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Re: Head Bolts (archive)
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Posted by Jim Baron on May 17, 2000 at 12:09:32:

In Reply to: Head Bolts posted by Bart on May 16, 2000 at 20:25:31:

: I'm told its wise not to reuse head bolts because they stretch or something. I'm not buying it. All bolts stretch, thats sorta how bolts work with torque and tension and such. Are we talking fatigue here? Any enlightenment is appreciated. (This is relating to replacing the head gasket on my 82' 320i).

I've reused hundreds of headbolts on older cars, but starting around 1980 a lot of manufacturers, foreign and domestic, began to do some higher tech engineering to take advantage of that "all bolts stretch" factor to gain more uniform torquing, so I would say that nowadays it's taking a chance unless you know the model of car you're working on and its history of head gasket reliability. I'd surely not attempt to reuse any of those bolts of the type which had a built-in longer extension which was designed to twist off when the robot assembly machine reached what was supposedly the right torque, and I'd be pretty leary of doing it with any of the Mercedes and Porsche late models which achieve final torque by a certain number of degrees of turning after an initial low torque setting.

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