Greetings O' Wise ones....
After giving my Cylinder Head a good ignoring for a bit I recently tried to get interested and 'got busy'.

Ok, I've been 'flip-flopping' about whether to change the Valve Stem Oil Seals in the replacement head that I got.
Although the head has had work done to it (skimmed and had the Inlets opened/polished) I tried to use that as justification NOT to replace the seals as I couldn't really be bothered with removing 24 valves and I reasoned that the valves will have been removed when the work was done.

A couple of weeks ago I had my head (the one attached to my neck) under the bonnet and an elderly gentleman walked past and struck-up a conversation. It turned out that he used to work as a Jaguar mechanic 50 years ago and knew the workings of the older straight 6 engines (XK..??). I told him of my dilemma about whether to strip the Head and he said ' yes - of course you should. If it's on your bench and you already have a set of new seals then just do it..!!'
So I did.
And he was correct.
I found two of the seals on the Inlet side had split from top to bottom.

Before I removed the Cams I did a quick check of the Valve Clearances and found them all to be a bit tight - the book says clearances should be between 0.3mm and 0.36mm. Roughly a half of mine were around the 0.25mm and the rest about 0.3mm but nothing bigger than that. Could this be by design..?? Would the tighter clearances be beneficial for a (slight) performance head..?? Or is it more likely that the shop that did the work re-lapped the valves but didn't adjust the shim thicknesses to suit..??

Anyway, I've built the head back up and rechecked and the clearances are still the same - I did hope that the Garage Elves would have sorted it out for me while I slept one night but they didn't....

As always - your thoughts would be appreciated,

Cheers Dave.

 

I read this a while ago and now again, and feel I should put my 2 cents in. If the valves were lapped and opened etc, would that not increase the clearance? I havent done such things myself so I may be way off..And.. Did you use the same feelers each time? Just putting it out there. Good Luck.

 

Jerry, last time I lapped valves was in 1975 so maybe I'm not the best person to reply either ...however, seems to me that if the valves were freshly lapped in, that would bring the butt end of the valve stem closer to the cam lobe and therefore less clearance?

Larry

 

Gents,
Yes - you're both absolutely correct. Lapping the Valves will bring them closer to the cam and reduce the clearance. Not by much though.
I gave the valves a quick lap - just enough to get a nice, continuous ring - and it made zero difference to the 'before and after' clearances.
This is what's making me think that the shop that did the Head work used a machine or a drill etc.

What's the opinion on my valve clearances..?? The book says they should be 0.3mm (just less than 0.012") to 0.36mm (just over 0.014")
Roughly half of mine are at the minimum - 0.3mm
but the other half are under the minimum at 0.25mm (just less than 0.010")

Am I worrying about nothing..?? We're only talking about 0.05mm (0.002") or should I try and find an Engineering shop that can grind a couple of thou off my shims..??

Cheers, Dave.

 

Of course. Closer. What was I thinking.
Different thickness of shims can be had from the usual suspects. I'm not sure I would chance it. But at the same time the chance of my being in that situation are minimal.

 

Agree with Jerry, after all that work get the correct shims - why risk it for the sake of a few inexpensive parts.

Larry

 

Fair point Gents - new shims it is (really surprised at how NOT inexpensive they are - the cheapest I can find are over £4 EACH..... That's around the $5 mark, all times 24 )

Just for the record - I found a post on another forum that states to aim for the greater clearance of 0.36mm at least as the 0.3mm figure is too tight.

So that's it then - i'll throw more money at it.

Many thanks for your input.

Cheers, Dave

 

You can move most of the shims around and buy the few that don't work or you can 'BUTT the stems' of the valves to increase the 'lash' on the ones too close.

Lot's of ways to refresh a cylinder head. I have done many over the years.

bob

 

As you're in the UK maybe contact these guys - I have a feeling the shims might be less expensive than from the dealer..

BTW -let us know if you go that route, OK?

https://www.enginepartsuk.net/valves...-shims-springs

Larry

 

Dave,

If you'll search the archives at the Jag-Lovers forum, you may find that a member there created an Excel spreadsheet for figuring out how to move your shims around to work on most of the valves so you only have to order shims for the few cylinders you don't have appropriate shims for. The member who created the spreadsheet may have been Dave Lokensgard but I may be wrong. The post probably dated to the late '90s or early '00s.

Cheers,

Don

 

Don - it's the work of Nick Saltarelli - here it is

Valve Shimming Algorithm and Spreadsheet Tool (Zip File - 10KB)

Larry

 

Larry, Don & Bob,
A genuine 'Thank you' for your help.
I've got a miserable 10 straight days at work starting tomorrow.
Once that's out of the way I'm going to hang a 'Do Not Disturb' sign on my garage door, put some 'R.L. Burnside' on a little too loud, fire up a cigar (Alcohol can stay away..) and get measuring.....
I'll keep you informed.

Cheers, Dave.