Valve shim dents?

We got the head placed yesterday and I started setting up the cams. I noted that every exhaust shim had a noticeable stem dent in the bottom. It was enough to increase the clearance to .007 on all of them. But none of the intakes had a measurable dent, just small mark.

I assume this can be attributed to the extra pressure on the exhaust ones from opening on the compression stroke? I was able to resolve it on five of them by just flipping it over, so mainly a point of curiosity.

Interesting: I do not recall seeing that kind of pattern, which is not to say it’s not a real thing.

Opening the exhausts to 0.007" ain’t a bad thing: I regularly set them to 0.008".

Those impact indents are normal wear. It is acceptable to turn the shim over to get correct clearance if you are just reseting the clearance.

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yes, are…ok to flip, be sure the shim can rock on the stem, I set mine at the 006-008 spec. I would micrometer verify all shims…at the edge since there is a center dimple. Re install the followers in same locations (unless using new…and if new…mic the thickness) (Cam caps I am sure you know…exact same place and orientation per the little stamped numbers on cap and head., titen down evenly a little at a time across all ) Seems the “rule” is that even tho all metal, all mechanical, all measured and micrometer checked…it always takes twice. It is a fine time to apply a little new cam assembly lube to the cam lobes.

I had these on pretty much all my Mk2 exhaust shims. I milled them - I turned them over as well.

If you mill them and turn them over, how would that bring you back to the original size? Mine had opened up from 6 to 7 because of the dent. I do have to wonder if they’ll last as long flipped over. The pad on the inside of the follower is larger than the dent but not by a whole lot, so it might start denting from the top.

I mainly found it interesting that only the exhaust side had the issue. On the other side several had closed by a thou. I’m now thinking that on the exhaust side the shim takes the beating from the compression stroke and on the intake side the valve seat takes more of a beating because the valve is closed during compression?

I spent a couple hours last night hand sanding 3 intake shims on a flat stone with emery. What a pain in the butt, and now my hands are all cramped. I’m thinking now of getting some kind of arbor turned with a 17mm recess in the end, and a smaller hole inside that one to place a rare earth magnet. That way it could just be chucked up in a drill press and perfectly milled in a few minutes.

Wouldn’t this be easier to just replace with non dented ones?

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They’re like 12 bucks each now plus having to pause work to order them. There isn’t a reason to mill dents unless both sides are dented and you want to restore it for potential future use in a another valve. But if the valve seat gets pounded and you need a thinner shim, then it has to be either milled or replaced.


I guess when I junk my spare engines, I’ll harvest those.

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SNG’s web site shows the one’s they recommend selling for a tad over $7. XKs sell for $3.50.

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If you mill them and turn them over, how would that bring you back to the original size?

I should have reread and been a bit more expansive. Milled some smooth then back into my little stock. Replaced some from stock and turned over the ones that just showed a “shine” in the centre. It’s 0330 here - earlier woken by a call from Pakistan - still dopey as earlier.

Why buy new ones when you can just turn the old ones over as I assume people have done for years.

Indeed, assuming the thickness of the old ones are what you need.

I always reused dented ones.

you can simply turn them over: …as I said, mic all shims…if dimpled, mic away from the center dimple. Be sure they rock on the stem end…if they don’t…the stem may have been round at some point. (a temporary fix in this case is grind off the outside of the shim as needed,…but not the center contact point…)… I “think” (hate to say that) that the shims have a hardened surface…and that sanding them removes that… let alone that in sanding, you would NEVER achieve the smooth shiny hard surface of new shims. I would not do that…for $4 per shim. Small investment for new…yes I know you have to have on hand…many more sizes than you will end up using… Some of us had/have a large set of shims from prior work…that we would send around to whoever was doing a valve adjust…to use/and replace…send back. I have such a set which is quite comprehensive with many multiples. Put new cam lube on the shims…soak em in overnite, …same reason we put on new cams…and related to why we must use ZDDP in engine oil…to help protect flat tappet cams, and a bit similar issue in the shims tho not at all as critical. This IS a good time to put new cam assy lube on the cams.

When I ordered what I hoped I needed but didn’t quite nail it the first time, XKS was good enough to pop a couple of shims in an envelope and just mail them to me.

Of course that was pre-Moss so may not work now.

I’ve seen a lot of dented valve shims over the years - never noticed a pattern - probably more a reflection on me than reality. No idea why some of them dent - wrong material maybe? I’ve had them made in the past. I use drill rod steel in the appropiate diameter and then they are sized on a surface grinder with a magnetic base table being used to hold them. Unfortunately it’s expensive. Can’t imagine how you could hold them strongly enough to mill them.

just buy em or borrow em…jeez…

Terminological inexactitude Terry. Trying to cut a small, through-hard (or case-hardened) round pad doesn’t make sense. Grinding it is.

Ask 100 people about turning down a diamond and some of the men would assume you’d use a lathe. All the women would say you meant refusing a proposal :slight_smile: