Cannot find it in my notes.
What should the bolt torque be when using the original iron Exhaust Manifold/Bolts to an Aluminum Cylinder Head? I know it's gotta be less than the cast iron Cylinder Head number, but by how much? Using Fel-Pro MS9275B gaskets.

Thanks much.


Steve

 

Steve, are you using bolts, or studs?

GUSTO

 

I'm not an 'engine builder'; I'm an Engineer. But this issue is a very important one.

Cylinder heads have a lot of [explosive] force that needs to be retained. Whether the head is steel or aluminum, it has to retain the same force. Steel bolts are quite capable of handling those stresses.

However, retaining an almuminum head with steel bolts creates a significant problem: aluminum expands at about twice the rate as steel when temperature is elevated...and cylinder heads do get HOT!

Since the heads need to expand (after being assembled at room temperature), it would be BEST that the bolts retaining that member expand along with them. But steel bolts expand at twice the rate of the heads. So, the steel bolts will place added [compression] force on the heads at the points of contact once they reach engine operating temps.

ARP has dealt with this by having special steel washers that are placed between the bolts and heads for the purpose of assuring accurate torque application. Other builders deal with this in different ways.

I'm diving into this issue so that those wanting to put aluminum heads on their car's engines will take adequate caution by using proper means to assemble aluminum heads with steel bolts. It's important to get this one right so that head cracking/bolt loosening issues do not occur.

 

Hi Gus.

Stock bolts, that came with the ramhorn manifold.

Steve

 

I hear ya 71.
These Exhaust Manifold Bolts were constantly loosening. I looked at the washers on these bolts closely this time, and their Lock washer warp, I call it, was totally absent. Time with the heat probably done them in, as far as temper was concerned, so I now replaced them. I'm anxious to see it the loosening will be curtailed for a while now.
ARP does seem to be the Leaders in this racket. I trust them too.

Thanks for the insight.


Steve

 

the 1969 factory shop manual lists 20 ft/lbs for all V8s which would have included the factory aluminum heads

 

Thanks Mel.

In my '73 GM Shop Manual, I found 30 ft/lbs for the "inside bolts" and 20 ft/lbs for obviously the outer port bolts.

Perhaps I should try 20 all around, and check for leaks afterwards.


Steve

 

I've always had good luck with tight. Then tighten again after a heat/cool cycle. Repeat several times.

 

I found the same thing for small block but gave you the big block number since that had the aluminum heads in 69.

 

The engineering "issue" with this is:

At the proper rated bolt torque (when cold), can the heads go thru a full heat cycle (engine fully warmed up then go back to ambient temp) without any permanent deformation of the bolt (permanent stretch) or permanent deformation of the aluminum under the bolt/washer?

If the head material and the bolt are limited to "plastic" deformation and fully return to the original state after a heat cycle, the bolts SHOULD not loosen.

In many cases, pros will lock-wire or put French locks on the header bolts; but I have never seen anything like that on the head-to-block mounting bolts.

 

When I'm dealing with aluminum heads or engine blocks I use studs wherever possible. And then I coat their threads with Permatex Aviation Form-A-Gasket so moisture can't get in. And when using bolts I make sure the thread engagement is at least twice the bolt's diameter so a 3/8" bolt would screw in at least 3/4".

 

I thought about Safety Wire (drilling the bolt heads), but couldn't see an acceptable way to wire them. French Lock concept would work. Are they commercially available for the ram-horn manifold, or would I have to fabricate them?. Wouldn't mind doin' that.

Steve

 

Studs.

I like that idea, as well as the sectional density concept.

Steve

 

Thanks Mel,

It is a 383, with components that push the compression ratio up there pretty high.

Steve

 

SB ramshorn manifolds had French locks put on them from the factory. They are readily available from Corvette parts supply sources.

 

Thank you sir.
I'll look for them.

Steve

The one's I've found look like they only cover the 4 "inboard" bolts, and nothing for the two end Exhaust Manifold Bolts.

 

There should be (1) French lock installed for each pair of bolts at each exhaust outlet.

 

This is how I would safety wire it if you're using bolts.

Just loop it from one bolt to the next one around the manifold.

If you're using studs with nuts, there is a fixture you can use to drill the the corners of the nut.


Good luck... GUSTO