to retorque or not retorque?
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RKHiPerformance
Turbocharged Sex Cylinder
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Read here:
http://www.turbobuick.com/forums/showthread.php?t=53461
Especially the quote from Alan Rhoerich (6PackToGo).
http://www.turbobuick.com/forums/showthread.php?t=53461
Especially the quote from Alan Rhoerich (6PackToGo).
Thanks for the information and it seems like the thing to do. I did retorque after the motor sat overnight. The header bolts I used are locking style and a real pain to get off while in the car. It seems like there is a possability a stud could loosen but with thick copper headgaskets and the wires imbedded into the copper is there still a chance torque would loosen that much to be of a concern? I guess I am looking for a success story with the same combo I am using to give me a false sense of security.
One thing that has not been mentioned in threads past and present, is the fact that torque wrenches need to be calibrated much more often than most people or shops for that matter do. In my shop I check the wrenches accuracy at the torque I need to use every time. It doesn't help to retorque if you are torqueing to the wrong specification. Danny
One thing I did notice when I retorqued the heads after sitting 24 hours was they did not loosen at all from the intial torquing. They all registered at 85 lbs when I went back over them but I loosend them up and retorqued just to be safe. Of course that was before I ran the motor.
Jerryl
Tall Unvaccinated Chinese Guy
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rtviper said:
Dumb question.
Do you need to loosen up the bolt and than re-torque?
This is what I have always thought but I have been wrong a few times before.
Squid4life
Well-Known Member
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Some guys loosen and retorque each bolt seperately in sequence. That is what was suggested on the 1007's.
Jerryl
Tall Unvaccinated Chinese Guy
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Cool. That is what I did ..... one at a time in sequence!alb84 said:
It got messy following all the links to links to links, but it was pretty clear that some of those who are saying "retorque not needed" were saying that because they have no understanding at all of why retorque is useful.
The GM shop manual will NOT suggest retorque. Why not? Because GM used TTY bolts, and since they are at yield, retorque is not going to gain anything.
With a crushable headgasket, a heat cycle or two can cause the gasket to take a "set", and release some of the preload. As Nick Micale mentioned in one of the links, this will allow some nuts/bolts to be turned more, to get back to the initial preload. Also, especially with bolts, part of the initial torque is used in turning the bolt- the friction between bolt head and washer, and between threads and the block resists turning the bolt, but does not add to preload. After a heat cycle or two, this residual "twist" can relax, loosening the bolt slightly. Not as much of an issue with studs, since the threads in the block don't turn, and there's not much "twist" in a stud when the nut is tightened. Bottom line, retorque is good thing, maybe not absolutely necessary, but useful insurance against a blown head gasket. With some combos, like iron heads with steel shim head gaskets and studs instead of head bolts, the gain won't be very much. With other combos, there will be a bigger gain.
The GM shop manual will NOT suggest retorque. Why not? Because GM used TTY bolts, and since they are at yield, retorque is not going to gain anything.
With a crushable headgasket, a heat cycle or two can cause the gasket to take a "set", and release some of the preload. As Nick Micale mentioned in one of the links, this will allow some nuts/bolts to be turned more, to get back to the initial preload. Also, especially with bolts, part of the initial torque is used in turning the bolt- the friction between bolt head and washer, and between threads and the block resists turning the bolt, but does not add to preload. After a heat cycle or two, this residual "twist" can relax, loosening the bolt slightly. Not as much of an issue with studs, since the threads in the block don't turn, and there's not much "twist" in a stud when the nut is tightened. Bottom line, retorque is good thing, maybe not absolutely necessary, but useful insurance against a blown head gasket. With some combos, like iron heads with steel shim head gaskets and studs instead of head bolts, the gain won't be very much. With other combos, there will be a bigger gain.
Jerryl
Tall Unvaccinated Chinese Guy
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Thanks. I read "most threads" on the re-torque discussions. I used ARP bolts with GM composite gaskets which warranted a re-torque.Ormand said:
During re-torque, I did not see/notice any difference in bolt rotation. While I am certain there was, it is hard to measure accurately with the motor in the car. I did wonder about the torque requirement to with the cured thread sealant and the effectiveness of the sealant after “breaking the seal”.
