Exhaust manifold broken

[davidr]

I was going to do a 5 minute job on my V12 coupe at the weekend as I had my pit open to do a service on my wife's Land Rover. I had an annoying rattle that felt and sounded like the exhaust touching a heat shield on occasion. So I thought a quick look underneath, give a few things a bash with a rubber hammer, find the culprit and adjust. Easy enough - 5 minute job!
Oh no! I quickly established that the rattle wasn't underneath but was the heat shield attached to the exhaust manifolds on the passenger side. OK I thought. The bolts must have come loose so I'll just do them up and happy days.
That's when I found that they wouldn't move! They're quite substantial so I thought a big breaker bar was the way to go. The amount of effort needed was considerable so I thought I'd better take them out and see what's going on.
The issue turned out to be that the bolt was a 1/2inch UNF that had been forced (and I mean FORCED) into an M12 threaded hole.
This is one of the perils of the XJS for the unwary - the threads are all sorts! For example the threads cut into the top of the manifolds that hold the heat shields on are M12 and M8, the studs for mounting the manifolds to the head are M8 but the studs for the downpipes are 3/8UNF!! No wonder people get confused!
The trouble came when taking the smaller heat shield bolt out the casting fell apart. There had obviously been trouble before as there was a helicoil in there. Oh bugger! 5 minute job just got a bit more complicated!
So I've now got to find another front passenger side exhaust manifold and swap them over which is fiddly as the bottom nuts are very awkward to get to.
I've got the manifold off but it was fiddly. Anyone got any clever ways of putting the lower nuts back on more easily?

[steve_m]

Pay someone else to do it? Assuming it is driveable of course.
Jestyn at Thruxton Jaguar is pretty handy.

[Brakebuster]

bum

i think new manifolds are still available from the heritage site, the back left is the same as the front right , and vice versa , and are about £100 each

as for the nuts.....you'll have to use ' the force '

good luck

BB

[davidr]

Steve - thanks for the suggestion but the car is not driveable as I've taken the manifold off. I am aware of Jestyn at Thruxton but I usually go to Hollygrove in Ringwood when I need help and advice as Will there is a good friend. Usually costs me lunch though!!
Will has a couple of scrap engines so I'll take a manifold off one of those. He may even have one already removed as he has a huge stock of used parts.
BB - thanks for your suggestion but,as I say, Hollygrove will have one.
The nuts aren't impossible but they're just very hard to get to as you mostly cant see them or get a socket under there. As you say, I used the force to get them off so it looks like the same method to put them back on! Just thought that someone may have a better idea!

[oldtimer]

David,
Have you considered using brass nuts during assembly ?

[davidr]

Update - have now found a replacement manifold and have started the job of putting it back. I think I got a bit confused about the threads though. They should all be imperial after all. What confuses me is that M8 is very similar to 3/8" unf.
The issue with my car is that the large bolt on the rear manifold that holds the heat shield on should be 1/2" unf but I'd guess that there's been a problem with a stripped thread in the past and an M12 helicoil was inserted. But the 1/2" unf bolt was put back in and wouldn't tighten down properly. How this hadn't made a noise before in the 13 years I've owned the car I don't know. The only thing I can think is that I replaced the exhaust recently.
Anyway, the manifold is back on as of tonight but what an awkward bugger of a job. You can't see the bottom nuts, can't get a socket on them and there's hardly any room to get a spanner in there. Mostly did by using the force.The swear box is now overflowing!
Just got to put the downpipes back on and reconnect the exhaust and reassemble the various bits I took off for access and my 5 minute job will be complete 2 weeks later!

[davidr]

All back together again now. Took her out for a 10 minute test drive but I hadn't driven her for a couple of weeks, the Test match was on the radio and the sun was shining so actually was out for over an hour! She drove beautifully, the rattle was gone and we enjoyed our time together. God these cars get under your skin!!
The manifold I'd replaced, downpipes etc were all fine, no leaks and pretty quiet too.i just need to figure out why the other side is noisy. No leaks but just sounds a bit tinny and gruff. Never ends does it but that's part of the fascination.

[poprivet]

Has anyone wondered why the exhaust manifolds are in groups of 3 rather then being single ones of 6? Same goes for the 6 cylinder engine, the exhausts join further down the pipe.

Due to valve overlap, engines with more then 3 cylinders have more then one exhaust valve open at a time. If there was one manifold serving all 6 cylinders, back pressure from one of them would affect the exhaust of the other. Seperating them enables longer valve opening to optimise power and efficiency.

[davidr]

Thanks Pop - an interesting little snippet.
I've been thinking of gathering these little gems together for putting into the magazine so keep them coming!

[Tintin]

I've been thinking of gathering these little gems together for putting into the magazine

"Confessions of an XJS owner" - now there's a thought!

Robbie

[steve_m]

I think that Robin Askwith is a bit long in the tooth now to reprise his role.

[poprivet]

Maybe David can start a new thread, it would be interesting.

I owned my XJ-S for many years before realising that the drivers door mirror is fitted further forward then the passenger side. This is to give a unobstructed view rather then just being a hang-over of poor British Leyland workmanship.