XJ6 & XJ12 Series I, II & III 1968-1992

XJ6 Series 3 Valve Clearances.

 
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Old 08-04-2016, 12:02 AM
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Default XJ6 Series 3 Valve Clearances.

Hello folks,


Looking for some advise and there's no better place for Jaguar wisdom than here.


I'm currently rebuilding my Series 3 4.2 after a head gasket failure. Block and head have both been crack and pressure tested, both lightly skimmed and the bores honed.


The head has been re-seated for new valves and this is where my problem lies; I cannot fit any feeler gauges between the camshaft heel and bucket. Camshafts have new bearings and are correctly torqued down.


Is there a 'base' size shim I should be using? What is the minimum clearance I should be aiming for?


My second problem, according to the engine shop, was the failure of a composite head gasket. They suggested I use a MLS or copper gasket instead. Has anybody else been told similar, or have experience with non-composite head gaskets?


I tried contacting Cometic here in Australia but received no reply back from my queries, re using a 040" thick MLS head gasket and whether this would affect compression ratio.


Or do I just use another regular head gasket and hope for the best.


Any advise or feedback would be greatly appreciated.


Cheers.
 
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Old 08-04-2016, 03:01 AM
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This will be time consuming.

Strip the camshafts, gather the shims, and measure what you have.

Take the thinnest shim, and then one at a time fit that known shim to each valve position, measure what you get, and thus calculate the shims needed.

Lots of writing and calculating will be needed.

The fact teh shop has " recut" the seats, which is normal, the clearences that were there prior to dismantling are gone.

Worse case, is the tip of the valve stem MAY need to be slightly skimmed to achieve the gap you need. Sadly the valves will need to come outof the head to do taht skim.

I have always used teh composite head gaskets, no issues. They will fail eventually no matter what is used.

I will assume the timing cover was bolted in place when the block was refaced???.
 
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Old 08-04-2016, 12:05 PM
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Originally Posted by Grant Francis View Post
This will be time consuming.

Strip the camshafts, gather the shims, and measure what you have.

Take the thinnest shim, and then one at a time fit that known shim to each valve position, measure what you get, and thus calculate the shims needed.

Lots of writing and calculating will be needed.

The fact teh shop has " recut" the seats, which is normal, the clearences that were there prior to dismantling are gone.

Worse case, is the tip of the valve stem MAY need to be slightly skimmed to achieve the gap you need. Sadly the valves will need to come outof the head to do taht skim.

I have always used teh composite head gaskets, no issues. They will fail eventually no matter what is used.

I will assume the timing cover was bolted in place when the block was refaced???.

Thanks Grant,


I will follow your procedure and then visit Sovereign's for new shims. This rebuild has been interesting to say the least, so hopeful the valve stems don't need to be skimmed.


And yes, timing cover was in place when block was refaced.


Cheers.
 
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Old 08-04-2016, 03:19 PM
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Hi to all, using a composite head gasket would still be my call. try using Permatex "Copper Spray a Gasket" to give the new gasket some extra strength. I have used it in various road and race applications and have never had a problem.
The valve shimming dilemma is never a fun job and as Grant has stated its a long slow process and may take a couple of goes to get it right. Even consider taking old shims to your engine machinist to have them milled down can assist unless you have a good selection of sizes to try.
Good luck with it, you will achieve your goal in good time
 
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Old 08-07-2016, 03:23 PM
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Originally Posted by Dr Phill View Post
Hi to all, using a composite head gasket would still be my call. try using Permatex "Copper Spray a Gasket" to give the new gasket some extra strength. I have used it in various road and race applications and have never had a problem.
The valve shimming dilemma is never a fun job and as Grant has stated its a long slow process and may take a couple of goes to get it right. Even consider taking old shims to your engine machinist to have them milled down can assist unless you have a good selection of sizes to try.
Good luck with it, you will achieve your goal in good time


Thanks for your feedback, will give the copper spray a try when it comes time to reunite the head and block again.


Cheers.
 
 

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