I was going through a vendors ads and they said that an exhaust manifold can shrink 3/8 of an inch and crack, or break bolts.How common is the problem?Has anyone had this happen?

 

It does happen periodically. Most of the ones I've repaired are on heavy haulers. It still takes a long time to happen though.

 

Mine's shrinking. The ATS is on my list of stuff to do.

 

mine's good and shrunk, but it's not leaking so I keep on drivin'

 

Yeah Ours is shrunk pretty good and it has pulled a bolt, getting ready to put a new in pretty soon. Its amazing how much they will shrink. But its a 91 with around 300,000 on it and we do some serious haulin with it.

 

How often does this happen? I doubt as often as some vendors would like you to believe. If you get an aftermarket manifold, it may require some serious work to get flows where they should be. Some of them are pretty restrictive or mismatched.

Carl

 

there's only one aftermarket manifold for these trucks... it flows well, but no better than the stocker...

and it doesn't happen as often as the advertising leads you to believe... yes, it hapens, but you can just visually inspect yours... if it's working well, leave it alone... if it starts leaking or it snaps a bolt, put an aftermarket one on it...

but I wouldn't replace a good working stocker just to replace it unless I was just bored and had the money.

Forrest

 

That was the answer I was looking for.I didn't think it was an overnight thing.Mine has a lot to be done before I worry about that,thanks.

 

yeah, if you've only got 110k miles on it, and it's stock, I wouldn't worry at all...

the 1st gens had big turbine housings and push less fuel than the 2nd gens... the exhaust manifold on my old 91.5 is still kickin' w/ almost 400k miles on it... and over 300k of that has been pulling big goosenecks.

now, the manifold on my 97 is a different story... it's got 235k on it, and it's shrunk probably as bad as the one on my old truck. but this thing is running a LOT more fuel through it and it's seen some high EGT's!

Forrest

 

A far more common problem in our 1st Gen trucks is manifold gasket creep.
The expansion and contraction cause the manifold gaskets to creep out. Look at your gasket on number 1 cylinder as this is often the most common one. If you see the gasket material protruding from the joint, you've got gasket creep.

Remove the manifold, use a good block sander with, oh say, 400 fine sand paper and dress the exhaust manifold surfaces.
Then, look for the two bolt holes that are smaller than all the rest. I think they are/near #3 cylinder.
Just try enlarge those two holes a tiny hair larger.
After that, do you gasket install. Once you're done start the truck, warm it up to operating temp then shut down and let it cool to rougly 100*F
Go back over your bolts and tweak the torgue and after that you should be good to go.
OH .... the most common cause of the creep is higher boost pressures/high EGT's.