I have always had the notion, especially with diesels, that a " loose valve is a happy valve"...meaning that when adjusting valve clearances, especially on a high mileage engine, that adjusting the clearances to a gap that is a little wider than spec. is a good idea. This is also based on a notion that if the valves are a little loose, they may "bang themselves in" a little better, closing the clearance gap a little, but still leaving enough clearance so as to ensure that the valve fully closes. I also think that if the valve clearances are a little wider than spec. would result in a little more clatter, but this is hardly an important factor with these old Mercedes 123 diesels.

1) My question is: Am I making a mistake a adjusting cold valve clearances to .15 (intake) and .40 (exhaust), instead of .1 and .35? What is the downside from doing this.


2) my second question is related to something someone said in another string...he mention that when you adjust valve clearances, to rotate the valve and set the clearance when the valve is at the tightest point. I never even thought of doing this, and it sounds like a good thing to do. Do you folks rotate your valves when setting valve clearances?

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

1) Yes, you are making a mistake. Setting them "loose" means that you're at .11 instead of .10 on the intake and at .36 instead of .35 on the exhaust. Anything more and they'll start to rattle and cause significantly increased wear on the tip of the stem.

2) Never did it. Don't see the necessity.