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View Full Version : Exhaust Manifold Shrinkage????



Hock
03-11-2010, 02:37 AM
While I was in the middle of changing the valve cover and plugs on the driverside I noticed that I had a blown manifold gasket. Well after I was finished cleaning the mating surface on the manifold I went to reinstall it and the darn thing wouldn't bolt up. After checking it with the new gasket is saw that the front and rear ports had contracted inward about an 1/8" each making impossible to bolt it back on and more than likely was the reason (other than the possible loose bolt :D) the gasket blew in the first place.

Now the question I have is has anyone seen this before on these engines? I know SBC's are famous for this with cast manifolds. Even the extra one that I used has some shrinkage to it though not bad enough that I couldn't bolt it on.

Now after this experience and about 4 lost hours of my life that I will never get back I think I may be changing to headers sooner than later.

XR7 Dave
03-11-2010, 09:42 AM
If a bolt was loose for awhile and liquids have been spilling on it then yes, it is possible for them to shrink. If you force them back, they can and do sometimes crack. I would overdrill the holes on the one that fits better and leave it alone. Headers are more problems than manifolds so don't think that is a solution to your problems.

WhiteThunder
03-11-2010, 11:01 AM
I had that happen with an exhaust manifold when building one of the engines for my SC. The shop where I was working had a tool to specifically made solve that problem. I don't know what it was called. You put the tool between two exhaust manifold runners and turned it with a wrench. It would open and spread the runners until they were back in their stock spots.

90turbo1
03-11-2010, 11:43 AM
mine on drivers side did same thing.

just elongated bolt holes a bit and all was good.

believe it or not in snap on tools there is a tool to fit GM cast manifolds it spreads them open when reinstalling it.

mine were off about 1/8 as well. its a product of heating and cooling over and over and not enough support at the flanges it should have been made with a solid flange all the way across but there is packaging restrictions I bet.

Motohead
03-11-2010, 12:15 PM
I had that same problem before headers I bought one of these http://www.amazon.com/Lisle-LIS13000-Manifold-Spreader-Chevrolet/dp/B002XMW49I
It was years ago but I think I had to grind on it a bit to get it to work on the SC

WhiteThunder
03-11-2010, 12:45 PM
I had that same problem before headers I bought one of these http://www.amazon.com/Lisle-LIS13000-Manifold-Spreader-Chevrolet/dp/B002XMW49I
It was years ago but I think I had to grind on it a bit to get it to work on the SC

Yup, that's the puppy - an exhaust manifold spreader tool. (Ran down to the shop and took a photo of it.)

BECERRASC
03-11-2010, 08:57 PM
ok

when was rebuilding my engine i got into the same problem but my problem was the gaskets you guys compare the gaskets with the manyfold on the work table and you will see what i am talking about... either you cut the gaskets cause the holes on the gaskets don't match or don't use them this was feelpro gaskets ... take a look again compare them.... you'll see

Hock
03-11-2010, 09:22 PM
ok

when was rebuilding my engine i got into the same problem but my problem was the gaskets you guys compare the gaskets with the manyfold on the work table and you will see what i am talking about... either you cut the gaskets cause the holes on the gaskets don't match or don't use them this was feelpro gaskets ... take a look again compare them.... you'll see

Not in my case. The gasket was perfect. I grabbed the other manifold that I had and it bolted right up.