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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. |
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#2
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Strange Head Gasket Tightening Sequence
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? |
#3
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Strange Head Gasket Tightening Sequence
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. |
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Strange Head Gasket Tightening Sequence
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 |
#5
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Strange Head Gasket Tightening Sequence
"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. |
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Strange Head Gasket Tightening Sequence
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! |
#7
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Strange Head Gasket Tightening Sequence
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." |
#8
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Strange Head Gasket Tightening Sequence
On Wed, 30 Mar 2011 17:12:31 -0700, Techmann wrote:
> On Mar 30, 12:55 am, Hachiroku ハチ*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! |
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