Just though I'd update you on what's happenin with the XJ.
For compression tests on the 4.0l, the book says that anything from 120 to 150 is acceptable, with max deviation being 30 psi from any other cylinder. I did a compression test with these figures:
No. 1 - 90 psi
No. 2 - 160 psi
No. 3 - 155 psi
No. 4 - 160 psi
No. 5 - 165 psi
No. 6 - 160 psi
I then knew that I had an issue with no. 1 compression, hence the difference in spark plug colour that I'd reported a week ago. Compression didn't change with a little oil added to the rings (so rings are fine), so I thought it could be either a headgasket / cracked head (unlikely because it ran so well above idle) or a valve.
So the head came off friday night. A note here, you will have trouble taking out head bolt 14 (the rear LHS of the engine) as the bolt has an extention thread on it to accommodate the nut from an earth strap. In the end, I bought myself just enough room by dropping both engine mounts and lowering the whole engine / gearbox assembly to the point where the bolt / head combination could be tipped and manouvred out of the hole. That bolt needn't have been that long, so I have cropped about 25 mm off the extention thread to make it easier to re-install. I did spot flogged out left hand engine mount while doing this, much easier to fix now than later!
I took the lifters out, all convex faces, no scratches, etc,,, so they are ok. Headgasket was also good and not blown.
When you've gone to the trouble of getting this far into it, you may as well take the lifters apart and give each individual component a clean before putting it all back together again. These are fiddly and small components, and you should get instructions on how to re-assemble (i.e., oils, lubes to use).
Then did a water test on the head (re-insert sparkplugs, turn head upside down and then fill the concave part with water to submerge the valves). I found that after 30 minutes or so about 1/4 of the water in No. 1 head had dribbled out through the inlet port. So, No. 1 inlet valve face or valve seat is the culprit.
Next job is to strip the head and grind faces, etc as required to make it seal again. I will initially try this by myself using grinding pastes, but might have to get a valve or two ground in the headshop. Will re-assemble with new valvestem seals as they come in the kit anyway, so why wouldn't you, even if it isn't blowing smoke.
The point is, so far this has cost me about $70 for a VRS kit (valve regrind set, includes valvestem seals and all top-end gaskets except for the rocker cover gasket, which is re-usable), so you can do all this yourself in your own time as long as you are lucky enough to have the use of another car in the meantime!
Hope some of this helps some of you one day, you never know when it's your turn...
[ 01 September 2002, 11:27 PM: Message edited by: Kramer ]