Throw out bearing inner body

[Missionguzzi]

Take a look at a couple of pictures.  Two inner bodies for throw-out bearing on an old 5-speed transmission.  One is new, unmolested, and the bearing surface measures 5.5mm thick.  The other is old, as found, shows a deep cut and the shaft portion is squared off, and it measures 3.5mm thick.  I can't imagine what would cause this type of damage (very uniform and clean) or perhaps it was done intentionally for unknown reason.  Possibly came from the factory that way?  Any ideas?

[pehayes]

I'm a self-trained hack machinist with cheap, inaccurate machinery.  Everything about that second body tells me it was home grown and not particularly well.  Having said that, there is no reason it couldn't have worked properly for years.  The squared off stem fits into a very loose recess of the outer body.  There should not ever be much if any metal to metal contact between the inner and outer bodies in the area of this stem.  The cut in the bearing surface wouldn't be a serious issue.  It is not actually a bearing surface, just a load bearing table.  The needle roller bearing has two hardened 'race washers.  One of those race washers sits against your cut surface but doesn't actually move relative to the body.  Just sits there bearing load.  The other race washer sits against the inner face of the outer body.  Again, it doesn't actually move relative to the body.  Between the two race washers is the captive needle roller bearing.  That bearing handles all of the load and mis-match rotation between the inner and outer bodies as you pull on the clutch.

Simple answer to your question is that the obvious differences  between the good and supposedly bad parts were the created in the shop.  They were not created as a result of operation of the moto.  In addition, there does not appear to be any reason why you HAVE to abandon the part.  Replacement used parts should be widely available from the usual suspects.  Yes, while you have it all apart, I would opt to get a good used original replacement.

Patrick Hayes
Fremont CA

[Missionguzzi]

Patrick, thanks for your response.  I made the same observations you did, for the same reasons.  The inner body seems like it would be functional, and I thought about re-using it, but since I had it apart I decided to use a correct, properly-sized one.  It's just weird that someone would have made such a change, unless there HAD been some previous damage to the throw-out bearing itself, the washers and the load-bearing surface.  The transmission was in really rough shape, with bad bearings, missing detent plunger. mangled junk in the bottom, but it had a new-style 3-coil shift-return spring and a 4mm clutch hub, neither of which was original on the mid-70s Guzzi.  Obviously someone opened it up and attempted to put it back together, just without much attention to detail.