Bearing Question

Thanks for the link:


There's also an interesting PDF on that page:

From the PDF:

Damage Condition

Wear occurs due to repeated sliding between the
two surfaces. Fretting occurs at fitting surface and
also at contact area between raceway ring and
rolling elements. Fretting corrosion is another term
used to describe the reddish brown or black worn
particles.


Possible Cause

Poor lubrication
Vibration with a small amplitude
Insufficient interference


Countermeasure

Use a proper lubricant
Apply a preload
Check the interference fit
Apply a film of lubricant to the fitting surface

I'm assuming that if there's movement then these bearing need more frequent inspection as well. For example there's no getting away with anything less than an annual inspection.

Click http://www.nskamericas.com/cps/rde/xchg/na_en/hs.xsl/fretting.html

With a slip fit at the axle and bearing are, and near zero preload as close as humanly possible, there is every likelyhood that the bearing will move a little. The weight of the trailer bearing down on that spot and the free rotation of the rollers within the race should keep them from moving but it's not a guarantee. There is nothing to locate them on the axle and keep them there other than proper tension and some prayers. If you used Loctite or similar you'd probably have a hard time getting them off next time. I have the same marks on my bearings. It's normal with the tolerances involved in today's trailers.
Sorry for the link. Puter won't let me access the tool bar. Maybe someone can make it a clicky for us.
http://www.nskamericas.com/cps/rde/xchg/na_en/hs.xsl/fretting.html

The inner race should not rotate, even slowly. That would be bad news. The axle isn't designed to accommodate that. The balls rotate between the inner and outer races, that's the way it works. If the inner or outer race rotates, that's bad and should be repaired...immediately.

The inner race slides on the axle and rotates slowly on the axle when in use. This is normal and desirable as it spreads out the wear.
I have seen that burn looking mark on a lot on bearing races.

myredracer wrote:
Maybe you could check for uneven clearance around the shafts with plastigage?

I don't see how you could use plastigauge with a press on bearing. I doubt if there is a measurable amount of clearance.

Whatever you do, if you find the corresponding "stain" on the axle shaft, do not take some sandpaper/emery cloth and try to polish the "stain" away. The last thing you want to do is remove material from the axle shaft.

The "stain" looks like a bit of fretting and, at this point, won't hurt a thing. A little anti-seize or grease will help alleviate the problem. It probably won't completely eliminate it, but it will help. It's caused by minute movement between the axle shaft and the bearing.

Maybe you could check for uneven clearance around the shafts with plastigage?

Good question. The top and side of the shafts looked like new. I did not visually inspect the bottom (I should have). I think the bottom is where the weight would be. They felt fine when smearing a thin layer of grease on them.

I will be more methodical with the other side. Assuming the marks are on the other other side too, I'll pull the bearings and look specifically for the marks with an effort to note where the mark mated up to the shaft and inspect the shaft more carefully.

Not a bearing expert, but what do the corresponding areas on the shafts look like? Could this be on the side that would carry more vertical load and the bearings were a hair too loose or not seating correctly against the shafts? The way the "stain" is about 120 degrees around the circumference and looks to be a bit wider at the center of it kinda suggests that??