Exhaust Manifold bolts

[Rob M.]

I have reproduction bolts from LIC for the exhaust manifolds on my 300 hp car. I noticed that they are slightly longer (maybe 1/8") than the original bolts. Questions:

Is that just another reproduction vs. original variation? And, is there any concern using the longer reproduction bolts causing problems (cracking the manifold, or . . .)?

Should I just use the old originals?

Thanks in advance

[Joe L.]

Re: Exhaust Manifold bolts

I have reproduction bolts from LIC for the exhaust manifolds on my 300 hp car. I noticed that they are slightly longer (maybe 1/8") than the original bolts. Questions:

Is that just another reproduction vs. original variation? And, is there any concern using the longer reproduction bolts causing problems (cracking the manifold, or . . .)?

Should I just use the old originals?

Thanks in advance

Rob------


I would use the new bolts. Exhaust manifold bolts are hardened by the high heat and cooling cycles they experience. The hardening makes them more susceptible to breakage.

I don't think the extra 1/8" of length will cause you any problem as long as the bolts don't bottom in the threads (which I don't think they will). However, if the extra length bothers you, you can easily trim or grind it off. No one will ever see it.

[Rob M.]

Re: Exhaust Manifold bolts

Joe,

Thanks, I'll go with the new.

I didn't see torque specs in the AIM for the bolts. I did see 20 ft. pounds in the CSM. Is that the correct torque spec for the exhaust manifold bolts?

Rob

[Terry M.]

Re: Exhaust Manifold bolts

Joe,

Thanks, I'll go with the new.

I didn't see torque specs in the AIM for the bolts. I did see 20 ft. pounds in the CSM. Is that the correct torque spec for the exhaust manifold bolts?

Rob

There are no torque specifications in the AIM for the exhaust manifold fasteners, and many other fasteners, because they were part of an assembly (in this case the engine assembly) and were installed elsewhere (in this case at the engine plant). Now if we had the engine AIM (and that is a whole other story ) we would have those numbers. Use what you find in the CSM.

[Joe L.]

Re: Exhaust Manifold bolts

Joe,

Thanks, I'll go with the new.

I didn't see torque specs in the AIM for the bolts. I did see 20 ft. pounds in the CSM. Is that the correct torque spec for the exhaust manifold bolts?

Rob

Rob------


You won't find it in the AIM because the manifolds were installed at the engine plants. The correct torque is 20 lb/ft on the OUTSIDE bolts (the two bolts on each of the end exhaust ports) but 30 lb/ft on the two bolts at the center of each manifold. I know that 20 lb/ft seems unusually low for a 3/8-16 bolt but that's what GM says is right. That may be a big part of the reason for the french locks on the end bolts.

[John H.]

Re: Exhaust Manifold bolts

Now if we had the engine AIM (and that is a whole other story ) we would have those numbers.

Terry -

My wife drew (manually) many of the isometric illustrations for the engine plant A.I.M.'s when she was a technical illustrator and graphic line artist at GM; no, she didn't take any of her original "D"-size illustrations with her when she left GM.

[Terry M.]

Re: Exhaust Manifold bolts

Terry -

My wife drew (manually) many of the isometric illustrations for the engine plant A.I.M.'s when she was a technical illustrator and graphic line artist at GM; no, she didn't take any of her original "D"-size illustrations with her when she left GM.

Engine plant AIMs, as I said are a whole other story.

[Rob M.]

Re: Exhaust Manifold bolts

Thanks Joe!