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The VC bolts will be wrong if one follows the factory spec, as the first ones tighened will be loose by the time the other bolts are tight and the rubber gasket gets compressed. So one has to go over all the bolts more than once!
Agree that the breakaway torque of the bolts is a tricky issue. It would detect grossly improperly torqued bolts.
One could mark the bolt heads, then back off, 44 +90 degrees and then see how much the angle of the bolts changed and how that varied from one bolt to the other. That might be the best measure of variability. And if ones that had proper torque to begin with did not show an angle change, then one would know that the bolts were not actually stretching. The torque plus angle is a valid way to torque non-stretch bolts as it actually removes some of the friction errors from the resultant state of bolt tension.
I have an electronic torque meter, still a virgin, that I want to use to measure peak breakway torque and the peak torque achieved at 90 degrees. Then we could use that peak 90 torque as a torque wrench setting to to check for loose bolts instead of 44. That would not be used for tighening for several reasons, but would be better than 44 to check for ones that are loose! The static breakway friction still is a large factor. To tighen, one will still want to do the spec procedure.
When some bolts are found to not be tight, these need to be taking a load when the bolts nearby are tighened. So these looser bolts need to be discovered and put to work before doing the complete torque pattern. But one also does not want to re-torque stretch bolts needlessly.
And as stated by ARP, as a bolt is retighened a few times, the bolts and tapped thread are burnished and the friction of the threads is reduced. For their non-stretch bolts, they want one one perform that operation several times to condtion the treads then tighten to final torque. And when studs are used, threads on the upper end are a fine pitch and the engagement length is short and a known quantity.
With a stretch bolt, forces are limited by the bolt yielding. So with the first few engine heat cycles, the expansion of the head may make the bolt yield and that means that the forces of the bolt on the aluminum head are limited. With a high strength bolt, it is possible to damage the aluminum head with excessive bolt forces. The bolts in the Saabs are quite heavy, thicker than most in other engines, and the same as some heavy diesel engines. So these bolts are relatively stiff, as not been very elastic, and this does increase the concern for crushing the head with not-stretch bolts. When using non-stretch bolts, there are many issues that need to be addressed to arrive at a proper torque for an alloy head. For cast iron heads, one does not have the difference in expansion of the head VS the steel of the bolts to worry about, and the heads would tolerate higher loads in any case. A stretch bolt does have some advantages. But bolt strength consistancy is vital. That is not only a factor of how the bolt is alloyed, but also its time, temperature and deformation history.
, Sat, 5 Feb 2005 19:12:05, Sat, 5 Feb 2005 14:48:32, Sat, 5 Feb 2005 15:20:43, Sat, 5 Feb 2005 15:36:05
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