Thinner than usual valve pads

[Philippe-J.]

I would like expert's opinion about the minimum thickness of valve adjusting pads.
As a matter of fact, after regrinding of the valve seats, and change of valves for new, I measured that the normal pads, minimum thickness of which is 0.085" = 2.16 mm, would be too thick for my engine. Using a thin dummy pad, I inferred that I would need pads as thin as 1.34 mm. The thicker one should be 2.01 mm.
My question is, assuming I find someone able to machine such pads from commercial ones : is there any inconvenience running an engine with 1.34 mm thick pads?
Thanks for your thoughts.

[mgcjag]

Shims fit on the top of the valve and are above the collar...too thin a shim will sit below the collar and cause serious issues....I dont know what the thinnest shim possible is...you could easily measure it....remember that shims are hardened so grinding them down removes the hardened layer.....iv heard of some skimming the tappet...speak to your machine shop.....sounds like you need new valve seats....Steve..ps 1.34mm I think is way too thin....lightweight thinner tappets from later models are an option....you would need to search

[chrisfell]

Generally speaking, for an engine where valve seat recession results in needing shims less than .085”, it is time for a cylinder head rebuild.

Queue shipwright’s disease.

[Stevemorris]

I had the same issue.

SNGB have had smaller shims made, you are correct they only used to go to 0085” but I got a 0.076”. As Steve said make sure the shim is not too thin so the bucket pushes on the valve spring cap though.

I’d suggest that SNGB have not gone any lower than 0.075” as a standard valve stem sits almost below the level of the spring cap if it goes any lower?

I managed to knock 0.006” off my original shim using an oil stone, took an hour though!!

See here…

viewtopic.php?f=8&t=21986

[Philippe-J.]

I just had the advice from a mechanic shop. According to them, shims thinner than 2 mm = 0.078" would be risky.

Question # 2: would shorten the valve stems be an option?

[mgcjag]

No that is not an reccomended option....Steve

[Philippe-J.]

I could have bet
Thanks anyway.

[johnetype]

You certainly can shorten the valve stems by a certain amount - when I had a late large valve head rebuilt recently, they removed the same amount from the end of the valve stem to equal the amount the valve face lapping had moved the valve up by to save finding new shims - but I doubt you could shave the nearly 1mm you need off without causing problems.

[Stevemorris]

As Steve said, definitely do not shorten the valve stems. You could loose the hardness but more importantly the valve stem will be sitting too low in the spring top, which means the bucket may be in contact with it and not directly the shim/valve itself.

The gap is too small because the valve seat has been subjected to years of hammering and the proper fix is to renew the seats.

Not sure who is recommending you the minimum thickness but SNG Barrett are a recognised Jaguar parts supplier and I would suggest if the minimum thickness is what they are suggesting then SNGB wouldn't supply 0.075" shims?

I fitted an 0.076" shim to mine and it's fine. I am planning to remove the head over winter and replace the seats so this for me is a temporary fix.

Hope this helps,

Steve.

[Philippe-J.]

All of yours answer do help, fore sure
All my problems come from the first workshop I gave my head to restore to. They stopped their work in the middle of the river, leaving me with new guides and reskimmed valve seats. They said they had no time to finish it up. So now I myself have to deal with valve seats, (new) valves, collars, tappets and shims with one of them being wrong, but which one?
Anyway, the safer way to go seems to be having another (more reliable) workshop install new seats with the right depth wrt to the valve I have now, doesn't it?

[Stevemorris]

Yes, sadly you will not be the first to be the victim of someone who doesn't know what they are doing...

The seat height is crucial on these due to the availability of shims. 1.34mm equates to a 0.053" shim, and the smallest available is 0.075". Get new seats fitted by someone who knows the product is my advice...

Best regards, Steve.

[Philippe-J.]

Thanks Steve,

I'll go to another (approved) workshop and discuss with them.
Let's hope the bill of valve seat renewing won't too heavy , summer holydays are pointing ahead

Regards.

[Gfhug]

Philippe, you know Rory, don’t you? Why not ask him for local advice or he may suggest you send/bring the head to one of two British companies. CMES at Bracknell or Rob Beere in Coventry.

Bonne chance

Geoff

[Stevemorris]

Years ago (1980's) I used to work in London and serviced/maintained/restored these cars all day every day. We used to use Board Brothers, Clapham. They were old school and did countless XK head/block/crank stuff for us.

The son (Phillip) is still around and working from a place in Sussex, he quoted me £500 for new seats/Guides and head skim. That was including the parts. I can send you his number if you want Phillipe.

Best regards, Steve.

[Philippe-J.]

Geoff,

yes there is a part of luck in the restoration process, and I'll need some! Luckily there is the forum and all its participants to help

The first hurdle is to get the right advice about:
- what is the thinner safe pads? --> answered
- can I shorten the valve stems? --> answered here, but ambiguous elsewhere (i.e. one of the major part supplier)
- how much will it cost to renew all the seats? --> partially answered, let's

The second hurdle will be to find the right workshop --> my first attempt failed completely . I'll be considering your suggestions, thanks for them.


Philippe

[Philippe-J.]

End of the mystery: I eventually found the cause of the issue about the valve pads: the valves I had through the french workshop are too long.



New on the left, old on the right.

Also note the geometry of the stem tops, that wouldn't ensure the pads to seat well in tappet recess cause the groove for the cotters is too low

The solution is then to buy a new set of six inlet + six exhaust valves. I'll go to Rob Beere as every one say he is reliable.
Normally I won't need to renew the valve seats , which is a relief.

to all for helping.

[Gfhug]

Philippe, when you talk to Rob ask for the rubber inserts that go on the inlet valves and anything else he suggests to get all working nicely. My recent experience with him is that he and Carl will happily spend time explaining things, over the phone or via email.
Let us know how it all goes.

Geoff

[Philippe-J.]

Thanks for the advice Geoff, I'll do that.
Regards.

[mgcjag]

Would be interesting to know where those "new" valves are from...do you have any info/receipts for them...Steve

[Philippe-J.]

Alas no, Steve. I tried to contact and ask the faulty workshop, but they are so busy that they have no time, apparently, to talk to me
I'll tell you if they answer, eventually.