Head bolts 88 735i retorque

["David A. Leonard" <dleonar1@xxxxxxxxxxxx>]

Having done the cylinder head twice..once at 141k miles to replace a cam,
and once at 224 to fix the blown head gasket, i've played with head bolts on
these motors a little. I consulted with my dealer mechanic friend, who has
done a lot of these heads.

While the factory has recommended a two step torqueing procedure, they have
changed it around a few times, as the results were spotty.  The latest is
the one Chris referred to.. tighten to a torque value, run 25 minutes, then
angle torque.  My buddy at the dealer , being a flat rate guy, showed me an
older procedure using a just torque it to 70 lbs and run it. This is what he
uses, and you know those flat rate boys don't do anything that results in a
"comeback" if they can avoid it!

I followed the factory "run then angle torque" procedure the first time, and
experienced an 80k head gasket failure between Cyl. 5 and 6.

When I brought the head by Victor, at the dealer..beep the horn, drive the
Suburban in...show it to him, (got a really accomodating dealer here in
Maine), he commented that that was where they all failed.

On the latest head, I just used the torque to 70 ft. lbs and run it
procedure..BUT.. I didn't get the valves tight enough, and needed to take
the valve cover off to reset them a couple of hundred miles later.

Being me, and never being able to leave well enough alone, I grabbed my new
click type torque wrench and backed all the bolts off 1/4 turn, one at a
time, in the book torqueing sequence, and then retorqued each one
immediately to about 80 ft lbs, on each one.  You need to loosen, as torque
wrenches onle measure accurately when moving.  I like doing them one at a
time as you don't want to "uncrush" the head gasket..leaving all the other
bolts tight keeps this from happening.

Here is where it gets interesting:  All of the bolts, except the ones on the
number 6 cylinder end, took about a little more than the 1/4 turn I had
loosend them to reach 80 ft lb.s , the pair on the # 6 end took a little
more than 1/2 turn to reach the same value..When I reported this to Vic, he
thought we may have figured out why "most of them" fail between # 5 an # 6..
Something to do with the design of the head or the gasket must be causing
that end of things to loosen up in service.  You can see that the angle
torque procedure , which is consistent on all the bolts won't address this
problem.

Dan Patzer (A BMW CCA tech club guy) once recommended to me retorquing all
BMW head bolts this way: "Using a beam type wrench, attempt to tighten the
head bolts to 65 ft. lbs, if they start to move keep turning 'till you reach
80 ft lbs." (hope I remembered this right Dan)


As far as I can tell, you can't go too far wrong retorquing.
YMMV

Dave Leonard
88 735i
91 325iC Leave the top down and use it like a bike!

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