Wednesday, February 21, 2018

Inspect your wheel bearings!

Last winter I built up a set of burly new wheels for my WR250R using SM Pro hubs, Bulldog stainless spokes with aluminum nipples, and SM Pro rims. While the combination was almost identical in weight to the WRR's stock wheels, the heavier spokes and higher tensions translated into noticeable handling improvements and the larger bearings of the SM Pro hubs (in theory) should have improved durability.

So, while tearing down my bike recently for a pre-season inspection, I was surprised to discover that one the rear wheel bearings had completely seized despite there being no obvious signs of damage to the bearing itself, although the end cap showed some suspicious, uneven scoring past the seal.

The OEM rear hub uses one 6005 bearing on the drive side and a smaller bearing on the brake side. Here's the bearing replacement kit for the OEM hub. The loose bearing lying on top is also a 6005.

By comparison, the SM Pro rear hub uses three 6005 bearings: two on the drive side, and one on the brake side. It was the inner bearing on the drive side that had seized, which struck me as the least likely bearing to fail unless there was some sort of manufacturing defect. True, these wheels saw some wet conditions last year, but after only 7,000km I wasn't expecting a seized bearing. The outer bearing on the drive side showed some corrosion but remained buttery smooth, as did the bearing on the brake side.

Here's the brake side of the SM Pro hub, with external seal removed:

And here's the drive side:

Removing the SM Pro bearings is relatively straightforward using a drift to knock aside the inner spacer tube and then tap out first one side, then the other, by driving on the inner races.

Rather than buy Moose or All-Balls replacements, for about the same price (or less) I picked up some better quality SKF bearings and seals from a local distributor. The 6005-2RS is a common part used in many industrial and recreational applications, so you can get them pretty much anywhere--including where sleds and ATVs are sold.

Installing new bearings was equally straightforward once I found a 34mm socket to use as a driver. I would've made a tool, but didn't have any rod stock in the required diameter. Sometimes buying a socket is good enough.

With new end-caps installed, the wheels feel buttery smooth again. Here are the old ones showing part numbers:

The lesson here is to not assume that even relatively new bearings are still good, and to check them all carefully before heading out on your next adventure.

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