Stretch bolts?

[vwscir88@hotmail.com (the hitman)]

i've known this for awhile, my buddies mike(certified porsche mech)and 
steve(certified vw mech.) told me this when we did the head on my first 16v. 
we reused those headbolts and i never had one problem. in fact i have a box 
of headbolts that i keep around as spares from vw's that i have parted out.
  brett


>From: "Larry" <rocco16v@netzero.com>
>Reply-To: "Larry" <rocco16v@netzero.com>
>To: <scirocco-l@scirocco.org>
>Subject: Stretch bolts?
>Date: Sat, 18 May 2002 17:50:36 -0700
>
>Read a very interesting article on fastening in the May issue of ASSEMBLY
>magazine. (we get some pretty esoteric journals at work....) This article
>focused on selecting the best tightening system for a bolted joint.  Here's
>what I found:
>
>Guess what.... neither our head bolts, rod bolts, nor pressure plate bolts
>are 'stretch bolts'.
>
>Our bolts use a method called "angle-controlled" tightening.  The benefit 
>of
>this method (apply low torque value, then apply a prescribed, additional
>turn of a precise angle) is that it is not affected by friction....dry
>threads, dry head, oiled threads and/or head and/or washers, etc. do not
>introduce clamping force variables.  This is probably why VW used this
>method; the head may be oiled or not, the bolts may be clean or oiled, etc.
>This method does NOT elongate the bolt past its yield point (permanent
>deformation or 'stretch')
>  In contrast, the strategy of tightening to the yield (stretch) point is
>done by monitoring the rate of change of torque over fixed angle 
>increments.
>This is by far the most consistant way of torqueing a bolt, but requires
>very sophisticated, expensive instrumentation, typically costing in the 
>$15K
>range for a tool capable of the torque required by our head bolts.
>
>Bottom line:  despite what we have believed for all these years, VW does 
>not
>use "stretch bolts" in our engines.
>In fact, I could not find any warnings in my Bentley about re-using those
>bolts.
>They can be re-used.
>Any thoughts? comments?
>
>Larry  sandiego16V
>
>
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