In the MB 615-617 engine manual there is a procedure(05.4) for retightening head bolts. When and why is this supposed to be done, and on which of engines? The implication is that the head gasket may rupture if the head loosens.

I have had 25 MB diesel cars and not yet tightened a head or had one blow its gasket ( while I owned it).

I am fairly certain that most 617 engines have one time use head bolts which can not be retightened, yet there is a procedure for retightening 617 head bolts. So which 617 engines get the procedure?

My 68 220D(615 engine) has 325K miles on it. Is it due for the procedure yet? I am concerned because my friend just blew a head gasket on his 71 220D but he has 360K miles on his.

The last step in the retightening procedure is to adjust the valves as needed, so one must then let the engine cool down at least to 75 degrees C.

While adjusting bolts and valves seems like fun, I won't do it unless it is to have some positive effect on the car. I will appreciete some real wisdom on this subject.

Thank you.

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JMF