Strange Head Gasket Tightening Sequence

I am replacing the head gasket on my '87 Nissan Pulsar. The repair
manual says to first tighten all the bolts to 22 ft. lbs, then go back
and retighten all of them to 50 ft. lbs., then completely loosen all
of them, then tighten all the bolts to 22 ft. lbs, and then retighten
them to a final torque of 50-54 ft. lbs. The question I have is, why
is it necessary to loosen all of the bolts after they are set to the
proper torque only to have to retighten them all over again? Is this
always done after replacing a head gasket? Thank you,
T.C.

On Tue, 29 Mar 2011 19:56:56 -0700, Techmann wrote:

> I am replacing the head gasket on my '87 Nissan Pulsar. The repair manual
> says to first tighten all the bolts to 22 ft. lbs, then go back and
> retighten all of them to 50 ft. lbs., then completely loosen all of them,
> then tighten all the bolts to 22 ft. lbs, and then retighten them to a
> final torque of 50-54 ft. lbs. The question I have is, why is it
> necessary to loosen all of the bolts after they are set to the proper
> torque only to have to retighten them all over again? Is this always done
> after replacing a head gasket? Thank you, T.C.


Interesting. It might be to 'stretch' the bolts so they don't stretch
after tightening the final time.

Pulsar was a cool little car. Did you get the Kammback option?

On 3/29/2011 4:56 PM, Techmann wrote:
> I am replacing the head gasket on my '87 Nissan Pulsar. The repair
> manual says to first tighten all the bolts to 22 ft. lbs, then go back
> and retighten all of them to 50 ft. lbs., then completely loosen all
> of them, then tighten all the bolts to 22 ft. lbs, and then retighten
> them to a final torque of 50-54 ft. lbs. The question I have is, why
> is it necessary to loosen all of the bolts after they are set to the
> proper torque only to have to retighten them all over again? Is this
> always done after replacing a head gasket? Thank you,
> T.C.

My guess is that pre-stretching the bolts makes them slightly more
elastic. You're also pre-flattening the gasket which may make the final
torquing more stable. I'd follow the instructions carefully.

Techmann wrote:
>
> I am replacing the head gasket on my '87 Nissan Pulsar. The repair
> manual says to first tighten all the bolts to 22 ft. lbs, then go back
> and retighten all of them to 50 ft. lbs., then completely loosen all
> of them, then tighten all the bolts to 22 ft. lbs, and then retighten
> them to a final torque of 50-54 ft. lbs. The question I have is, why
> is it necessary to loosen all of the bolts after they are set to the
> proper torque only to have to retighten them all over again? Is this
> always done after replacing a head gasket? Thank you,
> T.C.

I would guess it is due to the composition of the gasket material. The
idea of tightening a head in the correct sequence of steps is to spread
the load on the gasket evenly. They probably discovered experimentally
that doing it twice produced fewer head gasket leaks/blowouts. That
would be because the gasket ends up more densely compressed.

-jim

"Techmann" > wrote in message

Is this
> always done after replacing a head gasket? Thank you,
> T.C.

The answer to this is no. There is more than one way that
manufacturers have specified to torque head bolts. This one
is not a standard method.

On Mar 30, 12:55 am, Hachiroku $B%O%A%m%/(B > wrote:
> On Tue, 29 Mar 2011 19:56:56 -0700, Techmann wrote:
> > I am replacing the head gasket on my '87 Nissan Pulsar. The repair manual
> > says to first tighten all the bolts to 22 ft. lbs, then go back and
> > retighten all of them to 50 ft. lbs., then completely loosen all of them,
> > then tighten all the bolts to 22 ft. lbs, and then retighten them to a
> > final torque of 50-54 ft. lbs. The question I have is, why is it
> > necessary to loosen all of the bolts after they are set to the proper
> > torque only to have to retighten them all over again? Is this always done
> > after replacing a head gasket? Thank you, T.C.
>
> Interesting. It might be to 'stretch' the bolts so they don't stretch
> after tightening the final time.
>
> Pulsar was a cool little car. Did you get the Kammback option?

Thanks for the reply. Well considering the car has 170,000 miles on
it, I probably don't have to worry about "stretching" the bolts since
they have already gone through literally tens of thousands of
expansion/contraction cycles as part of normal driving in the last 24
years we've owned it. However, I will follow the sequence just in
case it has something to do with compressing the head gasket
material. To answer your question, no, it does not have the Kammback
option. With the sharp nose and fold-down lights in the front , the
car is already pretty aerodynamic so not sure how much improvement the
Kammback would offer. It definitely changes the cars look though!

Techmann > wrote:
>Thanks for the reply. Well considering the car has 170,000 miles on
>it, I probably don't have to worry about "stretching" the bolts since
>they have already gone through literally tens of thousands of
>expansion/contraction cycles as part of normal driving in the last 24
>years we've owned it.

I would check the manual and make sure it specifically says you can
re-use the old bolts.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Wed, 30 Mar 2011 17:12:31 -0700, Techmann wrote:

> On Mar 30, 12:55 am, Hachiroku ãƒ�ãƒ�ãƒ*ク > wrote:
>> On Tue, 29 Mar 2011 19:56:56 -0700, Techmann wrote:
>> > I am replacing the head gasket on my '87 Nissan Pulsar. The repair
>> > manual says to first tighten all the bolts to 22 ft. lbs, then go back
>> > and retighten all of them to 50 ft. lbs., then completely loosen all
>> > of them, then tighten all the bolts to 22 ft. lbs, and then retighten
>> > them to a final torque of 50-54 ft. lbs. The question I have is, why
>> > is it necessary to loosen all of the bolts after they are set to the
>> > proper torque only to have to retighten them all over again? Is this
>> > always done after replacing a head gasket? Thank you, T.C.
>>
>> Interesting. It might be to 'stretch' the bolts so they don't stretch
>> after tightening the final time.
>>
>> Pulsar was a cool little car. Did you get the Kammback option?
>
> Thanks for the reply. Well considering the car has 170,000 miles on it, I
> probably don't have to worry about "stretching" the bolts since they have
> already gone through literally tens of thousands of expansion/contraction
> cycles as part of normal driving in the last 24 years we've owned it.
> However, I will follow the sequence just in case it has something to do
> with compressing the head gasket material. To answer your question, no,
> it does not have the Kammback option. With the sharp nose and fold-down
> lights in the front , the car is already pretty aerodynamic so not sure
> how much improvement the Kammback would offer. It definitely changes the
> cars look though!


I wouldn't reuse old bolts, esp with 170,000 miles on them. Get new ones.

And the Kammback was a factory option: you remove the hatch and bolt the
squareback in it's place. Sure wish they made these now! I could use one!