So 5000 miles in and I had new tyres fitted last week (second front, third rear). Noticed that one rear bearing was a little rough when we had the wheel off at the fitters. No spare bearing there and no time to fit anyway. Dismantled tonight and thought the following may be of interest:
Once they were out I took the seals off both bearings.
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The brake side on the right here, was fine with about what I would normally expect in terms of blue almost clear grease over all components of the bearing. Bearing action was smooth with no play.
The belt side appeared at first to be full of black grease that pretty much filled the available space. There was plenty of play in the bearing too. I dissolved just the layer that was on the inside of the seals in thinners then inserted a brand new "stick" of 6mm neodymium magnets (see below) and retrieved a 1/2 inch blob of iron filings/rust from the thinners. Thats only from the thin layer on the inside of the seals, the majority of the crud was being squished around the bearings. Basically all the black crud was bits of c**p that had worn/corroded from the bearing faces and the balls.
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I broke up the ball bearing spacer and separated the inner and outer races. Both are clearly pitted.
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The bearing balls were not shiny either. There appears to be no wear in favour of either side of the race so it is unlikely this is an over tightening problem. It looks to me simply like moisture ingress has induced corrosion. The seals on the bearings did not appear to be damaged
The bike is never jet washed and I am careful about how I rinse of any wash solution with the hose pipe, knowing that these bearing are an issue. However I have done around 1000 miles of wet weather riding of the 5000, often at motorway/autoroute speeds.
Obviously new SKF bearings going in asap, front and rear........ shame there is no way of fitting a grease nipple. I am also looking into the possibility of fitting extremely high spec ceramic bearings as these are supposed to withstand poor lubrication for longer should similar happen and I am away from home.