[R-390] R390/URR PTO Bearings

[Kevin Schuchmann]

Drew, Larry,

  Well I decided to take the plunge and pull it apart, very clear I am not the first 2nd or 3rd here.

No dessicant packs were found inside but it looks like it's suffering from a poor cleanup of a broken dessicant bag in the past.

Nothing corroded inside but a overabundance of grease mixed with graphite and something gritty.

Good news is the front bearing is smooth and in good shape, expected a rear bearing but it's only a bushing which is also in good shape.

What is not good is a rear thrust bearing which is the source of the rumble, the bearing itself is in OK shape once cleaned, it's the plates it rides against that are in bad shape. I'm somewhat confused at what I see, one plate has what looks to be a raceway the other plate does not, the one that does not is the one that is chewed up the worse. Are both of these plates suppose to have a raceway? are neither suppose to have a raceway and this is just damage and wear I see.

Flipping the one plate and using the raceway in the other the bearing is much smoother but is still a little rough, flipping both plates then it is smooth as glass.

At this point I'm thinking the best option is a thorough cleaning, flip both plates, grease and reassemble.

Here is a link if anyone wants to see the thrust bearing I'm talking about.

https://www.dropbox.com/s/r3we7ohxb793q3s/bad%20bearing.jpg?dl=0


Thanks
Kevin









‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Monday, March 22, 2021 8:17 AM, Drew P. via R-390 <r-390 at mailman.qth.net> wrote:

> Kevin wrote:
>
> "The bearings in my Collins built PTO have a pronounced rumble to them, dried out grease is my bet.
> Does the group have any words of wisdom or warning to flushing them out and re-greasing or is replacement the only option?"
>
> These bearings are relatively lightly loaded and should last a very long time, and so pitting due to wear is not so likely. The other cause for pitting would be corrosion. There have been on this forum reports of the PTO's internal dessicant packs breaking open and making a corroded mess of the PTO's insides - such could include the bearings. If your PTO's internals are clean and uncorroded, chances are that the bearings are not pitted.
>
> With a good cleaning and relubrication, I fixed a similar problem, hard-to-turn tuning knob, cause of the infamous R-390A Wrist Syndrome, in a Cosmos PTO (R-390A). I soaked the lead screw, lead screw nut, and lead screw bearing for several days in lacquer thinner. The lubricant of choice would be a light synthetic grease. Synthetic is preferred as it does not gum up or solidify as readily as does conventional grease.
>
> Drew
>
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