aluminum heads; the '392's', did not have them, or they were added in late production of the 392.

FOUND THE REFERENCE --- Chev Tech Service Bulletin 67-T-53, Sept 7, 1967. Subject: Rocker Arm Stud Pulling.

"396 and 427 engines with aluminum cylinder heads built after May 22, 1967, incorporate helical inserts in the rocker arm stud holes"

"with helical insert installed, the stud torque should be reduced to 50 ft.lbs."

So about half of the 392's, all of the 842's and 6074's had heli-coils from the General.

[Warren F.]

Re: Aluminum Head question

Wayne,

Thank you for your persistance in this matter! The NOS aluminum head should arrive on Saturday, it is my birthday present to myself since I turn another year older on Sunday.

[Patrick B.]

Re: Aluminum Head question

I have 6 "392" heads in my collection all dated between 1-13-67 and 3-14-67. All of them have all of the stud bosses heli-coiled.

None of these have a boss for a temp sender, but I used to have a 392 head dated 4-15-67 that had the temp sender boss and it was drilled and taped for the sender. In other words it was identical to a 842 head but it still had a 392 casting number.