Exhaust valve stem length after cutting and refacing valve seat. whats too long?

Howdie, new guy here. I have a honest to god barn find. Found a 1956 XK 140 that hadn’t seen daylight for 50 years. I bought new exhaust and intake valves, two burnt exhaust valves. Exhaust valve seats had been somehow made “different” from what is functional. Anyway had to resurface and cut down the valve face to make it functional again then lapped them in. I need to know the “too long” stem length of the exhaust valves. This is not a “C” head. Standard exhaust valve. Can’t find any reference in my books. Any help appreciated.

IIRC, the distance between the assembled valve/keeper/retainer, w/o the bucket or pad, and the base circle of the cam, is 0.320".

That gets you into adjustment territory: If my memory is wrong, someone here will correct it.

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Thank you for that information and will use it in the next step. But for now I would like to know the distance from the end of the valve stem to the spring seat. (unassembled just placed. in guide.) I looked back at my first post and didn’t make it very clear, sorry. If too long then I’ll have to take off a little.

When you say this do you mean the valves that you purchased were too large in diametre?

Dave, the minimum thickness shim (or adjusting pad) that should be used is .085” - see page B.39 in the Service Manual.

If your valve seats have been ground too deep then you will not be able to attain the an exhaust valve clearance of .006” using the minimum thickness shim of .085”.

Thus, at that point your valve stems will be “too long.” Some will recommend trimming the valve stems or using thinner shims, but there are risks to those solutions. At that point, it’s best to bite the bullet and replace the valve seats.


I believe he saying that he had to cut the burned valve seats to the point that he is now concerned that the valve tips will be too close to the cams. He is looking for the tolerance dimension for cutting the valve seats. I think the best way to check that is to install the valve, spring, keeper and tappet with your smallest shim and measure the lash.

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Mike is right, except that you can use a tennis ball or similar to hold the valve(s) tight to the seat, then fit a slightly oily shim(so it sticks the the underside of bucket) and bucket, followed by the cam…base circle down, of course. Soooo much easier than installing springs. OH, and don’t forget to pray.

No, they were the correct size its just there has been a few people over the years wrenching on this engine and I believe the valve seats were ground to a unhealthy depth which resulted in poor sealing hence two burnt valves and loss of all compression in two cylinders.

Do you have access to the factory service manual?

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If you first install the valve spring retainer, that is basically the installed height of the valve spring. That is in the service manual, which I don’t have in front of me at the moment. That’s the only direct way to get to the dimension you are seeking.

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Thanks Mike. The only manual I had was for my old E-Type. I will use what u sent I really appreciate the effort and yes I do pray a lot I’ve taken the lords name in vain many times so far while shaking my head. Thanks again.

Not to worry: it’s not his name, just his occupation…:wink:

I would suggest that you would do far less future cursing and gnashing if you invested in a XK140 factory service and parts manuals.

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Now that the .320" figure has been confirmed, just install the cam, hold valve seated, measure gap from stem to base circle. You will need at least a .326" gap…less means remedial action.

I just posted the same question, I see we are on the same page to establish the seat depth.
This is the spec my machine shop is requesting.
Did you ever find that spec?

If you found your answer, please contact me at autoartdw@yahoo.com
Thank You!!!

Yep, found what I was searching for. The valve stem protrusion spec is 1.430 from tip of valve to spring pocket. Thanks for checking back.

Thank you Dave for the great follow up.

Daryl W. Wagner
Automotive Artistry
British Car and Bike
Restoration, Sales and Service
Hudson, Ohio 44236