Rear Axel And Bearing Marks

I've never looked at the construction of a single sided swingarm, but surely the axle doesn't rotate with the wheel? On 'normal' swingarms, the axle nut clamps the spacers and inner races of bearings into a rigid tubular sandwich between both sides of the swingarm, the wheel and sprocket carrier then rotate on their bearings.

 

I assume the splines on the stub axle mate with the splines just below the bearing in the photo? If yes, then I can't see how that bearing does anything either. Even if the bearing is needed and does rotate somehow the inner race certainly should not spin on the axle. What goes on top of the bearing when it's fitted on the stub axle?

 

The axle is fixed to the wheel so they spin together on the 2 bearings within the hub unlike a double sided swingarm where the wheel spins on the fixed axle. Never really thought about it but I assume the bearing in question is to accommodate movement in the cush drive ?

 

There must be something amiss there if the inner race is picking upon the axle. If the bearing doesn't rotate freely with no play I'd change it. The inner race should obviously be "locked" to the axle when the nut is tightened.

 

As @TRIPLE X rightly suggests this bearing only exists to allow the small movement required for the cush-drive to operate. As such the relative inner to outer race movement is only ever plus or minus a few degrees in its operating life. Difficult for me to comment without "hands on" but if the bearing feels smooth then it's probably just the rubber grease seal friction that you are feeling. As long as it feels smooth it's probably fine.
The fretting marks could just be from the vibration and shock loads being transmitted from the chain/sprocket drive. It might be worth inspecting the cush rubbers and perhaps replacing if there's play when assembled.

 

FYI

 

The bearings are stiff to rotate and this is normal, the marks on the axle are due to Oscillation. Col Cs post outlines this perfectly, I have stripped and serviced a number of Triumphs with single sided swing arms (SSSA), and all have these marks, a lot comes into play with the SSSA, acceleration and braking are the two main factors, a lot of torque is transmitted to the rear hub and drive train, it is testament to modern materials and product quality that the components last as long as they do. Linx it is clear you look after your machine and take care with the maintenance, I would confidently say after re building the rear assembly you will get another 24 months trouble free before another strip and re grease, some early Triumph SSSA have more component parts, more often than not the needle roller bearing on these, collapses whilst removing the splined hub.

 

If that's regarded as normal on these then I guess it's"OK".
I just can't see how/why the inner race should move on the axle when the nut is torqued up. No way should the inner race of a bearing wear the shaft that supports it, that's the whole point of having a bearing. Ho hum.

 

Are they definitely witness marks? Mine had similar marks but they cleaned off easily with nothing more than WD40 and a cloth.

 

Fretting occurs on a microscopic level, if you look at the screen shot I posted you'll see that even the example shown appears to be a bearing inner race. Crevice corrosion and galling of stainless steel are other phenomenon that occur at this level. I'm not a motorcycle technician, but 30+ years as a mechanical design engineer, these things are not unusual.

 

There's no good seal to prevent corrosion from occurring between inner races and axle. Grease needs to be applied between them all the way out to and including the threads to form a protective seal. You can see by the corrosion on the threads that it wasn't greased/sealed well.

Standard swingarms are even worse because moisture can more easily make its way directly in thru the adjustment slots (rather than the more difficult path formed by the threads) and down the length of the axle if it isn't greased well.