I installed new exhaust manifold gaskets about 4 months ago (1955 Tbird 292).   I tightened them down and after running it a couple of times I tightened them again.   I checked them this weekend and a couple were not tight, they needed 1/8 of a turn.   I heard if you tighten them too much the manifold could crack.

I obviously have to go a little tighter, is this common?   I thought I read someone else had a similar issue.

I'm no expert, but the 292 in my hot rod does the same thing.  Every few months or if I hear a "leaky exhaust sound," I'll just re-torque them.  

Someone here will likely have a real fix.  

One of the speed shop parts catalogs may still offer ‘locking’ manifold bolts. Once snugged down on the gaskets and locked with their central allen/hex bolt, no leak noise after 70K miles/20 yrs.for me.

6 VOLTS/POS. GRD. NW INDIANA

Are you using lock washers ?  The star lock washers may work better that the usual  lock washer.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

You don't want to use a composition gasket on an exhaust manifold as this will be the result. The cyl head and manifolds expand and contract at differing rates causing the loosening.

It is metal to metal or steel shim if needed.

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6 VOLTS/POS. GRD. NW INDIANA

No problem with using the composition gaskets.  I have used them on both of my yblocks with no problems - leakage or breaking.  If you install the manifolds   correctly, I doubt you will ever have broken ear.  I use lock washers on all the bolts.

54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

I am using flat lock washers with Felpro exhaust gaskets