S.S.Bearing- What to Do about it??

[Ed Miller]

I agree. Both left and right side main bearings on 2003 Harley Twin Cam 88
inch engines are roller bearings. Up to 2002 the left side ( primary drive
side ) was a Timken tapered roller. Harley found the larger non-tapered
roller bearing eased assembly AND was able to handle much greater loads. So
much more the 2003 Harley Road King SVO bike has an 103 inch version of the
Twin Cam engine. Seems to me the way the crankshaft is made and the way the
front bearing is installed that most if not all the thrust load in an OS 140
RX is handled by the front bearing. Another fact supporting the roller
bearing theory is the '99 and half the year '00 Harley Twin Cam engines used
a ball bearing on the outer side of the rear ( cylinder 2 ) camshaft. This
ball bearing failed on some bikes. The way it was installed it handled only
axial load, no thrust load. In December '99 Harley replaced it with a roller
bearing and the rear camshaft bearing failures stopped. These camshaft
bearings are oiled solely by splash, not pressure. We might need to make
some thin shims the ID of the crank OD and OD just slightly less in diameter
than the inside edge of the roller bearing outer race for spacing. Or we
need a roller bearing with an inner race that has a small lip ( flange ) on
both sides.
All this is based on the assumption the rear bearing is undersized which I'm
not thoroughly convinced of. I'm beginning to believe not only are we
running the wrong percentage of oil in the big 2 strokes but we should also
be looking to use more Castor oil and less Synthetic oil in the blend. The
rear bearing in an OS 140 RX is larger in OD and width than those found in
all YS120-140's. The firing pulse on a YS 4 stroke is especially violent and
really tough on the con rod, wrist pin and rear bearing, not to mention the
detonation that is common on YS 4 strokes. Bearing failure on a YS usually
is the destruction of the cage whereas the bearing "failures" on the RX seem
to be roughness which indicates pits on the balls and/or the races. Rust or
dirt is usually the culprit for pits in the races and balls. Years ago I had
a YS61 rear exhaust and experienced short bearing life. I replaced that
engine with a YS61 AR which had a SEALED stainless steel rear bearing and I
never had to replace the rear bearing in that AR. I was using a 13x10 APC
and 20 to 30% nitro in that AR so it was seeing a pretty good load. Boca
sells a packed with grease, sealed, stainless steel rear bearing for the OS
140 RX, I intend to install it in my OS with the seals left intact.
Ed M.
----- Original Message -----
From: <patterndude at comcast.net>
To: <discussion at nsrca.org>
Sent: Tuesday, August 05, 2003 6:15 PM
Subject: Re: S.S.Bearing- What to Do about it??


>
> You found roller bearings that fit an OS140RX???  Please provide a
reference.
> THis would be an amazing find.  I disagree with you that these wouldn't
handle
> the thrust load.  On the contrary, our bearings carry almost no thrust
load.
> They handle radial load almost entirely.  I would think a roller bearing
would
> be a great solutions.  As evidence to this conclusion, look at what
Zenoah,
> Desert Aircraft, and other gas engine mfg do - they use roller bearings.
These
> engines are designed for far more life than modelers put on them and the
> bearings are never changed.
> --Lance
>
> --
> District 6 AVP
> www.aeroslave.com
> > In a message dated 8/5/03 4:18:50 AM Pacific Daylight Time,
rcaerobob at cox.net
> > writes:
> >
> > >
> > > Assuming that OS doesn't offer a solution to lubrication of the rear
bearing
> > > on the 1.40, what other options are available?
> > >     What mods could be made to the crankcase to permit more oil flow
back
> > > there?
> > >     Would increasing oil content of fuel make any difference?
> > >
> > > If the real core problem is undersizing of the bearing for the load
> > > application the motor endures, then a real fix would be a redesign of
the
> > crankcase
> > > to use a larger and wider bearing.  Pretty unlikely that would happen,
I would
> > > guess.
> > >     So what's the solution besides keeping the bearing suppliers
> > > well-funded??
> > >
> > > Bob Pastorello, Oklahoma
> > > NSRCA 199, AMA 46373
> > > <A HREF="mailto:rcaerobob at cox.net">rcaerobob at cox.net</A>
> > > <A HREF="http://www.rcaerobats.net/">www.rcaerobats.net</A>
> > >
> > >
> >
> > Continued - A larger bearing is a double edged sword, larger bearing
means
> > larger balls and larger diameter races and thus higher surface speed,
between
> > the balls and races at a given RPM.  I'm not enough of a mechanical
engineer to
> > say where the trade off is, but I know in other engines larger bearings
have
> > not solved the problem (OS .61).  The solution is a tapered/timpkin
bearing,
> > I've tried to find a match, but no success, the problem is that we are
using a
> > ball bearing in the wrong application, auto manufactures tried this for
years
> > on wheel bearings, tapered bearings solved the problem.  I can get
roller
> > bearings that fit, but they will not stand the thrust load.  Again,
stainless
> > has
> > worked for me, several different engines and I have a lot of
data/experience,
> > many thousands of flights on mine and others engines, most recently the
OS 140
> > and believe me I've tried all the "fixes"  Interestingly I just changed
the
> > bearing in a new OS 140 RX, just because it had 140 flights and I was
planning
> > to go to a contest this weekend, bearing seemed fine.  Turns out that it
is a
> > stainless bearing, with the seals removed (I've never found a stainless
without
> > seals).  The bearing was fine, no corrosion, I jumped the gun.  No for
the
> > rest of the story I had this engine apart for other reasons and it was a
year or
> > so back so it's possible that I just changed the bearing because I was
in
> > there, but I think I would remember and I keep pretty good records so
that is a
> > doubtful answer.  It will be interesting to see it the new engines start
> > showing up with stainless bearings or if this was a fluke, maybe they
were out
> > of
> > bearings at the factory and used the bearing from the EFI or...
> >
> > Bob
> >
> > Bob
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