After checking the factory manual it is easy to see that when you adjust the valves on a MB diesel you do indeed change the compression on the spring, but it is already compressed quite a bit when you install the valve spring cap, so adjusting the valves will change the springs compression very little. Probably so nil as to be impossible to measure.
If you have the shop manual for the 615,616and 617.91 engines a picture of the valve and spring assembly is on page 05.4-250/5.
Bill Lewallen

Bill,

Thanks for the research. I just didn't remember, I thought the cap that actually contacts the cam follower was a nut and then it was a locknut below. But I didn't remember.

And you're right, I can't imagine this amount of spring change, would make a significant difference during the life of the engine.

Have a great day,

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Larry Bible
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles