Hi-

I'm having a bit of a problem reattaching my exhaust pipe to the exhaust manifold at the flange on a 225 slant 6 on a 73 Swinger.
I took the manifolds off to replace the gasket between the two manifolds, which was blown out.
I also needed to replace the intake to exhaust manifold bolts.

I reinstalled the manifolds and am trying to re-bolt the pipe to the exhaust manifold at the flange.
Somehow, when I try to do this, there is now a gap at the center of the flange, so that there is an exhaust leak flange.
It is as if either the base of the manifold or the flange of the exhaust pipe is cupped so that the two surfaces meet only where the bolts are.

But when I check the flatness of the flange with a ruler, it seems like it is quite flat to me.
It's hard to check the surface at the manifold since it is upside down now - but when I had it off the car, I looked at it, and it seemed like it was OK.

Before removing the manifold from the exhaust pipe, there was not an exhaust leak there - so I assumed it would be fine putting it all back together.

I am not sure how this could happen, and i'm not sure how to correct the problem, either.

I'd appreciate any ideas anyone may have.
Thanks!

I rechecked the exhaust flange. Though the flange itself is flat, somehow the entire flange seems to be shifted and on a very slight angle relative to the end of the exhaust pipe - so that on one side of the flange the end of the exhaust pipe is flush, and on the other side the end of the exhaust pipe is slightly below the edge of the flange. It isn't even all the way across. What this creates is a gap of about 1/8" to 3/16" on the one side of the flange, even with a new gasket on there and the exhaust pipe bolted up.
I don't know how it got like this, but the flange doesn't seem to be budging if I try to push it back to where I think it should be.

I think I probably have to go to an exhaust shop for some help here.

Try loosening the other end of exhaust pipe ; at muffler and any holding bracket to give pipe
slack so you can position exh pipe flange flush with exh manifold. If pipe clamps are rusted
get new ones on hand, then apply penetrating oil on threads and let soak then loosen nuts,
if threads not to rusted you can loosen clamps , if it is too rusty then you have to cut them.