XK engine valve clearance service interval?

Did Jaguar have a regular service interval for valve clearance (lash) check and adjustments in any versions of the I6 XK engine? Or was this typically done because of a problem or when other engine work was done?
I just reviewed the original “Passport To Service” for my 1984 XJ6 Vanden Plas and adjusting valve clearances is not mentioned for any of the Service Intervals through 105,000 miles.
BTW, after one burnt valve, a few leaky head gaskets, and some leaky cam shaft cover gaskets on my three running XK engine Jaguars, my gut feel is that checks should be done somewhere around every 60K miles because I have seen valves close up a bit after that. If 100K miles were driven without a check I would feel I am living on borrowed time. This is for a normal street not for racing.


I would regularly check every 10,000-20,000 miies: not often did I find one seriously out of spec, but I know I averted disaster on a couple, by finding closed-up exhausts.

We know it important to check the valve clearances, but did Jaguar include the valve clearance check/adjustment during any Service Interval?

It seems that they should have, but I can’t find it in any of my manuals that I looked through, and I have a large collection of manuals from the XK120 to the Series III XJ6. They all include the procedure, but I can’t find a Jaguar specified Service Interval. Maybe it was just done on exception? When something was wrong?


@Dick_Maury will likely have an answer. I was wholly unconcerned with it, since I just had customers on a regular preventive maintenance schedule.

Properly done, I regularly see valve jobs go 100,000 miles with less than .001" variance in clearance. You will get some seat and valve seat wear. This will be offset from the adjustment shim wear and usually evens out. Not a bad idea to check the clearances when replacing valve cover gaskets. With the new Cometic gaskets, that is something that does not need doing as often as the old days. The later camshafts with the .012-.014" clearance are very sensitive to tight clearances. When the front cam bearing wears and one goes to tighten the upper chain, you can actually close up the clearance on the front cylinder adjustments. I have seen this actually cause the front cylinder to be inactive at idle. And along those lines, the later cams run a lot better if adjusted at the .014 spec. They are not any louder but idle a lot smoother. This applies to the V12 also that uses the same style camshaft. The camshaft for the early V12 Non-HE vs the HE engine is the same. The clearance spec changed but the cam did not. (6 liter is different). Set the HE to .012 and it will idle like a dream.


Thank you for your insights. Is it fair to say that Jaguar did not specify XK engine valve clearance checks or adjustments during any specific Service Intervals? That they were done if problems were encountered where a technician suspected an engine valve problem or when other engine related work was done?


Paul, the highest wear item on the XK head was and is the guides. Once they start to wear, the valve does not hit the seat properly and as such, does not cool properly and wear/pitting occur. However, even valve guides will easily go 100,000 miles with proper oil changes and proper tune. Bronze guides last even longer than the OEM cast iron ones. I also see a lot of worn out exhaust guides where shops put on stem seals. Jaguar did start putting them on the exhaust side on the later XJ40 but never on the XK engine.

About 35 years ago, Yamaha started selling their 10,000 rpm FZR bikes as being set for life. Everybody scoffed but it turned out to be effectively true. A couple of years ago I had reason to take the head off my 50000 mile Triumph and was amazed to find that not only were all the clearances perfect but 11 of 12 shims were identical and the 12 the was only half a thou different. Jag metallurgy wasn’t as advanced but I could imagine them only being set if noisy or during some other work.

My Hyundai, with hydraulic tappet buckets, and a 16-valve is still silent and runs like a champ, at 232,000 miles.

The car has essentially no residual market value, so if it ever decides to fail me, I’m thinking I want to take it apart to see what caused it to keep running…:wink:

Yeah, well, hydraulic tappets is cheating :slight_smile: I bet you don’t use manual timing or mixture control either.

Kids today, they don’t know they’re born…

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My 17 year old son is learning to drive. As natural smart arse he told me that driving is “easy”. A few lessons in our 5 speed Subaru Forester took the smirk of his face.

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I went to school with a lad called Terry Breen. Nobody ever accused him of being a smart-arse. Good footballer though.