Machining Valve Stems

BACKGROUND. I purchased 4x V12 engine parts off of eBay a while back. The purchase included both left and right thermostat housings. The right housing still had the coolant temperature sensor in it. Bad news: it was stuck in there pretty good. After 8 days/nights of hitting it with PB Blaster, and “wiggling” on it each night with a 1/2" socket on a 1/2" drive ratchet, I finally got it to break free. The worse news: some of the aluminum threads came out with the sending unit. I took it to a local (Colorado Springs) machine shop to see if they could repair it. I wanted to rescue it cuz the eBay ad said it came off an engine with 18,000 miles. I don’t believe everything / anything I read in eBay ads but the condition of this housing is “new” – see photo which includes old sensor with aluminum still in threads.

They had the proper sized tap and were able to clean up the threads to the point I believe I will NOT need to use a heli-coil or aluminum welding to build up the material. Those options still exists if needs be.

VALVE DISCUSSION: in talking to the owner when I picked up repaired housing I mentioned setting up the aluminum heads with overhead cams {I noticed he had a lot of aluminum engine blocks and heads in for work}. The owner said he would be able to set up the Jag heads and to bring them in with the cams and valves and such. Said not to buy the shims ahead of time (I mentioned they were readily available but $6-9 apiece): he would measure the thickness of my existing shims, ID those that could be re-used, do the initial set-up, and calculate which shims I should to buy. Then finalize the head set-up. He mentioned a 3-angle valve jobs, inserting hardened valve seats, machining the mating surfaces of the heads and block; I felt good about this part of the discussion

I commented that the tips of the valve stems were not to be machined or trimmed. He replied Yes, they could be. He could remove up to 20 thousandths; after all – the stems were machined at the original factory (I don’t know this to be true). I am not a machinist, and only pretend to be a mechanic, but I recall reading here and elsewhere that Jag valve stems are not to be touched; all adjustments are to be made using only the shims.

QUESTION: So – given the above info, should I:

A) continue to use this machine shop and let him machine the valve stems (I don’t know of another in town but Wiggie undoubtedly knows of a good machine shop in Denver (75 miles north)) (*)

B) it’s OK to trim off up to 20 thousandths - the admonition applies to the 6-cylinder engines; the V12 engine components were made of more modern stuff and can be machined

C) RED FLAG! Run, don’t walk, away from this shop. Go elsewhere

Curious in Colorado – Craig
(*) I am hoping to find/use a local machine shop. If this placed is a no go, maybe Wiggie knows of a competent machinist in Denver. Otherwise I intend to crate to heads and avail myself of Coventry West’s excellent services for the heads

Hi Craig,
Can’t answer your questions but I would encourage you to post it on the V12 section, I think you’ll get more information. I see Kirby Palm and several other experts on the V12 post there.

If it were me I would pack those heads and send them off to Dick Maury at Coventry West. That way you will know they were done RIGHT. Dick rebuilt my 68 E Type engine and it runs so smooth you can set a wine glass on the head.

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+1…Peace of mind has real value.

Just about the valve seats, all Jag valve seats are hardened, that is my personal red flag but it is really small. Some people want and buy this useless information, he might just have wanted to say ‚new valve seats‘.
Maybe the valves can be shortened a little, depending on how deep the hardening goes, but is it good practice? So in theory, yes, something could be shaved to prove a point but I wouldn’t.
Best way to go about the shims is to buy a full set and sell it off to the next one, or take time to reorder them.
Just don’t overtighten that sensor!

Lynn – an excellent recommendation that I just executed.
We’ll see what the V12 gurus over there have say.

David – you can safely bet your last dollar on that point.

Two to my name, and trust me I would!

I’ve moved this to #v12-engine

I don’t know the 12 that well, but I’m not a fan of topping valves - if there are shims then use the appropriate shims, if the shims are too thin, then the seats need replacing (or someone has already topped the valve - then you need a new valve AND a new seat).

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The valve tip is not case-hardened like the old rocker designs so there is no layer to break through. However, done to excess the shim no longer rocks on the tip but sits flat and unmoveable on the spring collar, which risks dropping a valve. Jag valve seats are hardened but not to Stellite or other modern standards, so in theory can be improved. However, seat material expansion and interference fit are critical to avoid dropped seats.

This winter we had a 1750 Alfa engine (very similar to the XK in gen’l arrangement) which was very nice and clean, but down on power. Someone had cut the seats too deep, then they’d topped the valves because the smallest stock shims were too thick. The work looked well done, except the shims were then in contact with the collets on two cyls, so they were getting damaged and on the verge of letting go. As they’d cut the seats far enough back that the Al material of the head was also cut back around the seats the head was scrap (well, not economically viable to weld back up).

This just a few months after an almost identical situation with a 150 S head… except the valves on the XK looked like someone had topped them with an angle grinder.

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