S54 Valve Adjustment - 3.0mm shim?!

[m090030]

Bottom line: I have a 3.0mm shim on one of my S54's exhaust valves - is this an indicator of a problem? I need it to be ~2.93mm to get the right clearance - any idea how to achieve this?

More details: I purchased a 2001 M Roadster in pretty rough shape recently, and it has a pretty bad engine knocking sound. Based on some research, I think it's either some damaged valvetrain components, VANOS, or a rod bearing. I started off with a valve adjustment. 6 valves were out of spec, but none too bad. Most were correctable, but one of them (Exhaust valve #10) had a very custom-made-looking shim that was 3.0mm thick! The normal kit of shims only goes up to 2.6mm. So ... is this alone an indicator that I need to dig further into the valvetrain? Or should I pursue getting a custom shim made, or grinding 0.07mm off of the current shim, and see how it goes? The car has 220,000 miles, but this seems like a very out-of-whack thing.

I've attached some pictures below - I can't see anything wrong with the cam, rocker arm, or valve, but I don't have a very well trained eye for this level of stuff.

Thanks in advance!


IMG_20171201_080145114.jpgIMG_20171201_080157970.jpgIMG_20171201_080520489.jpgIMG_20171201_080206051.jpgIMG_20171201_080214928.jpg

[Randy Forbes]

That's a little thicker shim than I can recall using__just checked the worksheet from Rando's S-54, and the thickest shim I used on it was a 2.24mm. I know that I've NEVER used any of the 1/3 thinnest or thickest shims in the assortment kit's range, always being able to find the right size among the middle third of the range.

Unless I'm not understanding it right, a recessed valve seat would require a thinner than average shim to get the right clearance. If the stem's tip and or cam follower was degrading, then a thicker shim will be required. I think...

[m090030]

Thanks for the reply - Yeah, this is waaaaay outside the normal range of the standard shim set. Someone suggested a worn rocket arm/follower, which would make sense. The previous owner treated this thing like a Honda Civic (crap 5w30 oil, never a recorded valve adjustment, etc), so I wouldn't be too surprised at some wear here.