Stripped Valve Nut 1981 300SD / OM617
 

This thread refers.

1981 300SD / OM617

I'm pretty sure that the lock nut is stripped. Heavens help me if the valve stem is the problem. The car's a beauty, so I'm committed to getting the motor back in running order. It seems that the rocker arms need to come off cylinders 3-5 to give me clearance to pull the nuts.

I've never done anything this involved before, but it doesn't seem beyond my capability; has anyone done this/have any tips? I also am looking for the torque specification for the rocker bolts, and what the right part is for the nuts (I'll replace them both while they're off). Can't seem to find them on fastlane...

Any help is GREATLY appreciated.

pretty easy. Make sure you bring that cylinder up to TDC first so you don't accidentally drop the valve into the cylinder.

The nut is W0133-1643198. Probably another part numbering style as well but that's what I found it under. I bought several for when I was putting new valve seals in a used head.

Rocker arm bracket to head is 38nm

Thanks, Chief!

Seems like I'm not the only one to have this problem, although his valve woudn't open up enough; the exact opposite.

So it looks like to remove the rocker towers:

-Rotate the camshaft to put the least stress on the rear six valves

-Unbolt the hex plugs, remove the rockers with a little bit of force

-Rotate the crank/cam to TDC for No. 3 piston

-Remove/Replace the bad nut

-Rotate the crank/cam back to where it was for rocker removal

-Reinstall rockers, torque hex plugs to 38 n-m

Any recommendations for thread lube for the rocker tower hex plugs? 15W-40 and regular anti-sieze both come to mind. Should I get the FSM for this one?

I think I'll rotate the camshaft 360 just to see if that frees up a thread, but this doesn't seem impossible. The 30mm Hazet wrench seems like a necessity for this one to compress the valve spring during installation.

Valve Lock Nut 1539900251 (Mercedes Part Number minus the "A" at the Front of the Number that is normally not used).

Fingers can probably do it, although the 30mm wrench makes a nice bit of leverage. I did mine with fingers since I'm now in the paranoid club when it comes to valve guides :).

fsm doesn't mention oil on the bolts or anti-sieze. I used a very light amount of my engine oil (rotella 15-40).

When the crank is in the correct position, you can get that set in and out pretty easily.

Hint....if you're not sure that you've got TDC, as you get the locking nut almost all the way off, reach in between the valve spring with thin needle nose and grab the valve. Take off the nut nut and spring retaining cap, then put the nut back on. Release the needle nose. The valve should only drop down a little bit and rest on the piston face. If not, the nut you put back on will keep it from dropping into the cylinder and ruining your weekend.

Thanks to everyone for the help! I'll take pictures as I do it to add to the DIY bank. My fingers are crossed that I'm not going to be adding one for head R/R, but if I can get the adjusting nut all the way down to where the lock nut's stuck, that suggests it's the lock nut...

I'll use 15-40, and carefully wirebrush the threads before I put the rocker towers back on. 38nm is a lot of torque for those little hex screws!

Good luck! I just did the cylinder head r/r, due to broken valve stem. If'n you're old and feeble it's a heck of a job to do, even with a shop crane I was hurtin a lot.

Valve steel appears to be much higher grade than the nuts, so I'd bet on a stripped nut.

Lower Valve Adjustment Lock Nut 1539900251 (W0133-1643198, westpack number)

Upper (Acorn/Cap Nut) Valve Adjustment Nut 615 053 00 72 (6150530072)

So a week and a half later, the parts and the free time to do the work have materialized, and I'm immediately confounded:

I've unbolted the set of rocker arm towers (set of three for cylinders nos. 3, 4, and 5) and they appear to be very firmly set in place, despite barring the engine all the way around and checking for the optimal position. The loosest place I can find (visually) is with the No. 3 cylinder exhaust valve at 12:00, and it seems that this is the right place, but is there a trick to getting them out that I'm missing? The only bolts I've removed are the three hex-heads on the rocker towers; the XZN ones at the bases appear to be head bolts and not related to the rockers at all.

I don't recall having any special problems when I removed all of mine for the Valve Seal Change.
But, you are not going to find a place where there is no spring Tension pushing on the Arms.

You might look up some of the Valve Seal change threads and see what they did.

What I cannot remember is if the Head or the Rocker Arm Towers (the partst that the Bolts go through to the Cylinder Head) have any sort of Tubes that center them on the Holes in the Heads.
If they do you just need to gently pry up on something to lift them a bove the lip of the Tubes.
If they do you just need to pull up the Rocker Arm Tower

There is some pressure, but not a lot, I was able to (gently) pry mine back toward the passenger side fender. I believe I used a long 3/8 extension socket bar but it took very little force, just slowly applied pressure and they pushed on out.

Hmm... So far my attempts to move the rocker towers (up, out from the camshaft, and a combination) has been moving the engine on its mounts with no perceptible movement from the rockers.

Eric, when you said you pried them out, did you have to move them up at all, or just towards the passenger side of the car/away from the camshaft? I imagine getting them back in was equally tough... I think adjusting all the valves for the rearmost three cylinders for maximum clearance may be in order to facilitate this. Thoughts?

Success! I removed the air cleaner and used a large flathead screwdriver under the rearmost (No. 5 cylinder rocker tower) braced against the intake manifold and it pried off with just a little force.

Now on to the offending nut.

Man verses Machine. Man 1- Machine Zero.

With one stripped nut indicating some pretty rancid wrenching before, have you considered replacing all the nuts ?