I'm replacing the timing chain/rails and tensioner on my 420 and have encountered a problem in taking out the pin for the tensioner arm. The 6mm hex "plug" that covers the pin doesn't want to budge. I first used just a regular allen wrench and it started flexing, so I moved to a hex ratchet and it started to slip, or strip. So I quit turning before I completely stripped it...hoping I could solve this problem before it got bigger. Any suggestions??

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'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."

Here is what has worked for me.

Spray some carb cleaner in the hex on the plug and muck around with a small screwdriver to make sure the fitting is absolutely clean. You need to be able to get as much of the wrench as possible in.

Then spray some PB Blaster around the threads and let it sit an hour, giving it a good tap every once in a while.

Then use a good quaility allen wrench with a perfect end - buy a new one if you have to. Make sure it is inserted perfectly straight. I have found the wrenches get a better "bite" than the sockets. Slip a piece of pipe over it for more leverage. You will feel it flex and then a "pop" as it lets go.

BTW - assume you are removing the tensioner arm to change the lining? On the 116/117, you can change the just the lining and I think you can do it without removing the arm.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I'll go out and try that. How can you get any of that PB Blaster on the inside threads? Can I also use WD 40 for that? Any ideas if I do go ahead and strip it?

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'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."

WD40 won't help. You need the real stuff.

Your options are not great if you strip it. At least on an SL there is no room to get a cold chisel on it. Anything involving a drill or Dremel tool would blow because of the metal shavings.

Maybe others have suggestions, but if it happened in my garage. I would probably end up pulling the head.

I still think if you are taking it out to change the lining, you should look into changing it in place.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe