valve stem oil seals

[doberman]

is it possible to replace the inlet valve stem oil seals without removing the cylinder heads?

[vee12eman]

Hi Doberman,

Now I should qualify this answer with the fact that I have not done this myself on a Jag V12.... However, referring to the manual, I don't think it would be easy, but is probably possible. The Cylinder heads have a known propensity to stick fast to the block and in particular, to the studs of the V12 and sometimes, even with the correct head removal tool and experience, they just won't come off, so it would be an advantage to be able to do this job without removal of the heads.

You will need some fairly flexible rope, which you insert into the sparkplug hole with the camshaft removed and the cylinder a little way down the bore. Bringing the piston up the bore by rotating the engine will compress the rope against the underside of the valves, allowing you to compress the valve springs using a lever - have a look at operation 12.29.18 of the original workshop manual (if you haven't got one, then don't start stripping the engine down!), this shows the correct valve spring compressor in action, you should be able to manufacture something similar. On other engines I managed with a crowbar under the head of a bolt screwed into a nearby threaded hole, but I wouldn't recommend this on an alloy head of an engine as complex and expensive as the Jag V12.

You MAY be able to gently lower the piston to drop the valve a little futher down the guide to make removal of the seal easier, but this is risky as you may lose the valve down into the piston bore which means the head has to come off. Because the valves actually descend in a different plane to the piston, it may also be a little difficult to push them back up by rotating the engine - try a slim, strong magnet to assist if this is the case.

If you don't feel confident, don't try it unless you are prepared to risk being forced to remove the heads. I was assured my engine had been treated well, but when I had it rebuilt, it absolutely refused to release one head and I now have a later engine fitted, albeit with the internal components of my old engine fitted. The guy rebuilding my engine has a great reputation, all the correct tools (including some from the original production line) and has been working on these engines all his working life, having started on the V12 production line in the 1970s, so he knew what he was doing and it still defeated him.

Good luck and let us know how you get on if you decide to have a go.

Regards

[PeterCrespin]

Minor point - the valves do move in the same plane as the piston on all Jaguar V12s. Not on XKs of course. I still wouldn't lower the piston because it's safer to pick the seal off one way or another. Do not mark the valve stem as it will wreck the new seal lip.

[doberman]

Hi Simon,
Well that is a novel way of changing the seals.
I will certainly give it some thought

Thanks for your reply
Doberman.

[snowdmc]

Hi Doberman,

If you're anywhere near the chalfonts, i'd recommend having a chat with Tom Barclay, he is an etype specialist and his garage is in denham, near the airstrip.

My Series 3 is there currently with the heads being taken off for a loose valve seat. he may be able to offer some advice.....

[doberman]

Hi Doberman,

If you're anywhere near the chalfonts, i'd recommend having a chat with Tom Barclay, he is an etype specialist and his garage is in denham, near the airstrip.

My Series 3 is there currently with the heads being taken off for a loose valve seat. he may be able to offer some advice.....

Hi snowdmc,
Thanks for your reply.As it happens i don't live too far from the Chalfonts
so i may call in at Tom Barcly's workshop

[alexb1406]

This can be done as I've done it - not just on V12's but on various other cars. I use a compressed air supply connected to the spark plug hole - I modified a compression tester to do this. Remove the camshafts first - all valves will be closed so the compressed air will build pressure and hold the valves in position. Remove the buckets and place a large socket over the valve springs. Give it a sharp tap with a hammer - make sure the socket is sitting squarely on the top - and this should break the seal on the collets. Then improvise with something to compress the spring and if space is limited you can use a magnet to retrieve the collets. Seals can now be replaced. Even if the valve moves a bit the compressed air immediately pushes it back into position. I've done this many times and never had a valve drop yet! Now...that's tempting fate next time!

One word of warning though - timing chain tensioners on the V12's can get very brittle with age and often break when attempting to retract them. This is a major operation involving the removal of either both heads or the sump - the sump may be easier but you have to remove 3 studs on each side that go through the heads - take care not to damage the fronts of the head gaskets.

[doberman]

Hi Alex,
I have heard of doing it this way before. But as yet I have'nt
decided what to do.

Many thanks Doberman.

[42south]

I did the job recently with engine still in the car. Briefly
lift tappett covers, just slide the cam sprocket onto the holding studs, dont touch the tensioner.
lift the tappett block off. Carefully note which way round the cam retaining shells go on.
use rope inside the cylinder to hold valves up, very easy just feed it in until no more will go in. It doesnt need to be very tightly packed. I didnt use air to avoid problems with fittings and the possibility of failure.
we used an old 6 cylinder valve spring compressor, with no problems.
with the spring compressed use a small magnet to lift the colletts.
I used 5/16x.500 Viton stem seals, they come with a small spring around the neck and are much more durable than the original.
I put stem seals on both the inlet and exhaust valves.
once all buttoned up again rotate the tensioner release to allow it to take up the slack.

Most important!
Go over to the jag lovers website and download Kirbys book of knowledge for the XJS, it's free, which describes the job and some suggestions for improvements to the cam cover rubber bung, and some other things. I found this book great in many areas

[abowie]

I have done this on a Honda OHC engine using compressed air to hold the valve up.

You can buy a brass connector that screws into the spark plug hole with a male fitting for your compressor hose. Screw it in, pressurize the cylinder and Bob's your hairy Aunty.

Disclaimer: mileage may vary, valves may fall etc