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Stripped valve locking nut 1983 300D - Now what???

Submitted by NSA on 6 May 2008 - 9:18am.
Hi all; Was doing my first valve adjustment and am convinced that the #6 valve has a stripped lock nut. I'm concerned that the valve stem itself is stripped, but when I tighten down the top (adjusting) nut, the locking nut just glides with it, and I CAN get a ton of clearance for the rocker arm. What's involved in changing the locking nuts? Do you have to remove the cam, etc? I know that either (or both) the threaded valve stem or the nuts can strip. Typically, does the nut give out first? Hoping to hear that I don't need to pull the cylinder head. Any advice would be highly appreciated. Things seemed to be going smooth until I got to that one. Is this common? NSA - Hazleton, Pennsylvania
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Suspect the bottom nut

6 May 2008 - 2:04pm
Kent Bergsma

I have seen this happen quite a few times. The lower nut is specifically a softer metal that either the valve stem or the top nut - so in my experience it is always the one that strips and does not cause damage to the vavle stem threads.

On the other hand replacing it is rather involved, but you don't need to remove the head or the cam. Since you are going to change that nut I would recommend you plan to change your valve stem seals while you are at it. You will already be half way there. My valve stem seal replacement kits comes with extra nuts and gives complete illustrated instructions on how to do do it. Kent

more info...

6 May 2008 - 2:34pm
NSA
Couldn't resist it. I already did some rapid internet perusing and found that you take the rocker arm off to get to the nuts, etc, and proceeded. It WAS the lower nut, just as you suspected. Whew! I am glad to see that you have that kit, and it makes sense to do the valve stem seals now. One minor, I hope, complication is that I made a mistake that I hope isn't a big deal, but I'd like to confirm that blunder. You see, I set the marks on the engine to TDC, I thought, but realized when I had the spring off the problem valve, that I was out of synch. The valve can drop into the cylinder. (I put the top nut back on, so it didn't drop in...) Since the rear rocker arm has been removed, am I correct to assume that as long as an assistant kept that valve held all the way closed, that I can rotate the engine 360 degrees and get to the proper "TDC", where the valve wouldn't be able to drop in as it'll be blocked by the piston? To remove the rocker assembly, all I did was remove the 3 fasteners and slid it out. The car sits, with that rear triple rocker assembly removed and the messed up valve hanging in place via the adjusting nut. Is there something that I should know about getting it back together? Thanks for the quick response. Glad it's not, I think, as bad as I feared it may be. Hope I didn't do something really dumb in what I've described. : ) Anyway, am I correct regarding rotating the engine clockwise another 360 degrees to bring the piston into the correct position? A little knowledge can be a dangerous thing, I know, and although I think that no permanent or complex harm was done, I'd sure appreciate confirmation. All the best... NSA - Hazleton, Pennsylvania