Head Stud and Nut Torqueing`

["Tom Brown" <tbrown@xxxxxxxxxxx>]

To Summarize:

Nut Torqueing:

Lemme see if I got this right...

On a NEW install of a head gasket or head, the process is to tighten 20 Nm in
the prescribed pattern, then tighten each nut 90 degrees in the same pattern,
then tighten again 90 degrees in the same pattern.   This way all the nuts get
tightened evenly across the head and no distortion or binding occurs because
of the first bolt getting tightened all the way down before the others are
seated properly.

On a RETORQUE, you only loosen on nut at a time.  This procedure is loosen ONE
nut, then tighten to 20 Nm, then tighten a full 180 degrees.   No need to do
two 90 degrees because the other nuts are already seated.   You then go to the
next nut in the pattern, loosen and then retighten the same way.  This is why
there are two procedures in the BMW manuals.   One for retorque, one for head
replacement.  It has nothing to do with the relative accuracy of two 90 degree
turns vs. a 180.

The last item to torque is an allen or star bolt.  It's tightened to, I think,
40 nm...no angle torque required.

- --------------

The Studs:

If the nuts have ever been overtorqued, the studs will be stretched out and
should be replaced.    Once they're stretched out, they'll never work right.
This may be what's happened with the original writer with the oil seepage.

The studs are screwed in to the proper length.  I don't believe thread locker
is specified by BMW for the studs.  The thread fit is Class 1, which is pretty
exact and unsloppy, so if your studs are fitting in loosely, in a way that you
can move the stud around in the hole, they've probably been overtorqued.  No
torque spec is given for the studs, so the length is the determiner, not the
torque.  There is a logic to all this.

Even though listers claim to have had studs creep out on them, I'd bet on BMW
here.   I'm guessing each one of the listers had attempted to tighten their
own head nuts and over done it at least once.

I wouldn't put thread locker in an engine block if none is specified.   You
may not be able to remove the stud!

- -TB