Exhaust manifold bolts in aluminum heads.

[Terry F.]

Anyone know if the same special bolts were used to attach the exhaust manifolds on 68/69 big blocks as were used in cast iron heads? Just wondering if the aluminum head used a different configuration. Thanks, Terry

[Dick W.]

Re: Exhaust manifold bolts in aluminum heads.

Terry, the fastner heads were the same and I would have to make the assumption that the fastener was the same.

[Terry F.]

Thank you! Terry *NM*

[Joe L.]

Re: Thank you! Terry

Terry-----

I believe that Dick is correct. HOWEVER, personally, I would not use these special, self-locking bolts, used for the end runner position on both sides, for retention of the exhaust manifolds on engines with aluminum heads. I think that it's too hard on the threads or, even, on the thread inserts (Helicoils) used on some aluminum heads.

For aluminum heads, I would use the 65-67 arrangement of french locks on the end runner bolts. Special bolts were not originally used for the 2 center runner positions on both sides.

I've already "evaluated" this issue for my own purposes with the "ZL-1" and after much "experimentation", research and "cogitation" came to the conclusions referenced in the recommendation contained in paragraph 1, above.

[Terry F.]

Re: Thank you! Terry

That's sort of how I felt. I was wondering how the aluminum would like those funny threads. Personally, I might use the bolts but tap the threads and install them with some mild lock tight or something. Thank you, Terry

[Steve Antonucci]

Re: Thank you! Terry

Joe,

What "special" self-locking bolt are you referring to? Why would the out-board
runner positions be any different that the in-board runners as relates to the bolts?

Lastly, what did the L-88's and ZL-1's use for exhaust manifold bolts?

Steve

[Joe L.]

Re: Thank you! Terry

Steve-----

Steve-----

Beginning sometime during the 1967 model year, if not from the outset of the model year, the french locks used for the end runner positions on the exhaust manifolds were replaced by special self locking bolts.

For the 1967-69 period, it MAY be that these self locking bolts were used for all manifold bolts (except those associated with special studs used N-40/C-60 applications) or it may be that only the end runner positions used the special bolts and the rest were standard bolts. Why? Well, IF it was done as I described, presumably it would have been done for the same reason that only end runner positions received french locks for 65-66.

In any event, I believe that for 67-69 most big block applications, Corvette and otherwise, received the special bolts. The EXCEPTION was L-88, L-89, and ZL-1. These applications received the special bolts only for the end runner positions and used standard bolts for the center runner positions. Why? Probably for the same reason that I am reluctant to use the special bolts for ANY position on aluminum heads.

For 1970-74 big block applications, all applications used the special bolts only for the end runner positions and used standard bolts for the center runner positions.