Yes, Mike, we did knock around the question for a while, and we DID come to
conclusions, only not the same ones!
First, the credentials: although I am no longer a practicing, slide-rule
wielding structural engineer, that was my origin in the military aircraft
world.
>From a structural analysis point of view, the bearing/spacer/bearing stack
adds no strength to the stub axle because it is not structurally connected to
(bolted, welded, or an integral part of) the stub axle, and consequently
cannot resist either bending or shear loads applied to the axle by the wheel.
Bending loads are the maximum at the root of the axle (that's why cracks
appear here first), and the spacer stack merely "sits" here. It is not
attached, no matter how much it is compressed against the butt of the axle by
the axle nut.
There seems to be very little actual technical information available on
exactly why the spacer and shims are used in the Healey application. However,
bearing engineering books indicate that ball bearings have inherent axial
freeplay between the inner and outer races. In order to eliminate this
freeplay, which could cause some lost motion in steering (my assessment), the
spacer and shims are used to pre-load the bearings and remove the freeplay.
This arrangement may not be necessary for tapered roller bearings, which have
less inherent freeplay.
I can't remember whether my BJ8 has ball bearings or tapered rollers, but I
used the spacer and the shims, and I set up the wheels according to the
manual. I believe they are necessary for ball bearings and couldn't hurt for
rollers.
To have your Healey opinions respected by Mike Salter is quite an honor.
Thank you, Mike!
Steve Byers
HBJ8L/36666
BJ8 Registry
Havelock, NC USA
----- Original Message -----
From: Michael Salter
To: 'Dave & Marlene' ; 'Bob Spidell'
Cc: 'Austin Healey'
Sent: Wednesday, May 26, 2004 7:07 PM
Subject: RE: Front wheel bearings
This is a question that Steve Byers and I knocked around some time ago
and generally came to no conclusion.
My contention is that the spacer is necessary. The theory is that the 2
bearing inner races and the spacer, when the nut is tightened
essentially increase the cross sectional area of the stub axle. This
increased cross section substantially decreases any torsional deflection
of the stub axle resulting from axial loads.
As Healey stub axles are well know for cracking in near the root I am
inclined to take as much strength as I can get. I believe, but cannot
prove, that most of the cracked axles that we have come across have been
ones which were operated for some time without spacers. BWT we sent 12
stub axles out for crack testing some years back and as I recall 7 came
back with cracks marked at the stub axle root!!
I should mention that Steve, a man whose opinions I profoundly respect,
thinks my theory is complete horse feathers!!
Michael Salter
www.precisionsportscar.com
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