Valve Shim Questions

Hi,

About to button up the top end of my engine and decided to measure the valve/cam tolerance on the rebuilt head that I had professional done. I measure .012" up to .015" tolerance on both intake and exhaust sides where the manual calls out for .004 and .006- kinda bummed I have to redo it.

My process was…I properly torqued the cams, measured the gaps, recorded each, disassembled, measured each shim and determined the variation to decided how thick a shim I needed to correct it. When I took things apart I was a little worried when I saw they had grinded the shims and the valve stem ends. I’ve read old forums here that it doesn’t matter if you grind them and others say it does. Which is true? I’ve always thought it was a no no to grind through the surface hardened surface on valves but I don’t know from experience on the XK engine.

My current question is a result of the shop’s work grinding down shims. The grinding process made them wedge shaped- not visible to the naked eye. I determined this by taking a several measurements with the micrometer. I’ve recorded a couple to vary by .003"to .004". This kinda throws off my method of just ordering only what I need because I don’t know how that wedge shaped shim effected my measured tolerances.

I had the work done several years ago (still have the receipt) but just now getting to assembly. Should I ask the shop to fix it if they honor the receipt still or is this acceptable? How loose can the tolerances be? Also, how consistent do the tolerances need to be. I’ve read loose is better than tight…but how loose before you have clicking sounds?

It sounds like I have a lot of assembly, disassembly ahead of me to check the various shim thicknesses if I do it myself.

Thank you,
Ben

First things first. What year and model is you car. Is the engine the original?

In light of the mess the ‘proffesionals’ did I would be inclined to keep well clear of them and be thankful you had the foresight to check prior to buttoning things up.
Are there any Jaguar clubs in your area that you can contact to see if there are mechanics that have a supply of shims that they are willing to loan on a cost per use basis?
Regarding the measurements that you have taken, the shims are only contacting the valve stems in the centre so if you measure there that should give go a starting point for the correct shims.

Sorry, yes 1967, 4.2 and it is original apart from larger pistons on the rebuild.

That’s great information. That will hopefully save a lot of wasted time trying to estimate the correct shim.

They have ruined your shims. The should at least pay for 12 new ones.

It is only a few bucks for a new set though you will be somewhat guessing what thicknesses to order. Once you have a good shim in each you can measure and calculate what you need for the second order.

Hopefully by random chance (luck) or by swapping them around you will only need to order a few more to get things right.

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Yes, the shims are shot. Sounds like a garden variety shop used to working on SBCs and the like–grinding the valve stems is common practice to (approximately) compensate for material removed when grinding the seats. That keeps hydraulic lifters about in the middle of their range.

Sounds like they set it up to later specs used when Jaguar changed to parabolic cams. Assuming yours are not parabolic, they must have changed all of the shims, or, as folks in these type of shops are fond of saying, ground the s**t out of them.

If your cams are four-bolt they are parabolic and the gaps were close. Ditto if two-bolt but with a groove around the circumference of he cam flange. Neither of which overcomes the tapered shims of course.

I hope that there was only one cam at a time in the head if you tested clearances by rotating the cam in question on the bench? Another excellent way to bend valves is to put the head down flat on the bench without allowing for one or two inlet valve heads that will be open and likely projecting beyond the head gasket surface.

Pete

Has anyone ever been successful shimming their tappets in one go?

I’ve been careful not to bend them so far and if I have had to rotate things I’ve loosened the cams so they don’t have any pressure on the valves.

That’s almost the same as my spreadsheet!

I suppose if I am off by .001" looser that isn’t a big deal? I just ordered a bunch of shims last night-we’ll see how it goes.
Out of curiosity how far out do you have to be when you start to notice an issue with tuning or clicking valve train noise? Also, why do hotter engines have a looser tolerance called out in the manual? Is it because they maintain higher revs?

ONE time, in two moves!

I’m running 8 & 10 with the cams that are in my engine and the increase in noise is only apparent with the bonnet open.

Better too loose than too tight. There is an old maxim that says it’s the quiet XK engine you need to worry about.

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measure everything…several times…measure new shims also. May as well measure cam lobe tip to heel just to check, and the cam time position, since your shop work is now "untrusted’. Be sure that when the shims sits on the stem, clear of contact with the ( edit correction, not collet) COLLAR…the shim should “rock” when in place. Then be prepared to do it all once more after you re-install and re-check. It is possible to set the clearances spot on…but even tho all mechanical and measured…a miracle if it is on the first time. NickH

…or, British bikes! :wink:

I had a very, very nice 3.8 head (no corrosion at all around the coolant ports, no rough seats). Went to a “hemi” expert speed shop - valve guides size of old (392?) dodge same as ours, which is an odd size). Nice work EXCEPT he didn’t follow the part about not sinking the valves - maybe he had no choice. Only one was sunk, but it took the thin follower sourced from Jaguar South - if I recall, and some odd shim sizes, but still within those stocked by ‘the usuals’.
I would still be OK with known speed shops if their clients hold records and they do a lot of exotic work, but clearly the best Jaguar specialists would have at least talked to me before ignoring my written cautions.
Since he sized the rods with ARP bolts, I sure hope they weren’t the “bad” bolts that bind on the rod seat. I did measure the sizing, which was on the button, but this was before I knew the ARP problem. I emailed ARP and they sort of owned up to it, but no way of knowing if mine were from the new stock. I know it’s stupid, but I ain’t taking it apart.
The bolts were from Terry’s and I did all the assembly myself - he did handle the skim of the timing cover and otherwise followed all my instructions.

Larry,

Are you saying that ARP produce rod bolts that do NOT have a head with the problem of interfering with the radius on the rod? That’s the first I’ve heard of it, though that doesn’t mean much! All I’ve seen on this forum says that ARP don’t recommend any of their rod bolts for this application, but that if you do use the ones that almost fit, you need to make sure that the head seats properly, and if it doesn’t, remove material until it does. If ARP now have a bolt that is guaranteed to work, I think it would be good to know the part number for future reference.

Unfortunately we only have my 69 year old memory of the correspondence (from maybe 2 years ago). I THOUGHT the response was that they now have specific bolts for this application. My fervent hope is that the interference, which is shown in some old posts in various places, is not a universal problem, but occurs at times. No way the owner would even recall doing my rods, so no joy there. While my car is a '64, the engine is a very early unit (smooth oil pan) and all the original clearances were on spec and the balance of the recip. parts was very good - except the flywheel, which was from Idaho). Maybe (hope?) good, early rods were machined a bit better.
The real “Terry” is long gone from the new ‘Terry’s’, so his competition experience for stocking special parts is, unfortunately, probably not in play.
Part number was: C32344T. For a reason I can’t recall, i got EAC5541TJP connecting rod nuts - 16 of them!! March of 2015