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Yes, mine is a 985 engine too.

Anyone know whey the guides in these cars get loose? Does the guide wear or is it the head?
Yes sorry, I typed 982 because that is what our earlier models have. But 985 didn't show up either for that 116 050 4724 part number.

Hmm, don't know what this means, could it be multiple tolerances with one part number?
Could it be that the diameters are not uniform along the length - tapered or stepped diameters??

In looking for a picture of the guide, I went to Autohaus Arizona (usually reliable). They also say that the 4724 part number doesn't fit a 1980 450SL ????? Maybe check with a Mercedes dealer along with engine number to be sure!
 

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Found this company who appear to be a manufacturer of valve guides for OE markets.

Interesting description of how the valve stem heat is dissipated. Just thinking that having a layer of Loctite or similar may affect the heat transfer from the stems through the guides to the head.


How do guides become loose? Maybe if valve stems lose lubrication, they bind and cause some movement of the guides? Who knows, but interesting that MB originally had three sizes for our cars.
 

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Yes, certainly less severe service on inlet. But there is still frictional heat to dissipate. The copper-zinc alloy that MB uses likely transfers heat better than cast iron does.

By the way, are the guides made to an exact fit? Or do they need honing or other machining during installation? It's been a long time, but I seem to recall something about that. Also first freezing guides before installing. Maybe have a good MB shop rebuild the head?

Anyway, good luck with it.
 

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Discussion Starter #29
Thanks for that, I am now also understanding that there is also a slightly over sized version of the original part.

A 116 050 36 24 . VALVE GUIDE. INTAKE,REPAIR SIZE I. [007] 14.043-050 MM

and I have also found the dimensions for the A 116 050 4724 which is also 14.043mm, so this is equivalent to the first repair size as above.

I also found the dimensions fro the 3624 and the 4724 in the specs for the TRW equivalent parts.

1160503624 ---> TRW 81-2685 ----> 14.035mm
1160504724 ---> TRW 81-26118 ---> 14.043mm
 
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