Bill Babcock wrote:
> I've got billet pedestals and ARP bolts, haven't had a problem. Make sure
> that your bolts bottom out though--it's easy to have them only threaded in
> part way. Same for head bolts. I use a good stud extractor and lean on
> them after cleaning the hole.
Ding, ding, ding....
Wrong. If the bolt bottoms out and is torqued further, the bolt is in
compression, not tension. This actually _reduces_
the tensile load, because the compressive load is subtracted from the tensile
load. Increasing the thread engagement is
okay (although there's some evidence that only the first few threads carry the
total load), but bottoming and torquing
against that bottoming works the opposite of what is required of the bolt.
Tensile loading of the bolt is actually
reduced by doing so. If you want to test that theory, do it with the stock
hardware which has a far smaller margin of
safety, rather than the ARP hardware.
Proved in practice. Our idiot engineers spec'd a bolt for securing a cradle
mount to a ZF trans which bottomed out in
the mounting holes of the trans adapter. Broke `em all, at considerable expense
for fixes in the field.
It's just geometry. If the bottom of the bolt is forced against the bottom of
the thread bore, which side of the bore
thread does it engage? The lower side, because of compression. As the bolt is
tightened further, it's simultaneously
being loaded in compression and tension. Clamping force is therefore reduced by
the amount of the compressive load.
Always ensure a bit of space between the bottom of the bolt and the bottom of
the bolt boss.
Cheers.
--
Michael D. Porter
Roswell, NM
[mailto:mporter@zianet.com]
Never let anyone drive you crazy when you know it's within walking distance.
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