Retightening cylinder head bolts

[jmfitzger]

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.

[P.E.Haiges]

JM,

The head bolt tightening procedure specified in the repair manual is to be used after the head has been R&R for various reasons such as replacing the head gasket, valve job, engine overhaul ETC.

As far as I know it is not a maintenance procedure to be done every so often.

P E H

[leathermang]

" Real Wisdom" ? What forum do you think you are on ?
Each and every one of us think we dispense this with each answer... so you will probably have to weed through the chaff like all the rest of us....
I think for various reasons I would not try it myself.... if you break a bolt due to corrosion having seeped into the threads.... then you have a big job on your hands.... I would play the odds since it has not blown in 35 years on your car....

[Brian Carlton]

If you see a post by a man with a handle:

Leathermang

you will definitely know you are getting some

real wisdom

[Brian Carlton]

Speaking of head gaskets, Greg, what are the odds that I can cure my head gasket leak by tightening the bolts? It's going through about a quart of coolant every 1000 miles now.

I think I already know the answer, but, what the hell, I might as well get some

real wisdom

[leathermang]

You came to the right place...
The relationship of the pull down on something like the head to the friction read on a torque wrench is a very wiggly situation.. approximation is a kind word for it... ( evidence is the 90 degree turn MB requires AFTER reaching the specified torque reading )
One thing which affects it is the quality of the threads on the bolt and the quality of the tap used to make the hole...
Then there is the matter of the Percentage of threads .. most regular quality fasteners are like 75 percent.... some are higher... and this effects the torque reading on the wrench ... which will be higher with 90 percent threads for instance... but will be producing the same amount of pull down on the head. This is due to the greater surface area of the metal in contact with each other in the hole....
Then there is the matter of cleanlyness at the time of putting the engine together... all threads are supposed to be put together " lightly oiled".... trust me on this.... well... trust me on everything.... LOL.... I ALWAYS clean out the hole with the proper tap and then spray out the junk with something like Brake Cleaner... I also wire brush the threads on the bolt... Cleanlyness means everything.
But if you are already leaking the chances of fixing it without taking everything off and starting over CLEAN... is pretty much Zero... and you risk breaking off a bolt or cracking a head trying to do it ....
Sorry about being so ambivalent about this.... when I get my confidance up I will state it more strongly....