I (okay, WE) have a '90 300 SEL with 215k miles - but we bought it a few years ago at about 170k miles. So far, it has been extremely reliable. It's time for a couple of repairs and I'd appreciate help on one of them.

Very noisy lifter. I haven't found the specific culprit, but it seems to be just one. I've already ordered two new ones. As usual, the CD is worthless. I know it can be done without removing the camshaft or anything much beyond removal of the valve cover. Can someone give a few pointers about turning the rocker, or removing it, or exactly what's involved?

Yeah, remove the valve cover first, check the rockers to see if you can find the bad one. One thing to pay attention to is there are small cup-shaped spacers on top of each valve stem where the rocker contacts it. I have on a couple occasions seen this thing flip out of there, possibly due to mechanical "inattention" when reassembling the engine (say for valve stem seals). If they're all there, what you need to do is take a hammer and push down on each rocker to see if you can get one to go down (hydraulic leak down) (OH! push down with the HANDLE of the hammer on the rocker, not the head!). You may need to use a few different engine positions to find it.
If you can find it, the easiest thing to do (but slightly risky) is to just unbolt the rocker assembly that needs the change (remove the sheetmetal oiler tube first, then the 4 bolts on the rocker "bracket" on the cylinder in need of repair, remove the 4 bolts gradually, a couple turns at a time), pull out the "lifter" (it's actually called the hydraulic compensator on an overhead cam engine), put a little motor oil in the new one, and reinstall it. I say "risky" because you should really measure things, but requires a special tool and the likelyhood of anything needing adjustment is slim. The adjustments, in case you want to know, can be done in 2 places: The cup-shaped spacers are available in 2 thicknesses, and also in the rocker arm where the compensator goes in is a shim (it's the part you can see on top of the rocker, usually with a "dot" in the center. That's NOT a hole, it's an ID dot that designates the thickness of the shim). I think there are 4 different thicknesses available; no dot (thinnest)
one dot (most common), 2 dots, 3 dots (thickest). BTW to remove the old compensator usually it'll pull out from below easy, otherwise you can force it out from above with a rap on the top of the shim, BUT reinstall the shim!
Gilly

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Thanks Gilly for the excellent information and detail. I can usually figure this stuff out, but it really helps to know how things are supposed to work before tearing into them.

How do you know that it's a lifter?

Make sure that it's not the belt tensioner shock with a bad bushing first. That can sound very much like a lifter problem.

Also, a $10 mechanics stethoscope can be worth much more than $10.

Reasons I think it's lifter:

Responds to oil changes and different oil viscosities
Comes and goes while idling, and is generally gone at higher rpm's
Sounds like a lifter
Sounds like it's closer to firewall than front of engine
Tensioner/chain renewed at 160k miles

I'm assuming the shock is at the front of the engine. Would it go away with revs or oil pressure?

Thanks.

The shock is up front. If you know where the BELT tensioner is (serpentine belt) this shock bolts to that, you can see the upper half of it, kind of a beeyatch to change. The bushings wear out on the little shock and make a rattling noise.
Gilly

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Here is what I do know:

The 3.0 L inline six indeed is an overhead cam engine. However, the valves and lifters are easily accessible with the valve cover off. You don't even have to fool with the camshaft - simply work on the corresponding arm/lifter.

Looks like you have a V6 or V8? Apparently, the cams are a different setup.

As far as a stethoscope, I usually get by with either a long stemmed funnel or a screwdriver.

Nope, cams are coming off to work on the 5 liter (M119) engine, it's a bucket sort of arrangement. The M103 inline 6 has like a cam-follower arm that rubs against the cam and act like a rocker arm to push down the valve. Technically I don't thing "rocker arm" is the correct term, I think it's called a cam follower, but certainly it's commonly referred to as a rocker arm and I certainly knew what he meant. I't s anice set-up, each cylinder has a pair of rocker arms and each set can be removed with only 4 bolts.
On the M119, the valves are pushed down directly by the cam, I believe there are hydraulic compensators under the bucket, which is what the cam pushes down on.
It is funny that I have no problem with calling the M103 "cam followers" "rocker arms", but "lifter" makes no sense, I call them the "hydraulic compensators". Rockers rock, but in this case the lifters don't "lift", they "push". Hmmmmmm
Gilly

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