Re: Awesome Response! Very Comprehensive, Thanks! (n/m) - Saab Performance Bulletin Board - Saabnet.com
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Re: Awesome Response! Very Comprehensive, Thanks! (n/m)
Posted by 2Slow (more from 2Slow) on Wed, 23 Jan 2002 18:30:59
In Reply to: Awesome Response! Very Comprehensive, Thanks! (n/m), Kyle, Wed, 23 Jan 2002 15:20:03
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If the torque spec for the head you are using is similar to the one that chrisx states (where there is both a torque spec, than a dimensional spec +90º for example) the fastener is most likely designed to yield. If the torque spec is simply a torque sequence, it most likely does not yield the bolt.
When the bolt starts to yield the torque at the wrench will vary and probably go down slightly. It would be very difficult to specify a torque at which the bolt will yield, so they simply specify a torque and than tell you to take an additional dimensional spec. (a quarter turn for example)
The problem with re-using the bolts is that thy can only be yielded so much/many times before failure. Like I said before, I have reused head bolts on many vehicles. I am very careful and actually will stop turning if I feel the bolt yielding a lot on the final torque down, rather than hit the dimensional spec of x degrees of turn. Once the bolt is yielding, I maxed out the preload anyway.
I am not advising re-use of head bolts. For the pidly cost it probably is wiser to replace them if they are the type that is designed to yield. (Do as I say, not as I do)
If you do decide to reuse the bolts, I would also look for any visable signs of necking where the cross section of the bolt is actually reduced. If necking is visable to the naked eye, the bolt should not be reused. Even if necking isn't there I would definately not use head bolts that are designed to yield more than twice. After that you are playing with fire.
-Joe
posted by 198.208....
Posts in this Thread:
- New head bolts...necessary?, Kyle, Wed, 23 Jan 2002 12:13:40
- Used old ones 250k all ok on 900 turbo w/ac in Tx!(n/m), gtw, Wed, 23 Jan 2002 17:44:32
- Re: New head bolts...necessary?, chrisx, Wed, 23 Jan 2002 14:23:26
- BTW: Two different dealers + one independant..., Kyle, Wed, 23 Jan 2002 13:24:03
- Re: New head bolts...necessary?, Shaun
, Wed, 23 Jan 2002 12:53:11 - You're supposed to, but I never do., Jeff Cunningham, Wed, 23 Jan 2002 12:23:07
- Re: New head bolts...necessary?, Simon S, Wed, 23 Jan 2002 12:18:21
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