Exhaust Ports Misaligned???

[stu in wichita]

I finally tracked down an annoying exhaust leak to an unlikely cause.  The #7 port in the exhaust manifold don't match the port in the head.   The engine is a 318 out of a 1970 truck with the original truck manifolds.

Compared to a gasket, the shape and size are correct, but the position is about 1/4" too far back.  The mating surfaces are nice and flat.  The misalignment is obvious when comparing the compressed area on both sides of the gasket.

I assume it's a bad manifold casting due to core shift or something.  It almost couldn't be the head, right?  I've never heard of anything like this.  I tried building up the area with weld and resurfacing it.  It sealed a little better (new gasket of course), but the tik-tik-tik is still there, especially until it warms up.

Any ideas? 

[Mopar Mitch]

If you're certain that its a '70 318, make sure that you use a set of exhaust gaskets for the 318.   Those ports are small vs the larger ports of the 340/360.  Also, sometimes the exhaust manifold's gasket surface could be warped from old age... check it... resurface if needed (local machine shop can do it).  Be sure that you're using the same port size for the heads and manifolds.

[70chall440]

Can you port match the manifold, meaning grind out enough to get the ports to match?

[stu in wichita]

Can't grind it to match.  The head port is actually open behind the manifold port.  I tried building up the outside of the manifold with weld, but didn't add enough material to completely close it.  Even if I build it up more, the misalignment makes the ports overlap, so the open area is somewhat smaller.  Not a big deal since it's not a performance engine, but I'm baffled at how this can be so far off.

All parts are definitely 318 with the small ports. 

This is only on #7 cylinder.  It's got to be a bad casting.  I just wondered if anyone had heard of such a thing.  I guess I need to find a different manifold.  Maybe someone on the forum has one.  Mot sure how many different configurations there are for early 70's manifolds.

Thanks for the suggestions. 

-Stu

[70chall440]

I cant say I have ever heard of this but anything is possible. Another option may be to make or have someone make you a adapter plate, you could gasket both sides and use longer studs. I really wish this site would take pictures because I'd love to see what this looks like, I am having a hard time visualizing what you are saying. Obviously the mounting tabs/holes are lining up, so in my mind what you are saying is that the port on the manifold does not cover the port on the head. This would suggest to me perhaps bad casting as you suggest - you didn't say but I suspect they were used, so that means they probably didn't have this issue from the factory, meaning that whatever they were on they fit. So, that means that the heads you have are different.