Exhaust down pipe gasket replacement advice

[XJR-S]

Well, my exhaust manifold-> downpipe gasket is blowing. Thank goodness not the manifold to head! So my question is, how 'flexible' are these exhaust systems? If I religiously spray the nuts over the coming weeks, undo it, will there be enough slack in the pipe to pull it off, clean it up and swap the gasket? Or will I have to look further down this rather rusty exhaust and undo something? The Cat to midsection clamps are pretty much hanging if I'm honest. Unlikely to undo with any ease after hitting many road humps.

So will I get away with it? I've been quoted about £100 for a garage to do it. But I don't trust this one not to slacken it off and pack a load of paste in there till it doesn't leak...! Which wouldn't last for long.

[oldtimer]

Hi,
There is no gasket in that joint in terms of a copper asbestos gasket. It is a steel olive - do I need to explain? The inside diameter slides on to the down pipe. The outside is a nice radius. The manifold has a matching radius into which half the olive sits. The down pipe has a flange into which the olive/sealing ring sits. Beneath the flange is a securing plate. Locate the down pipe into manifold, lift the securing plate onto the securing studs and wind on the nuts. I think that is about right without looking in the book.

Sounds dead easy, don't you believe it. First problem is gaining access, from the top or bottom.
Personally I would go from below with the vehicle on the lift using a long extension bar

Depending on your luck, will the nuts come off, with luck the studs will come out with the nut rusted to the stud. At worst is to shear off a stud then you are in trouble.

Don't forget the down pipe is a Y pipe so double trouble

With regard refitting you may find it necessary to dress down the stubs of the Y pipe in order to locate them correctly into the manifold. Extra long Brass nuts may be a good replacement.

If it is an offside pipe, Before removal of the down pipe check it's current position as there is limited room between the tower of the power steering rack and the chassis rail. Heat from the exhaust cooks the top seal in the rack tower.

Good Luck

Oldtimer

[XJR-S]

Excellent, thanks for that. I've got the same kind of figment on one side of the v6 on my other car. I've always used a bead of exhaust paste around to help it seal. Perhaps that would help in this case too.

[PaulGover]

Hi,
There is no gasket in that joint in terms of a copper asbestos gasket. It is a steel olive - do I need to explain?
...

Actually, it's asbestos (or possibly glass fibre or similar these days) filled, inside a thin steel shell, so they do compress to fill the gaps, assuming the joint surfaces are clean and undamaged.

The steel olives are between the joints in the exhaust pipes from the downpipe onwards.

You can put exhaust sealing paste (the Jaguar manual mentions the white paste you can get from Halfords and similar, rather than the grey "Gun gum" type) on the joint, but that will make it harder to dismantle next time, and it shouldn't be necessary if you can get a new olive in place and the joint properly and uniformly tightened. Sadly, that can be a big "if"

[oldtimer]

Hi Paul,
You are absolutely correct, it is a compressible copper/ asbestos (or the like) ring. Silly 'ole me,

I had a look in my spares rack and found the olive that fits at the bottom but couldn't find a top ring.

Top ring Part No C 18405 , that No goes back to the dark ages, also available as Unipart No GEX 7259

Bottom Olive Part No C35401

I have noticed something interesting in the Parts book. XJ-S - HE. That Uk cars have four studs in the manifold and support plate. Whereas USA J Canada have only two studs. But it appears that the change co insides with the introduction of the Catalyst.

The reason I mention this, is that a member remarked on the BB how generous Jaguar were to provide two extra holes for studs in the manifold, so now we know! Something to do with change points

[XJR-S]

Hi Paul,
You are absolutely correct, it is a compressible copper/ asbestos (or the like) ring. Silly 'ole me,

I had a look in my spares rack and found the olive that fits at the bottom but couldn't find a top ring.

Top ring Part No C 18405 , that No goes back to the dark ages, also available as Unipart No GEX 7259

Bottom Olive Part No C35401

I have noticed something interesting in the Parts book. XJ-S - HE. That Uk cars have four studs in the manifold and support plate. Whereas USA J Canada have only two studs. But it appears that the change co insides with the introduction of the Catalyst.

The reason I mention this, is that a member remarked on the BB how generous Jaguar were to provide two extra holes for studs in the manifold, so now we know! Something to do with change points

Thanks for all your thoughts. I'm debating doing this myself against the £380 + vat the garage want for the job.

So am I right in thinking therefore, with the four holes in the manifold, if I shear off a stud, I can cut both down and fit brand new stainless engineering studs into the extra manifold holes and simply rotate the floating collar on the downpipe?

If so, even on the worst case scenario, this could be a passable job without taking off the exhaust manifold. When I had a snapped stud on my other car, I had to take a whole turbo charger off to get out a broken stud.