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Re: [turbobike] head studs

shammar@nsk-corp.com
Mon, 13 Dec 1999 08:05:48 -0500

That's interesting.  Was that a tensile test for ultimate strength?  How about
stiffness or torsional strength?  It raises an interesting question since the
main function of the stud will be to apply the greatest clamp load possible and
maintain it.  The only way to increase the clamp load is by increasing the
torque on the fastener to further preload it, but a material strong enough to
handle that torque without yielding throughout the operating temperature range
is necessary.  The only way to appreciably increase the stiffness of the stud is
to increase it's x-sectional area (diameter), since Young's modulus is virtually
the same for all steel alloys.  The stock studs on the Kaws are necked down near
the threads to match the thread root diameter.  This may not be the way to go
since multiple threads share the load, but the reduced necked area must support
it.  The aftermarket studs don't have that feature.

Still, it's not totally clear cut and your friend's data is worth considering.
It's funny that often we get sucked into replacing parts, assuming that the
aftermarket parts are going to be better.  It's tough to beat the design,
manufacturing expertise, and quality of material source of a major manufacturer,
and unless the new part is significantly different AND is done properly, it is
often a step backwards.  Pistons, rods, etc. often fall under this category.
Ever have poorly machined pin bores or ring grooves on aftermarket parts?  I
have.  Ever see it on stock stuff?  No.  I've taken a look at a few aftermarket
wrist pins under the microscope and just about shit - they would be cause for
shutting a plant down if we ground something like that.

Buyers beware.

Regards,
Bob






"Lorcan Parnell" <lorcan@mail.globalnet.co.uk> on 12/13/99 07:36:29 AM

To:   Bob Shammas/EQA/Nsk-Corp@Nsk-Corp
cc:
Fax to:
Subject:  Re: [turbobike] head studs



Just as an aside to this a friend of mine who runs a 7-second CBX funnybike
had some aftermarket studs tested and found that they weren't any stronger
than the standard Honda ones (which he had never had any trouble with
anyway).

Regards

Lorcan