Hello all. Sorry it has been so long since I agreed to post my findings on
this problem but I finally found out tonight. I thought this would have been
done in November but after the move to the new house, a new job at Dell
Computers (no notice on that one), buying the GT, and finally a hard drive
crash needless to say I am wayyyy behind in everything.
Tonight some friends from the MG club here in Austin came over to help me
pull the engine in the B and yes the roller bearing was a TOTAL failure. It
came out in about 20 or so metal pieces with no carbon left on it. The metal
bounced around in the housing enough to gouge out some metal from the bell
housing and the clutch cover. I did take some pics of this and when they are
developed they will be available if anyone wants to see them. The pressure
plate looks fine and the only problem was the throw out bearing. Aside I
think I am doing pretty good. I plan on refreshing the rod/main bearings,
replacing the rear seal, and de-carbonize the head while the engine is out
(it only has about 10k on this rebuild, but some track time). I am thinking
of replacing the clutch with another HD clutch w/o the roller bearing. If
anyone knows of any good sales going on for parts please let me know!
Well now to go enjoy the GT (with a stock clutch but not a 2l engine like
the B)
Don Collins
70B
70BGT
-----Original Message-----
From: Jim [mailto:microdoc@apk.net]
Sent: Thursday, October 21, 1999 10:10 AM
To: Don Collins
Cc: MG Listserver
Subject: Re: Roller Throwout Bearing
I can hardly wit to hear your findings.
Don Collins wrote:
> Well this is a very good time for this thread. About 2 weeks ago my B
> started having some vibration when ever the clutch was pushed in. Deciding
> it was time to get it home I took off and the next gear change the clutch
> went to the floor, major grinding sounds, and smoke coming out from under
> the car. I was able to place the car in 1st to get going w/out using the
> clutch and then high speed shifted it to 3rd and ran in 3rd o/d to get it
> home (no slippage in the clutch when I accelerated. Engine was running
> fine). I will be pulling the engine in about 2 weeks after I move into my
> new house to see what happened. This is a Roller T.O. Bearing that was
> replaced in 1995. If this was the cause then looks like it will be back to
> the stock T.O. bearing. Hard to say but it has only been 4 years and under
> 15K miles.
> Has anyone had this same thing happen?
>
> Don Collins
> 70B
> 70BGT
>
> -----Original Message-----
> From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net]On
> Behalf Of James H. Nazarian
> Sent: Wednesday, October 20, 1999 5:26 PM
> To: Max Heim
> Cc: MG Listserver
> Subject: Re: Roller Throwout Bearing
>
> 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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