Maybe that explains why the roller bearings sometimes work (concentric) and
sometimes don't (eccentric). Good 'splanation Max!
Jim
Max Heim wrote:
> I think someone said the issue was concentricity; i.e. the MGB clutch arm
> is not designed in such a way as to perfectly center the throwout bearing
> on the axis of rotation, every time. For the "friction" type of bearing,
> this doesn't really make any difference, which explains the
> "shortcomings" of the original design in this context. But the roller
> bearing assumes concentricity of rotation.
>
> Think about it. If the axis of rotation of the roller bearing, when
> applied, doesn't precisely match the center of rotation of the clutch
> disc, you get an effect like a tiny bicycle crank. This would cause
> vibration, and enormous side stresses on the bearing, which it might not
> be designed to support for long.
>
> Of course, if your clutch arm components and bushings were all new, you
> might have something close to concentricity, and thus enjoy reasonably
> long roller bearing life (as many have reported). But if your clutch arm
> was anything like mine (when I last replaced my clutch), with worn-out
> bushings and pins and ovaled-out holes, no two clutch pedal applications
> would result in the same alignment, and you'd probably experience
> catastrophic or premature failure (as has also been reported).
>
> Anyway, I think that is a plausible explanation of both sides of this
> situation...
>
> James H. Nazarian had this to say:
>
> >Chris,
> >
> >I quote British Automotive:
> >
> > "Before you consider installing aftermarket ball/race type throw out
> >bearings,
> > be sure to read the following information. If you have already installed
> >this type
> > of bearing, it is doomed to failure. Presently there are two styles of
> >ball/race
> > type bearings available:
> >
> > 1.- A black plastic housing type
> > 2.- A steel housing type
> >
> > Both of these types of bearings suffer from premature "run-dry"
> >conditions
> >and
> > their failure is directly related to being in continual contact with the
> >clutch cover
> > thrust pad. No.1 will self destruct in a very short time; No.2 will
> >survive much
> > longer and failure will not be as catastrophic."
> >
> >Why would a sealed, permanently lubricated roller bearing designed for
> >continuous operation with load applied along the axis of rotation, run dry?
> >Could it be defective? Or damaged during installation? If so, was it returned
> >to and examined by the manufacturer? If so, might we see their analysis or
> >reply? If Doug's right, I've been driving several time bombs for the past 15
> >years. Maybe Doug will share some of his exhaustive test data and methods
> >with
> >us.
> >
> >Before I ask Mr. Moss to fly out to Ohio to help me change all these heavy
> >duty
> >roller bearings back to the original graphite type, I think I need to see
> >some
> >proof. Thanks in advance for enlightening us.
> >
> >Senior Doubting Thomas
> >
> >AKA Jim
> >1960 MGA
> >1974 MGB-GT
> >and a pool of other octagonal delights
> >
> >Chris Attias wrote:
> >
> >> Peter C. wrote:
> >> "A few quick thoughts. Roller bearing or carbon.... don't "ride" the
> >> clutch. The only time that a clutch can become worn is when your foot is on
> >> the pedal. If you don't touch the pedal, the clutch wont wear."
> >>
> >> This seems to disagree with what I understood about the design of the
> >> MGB Borg & Beck clutch assembly. See Doug Jackson's write-up on
> >> clutch bearings @ www site:
> >> http://www.mgbmga.com/tech/index.html
> >>
> >> While I realize Doug has some commercial interest in his development
> >> of a fix for the problem he finds with roller bearings, he does
> >> exhaustive research and shares his experimentation and research
> >> freely...(No commercial interest disclaimer...)
> >> Chris Attias
> >> '64 MGB
> >> '84 Alfa Romeo GTV-6
> >
> >
>
> --
>
> Max Heim
> '66 MGB GHN3L76149
> If you're near Mountain View, CA,
> it's the red one with the silver bootlid.
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