I have removed the cracked exhaust manifolds from my XJ6 (1995, X300, 4.0 US model). The previous owner failed to achieve the proper seal between the exhaust manifolds and downpipes to precat (small catalytic converter, first one after exhaust manifold) and gave up. It seems to me that each downpipe consists of a couple of pipes, once inside the other with a doughnut-shaped seal in between them. I suppose that as the flange gets tightened the doughtnut-shaped seal will get squeezed between the inner and the outer pipes forming a seal against the manifold.

The problem: As the previous owner tried to tighten the flange,he bent the studs and messed up the threads, but failed to move the inner pipe into the proper position where it would form a seal. I am suspecting that the pipes might be frozen together. Is there a trick or a technique to forming this joint? Should I try to free the pipes before attempting to tighten the joint up?

I also found some info suggesting that a different was used in different markets. Namely "slip joint" vs. "doughnut type". If someone could shed some light on this I would really appreciate it.

 

I am a little confused as to which joint you are referring to.

The 'downpipe' from the manifold incorporates 2 cat converters. It seals to the manifolds with 2 'donut' type seals (or 'olives' in Brit speak, item #2 in the picture below).


Exhaust Pipe-Front-3.2/4.0 Litre-Catalyst-Not Japan - Parts For XJ Series from (V)720125 to (V)812255 (X300) | Jaguar Heritage Parts UK


In the illustration seal #6 forms the joint between the headpipe and the underbody exhaust peipe (which includes another car converter). The seal fits into the bell-shaped ends of each pipe and the clamp actually pulls the two pipes together against the seal when it is tightened.

Some cars don't have the #6 seal. The pipes just slip togother, one inside the other. This is the slip-joint type.

Does any of this help?

Cheers
DD

 

Doug, thanks for your help, I appreciate it. I am talking about part #2 - the 2 'donut' type seals/olives that seal downpipes to manifolds. I am guessing I incorrectly called it a slip joint, creating the confusion.

I looked at the downpipe, and it consists of an inner pipe and an outer pipe with the dount/olive squeezed between them. The inner pipe goes inside the cast iron manifold, the outer pipe goes to the precats. The olive is squeezed between them when you tighten the downpipe flange to the manifold. The inner and outer pipes are supposed to move relative to each other as you righten the flange, if I understood this design correctly. It looks like they might be frozen together on mine. I'll make some pics tomorrow.