Haynes manual says to tork head bolts to 37 lb then turn 95 degrees
in the order noted. Results seems to be inconsitant torque on the head
bolts. Some bolts seem to be looser than others if I do this,
especially the bolts on the ends of the head. Is there a problem if I
torque all bolts at the same value with a good torque wrench?

I have not seen this spec. to turn a number of degrees after setting a
low torque value before. ( I have rebuilt lots of older motors) What
gives here?

DW

Further study on the problem has me feeling Haynes Repair manual for
the Malibu 1997 through 2003 may be in error suggesting you reuse the
existing head bolts. There is nothing noted about the head bolts being
torque yield bolts. These head bolts as it turns out are torque to
yield bolts and the Chevy parts guys and mechanics I have been able
to talk to, suggest that that is the source of my problem and I need
to use new bolts. There is some feeling some are using them over once
and only once, but the mechanics I have talked to are not doing any
thing but replace the bolts and do not wish to risk using them over.
There are some finding broken head bolts comming into the shop from
time to time suggesting there is a stretch life on the bolts but no
one was sure about that. It just may be there is a failure rate with
these bolts due to what they are. Due to inconsistant Torqing as noted
in my question, I am putting new Tork to yield bolts on

"DW" wrote

This is another follow up on the replacement of head gaskets on the
2001 Malibu. I got the new torque to yield bolts from a Chevy Dealer.
I found that the complete top end gasket set from Federal Mogul,
does not include a note about the need to use new Torque to Yield
Bolts. Interestingly enough, when you purchase their head gasket only
set, there is a warning noted on the packaging of this set about head
bolts. The note further explains that you need to reference a master
catalog for further info. The independent dealers do have access to
the Torque to Yield Bolts for some savings in pricing above what the
dealers are generally willing to offer.

I removed all of the reused head bolts. (this is after the first
attempt in following the procedures listed by Haynes Repair Manual) I
chose not to reuse the head gasket over, but instead considered the
gaskets damaged by trying to use the original head bolts over again.
After setting a new head gasket, and installing the new Torque to
Yield head bolts, I could clearly feel the difference. The consistency
of pressures needed to turn the wrench the 95 degrees, following the
Torque of the bolts to 37 lb., was very clearly evident.

I hope this experience will help some one out in the future.

D

"DW" wrote

"DW" <none (AT) 000 (DOT) com> wrote

I found this procedure strange at first, also. If you study it, you will
find that it was developed because torquing with a torque wrench does not
give predictable or uniform pressures on the head to the same degree of
accuracy. The whole purpose of tightening a bolt is to elastically stretch
the bolt and thereby apply (and maintain) pressure on the joint. By
controlling the stretch (yield) of the bolt you can get and maintain a known
pressure pretty consistently.

My first exposure to this principle was on 50's Triumph motorcycles where
you used a micrometer to measure the stretch of the connecting rod bolts to
determine the proper tightness.

Don Young