XK valve cover machining error?

I had a persistent oil leak from the rear of my left cam cover that I was scratching my head about. On the third try (I’m a slow learner), I decided to measure the mating surfaces of the cover and head where the plug-with-o-ring goes. There was .065" discrepancy, the cover larger diameter than the head machining. This would make a step-off where the o-ring seals and could cause a leak. I’ve suspected this before, but never looked that close. I pulled out another cam cover and it’s exactly the same. Did Jaguar make a bad batch or are they all like this? I didn’t see anything in the archives about this, but maybe others already know.

Anyways, I glued a gasket shim into the cover and puckied it back up, put in the plug - no leak.

I do know that the 3.4 and 3.8 covers are different
Pat H

Wonder what is different, As I have both 3.4 and 3.8 and valve covers are the same.

Hi all,
I believe the difference is due to the take off for the tachometers; mechanical Vs electric.

The diameter if the cutout for the tach mechanical drive

Ron, this topic from several years ago contains photos of the original style square profile o-rings supplied to the 3.4 liter engine cam covers. This may explain why it is difficult to be leak free with the round profile replacement o-rings typically sold today.

That’s interesting and a good point - I have seen the square profile seals before and made inquiry to the vendors as to why they aren’t supplied with basically shoulder-shrugs for reply. They are also used in the oil pickup tube where it connect to the oil pump, the new ones in the kits being round and not a very good fit. This is especially problematic where the square groove is considerably wider than the o-ring profile, and I’ve had those tubes in and out several times trying different o-rings for fit. I’ve good oil pressure in my fresh engine, so a standard o-ring does work.

Still, I haven’t heard from anyone who has noted the machining discrepancy between the cover and the head where the o-ring seats. I’m wondering how widespread a problem it is. Maybe I’ll check that measurement on a couple more heads to see if it’s an odd head that I have.

I did check another head and the same discrepancy is there. The first was a 4.2 Mk10 head the second a 3.8 Mk10 head, several years apart.