Q. My 10-year-old SV650 is coming up to new tyre time and I was told to watch out for wheel bearing seals and spacers with high mileage bikes.
The thing is, I don't actually know what I'm looking for when they're on the way out!
Jmccomas, MCN forums
A. On most bikes the axles are steel and fit snugly into the rubber lip seals in the wheel that are supposed to keep water out of the bearings. At the bolt end the axle is smaller to pass through the bearings, so a spacer has to be fitted - it's obvious in service manuals or when removing the wheel.
The spacer is aluminium and soft, so it's normal for the rubber seal lips to wear deep grooves in the spacers over time. Trouble is that then the seal is looser and lets water in, especially the front, so bearings get water in and fail (jet washing is death for these bits, so don't, but all season riding doesn't help either).
Regular cleaning and re-greasing of the spacer and seal should help prolong its life, but aluminium spacers will groove. When you do have to replace the bearings and seals put in new spacers too.
Rusty marks on the spindle or around the bearings themselves are early warning signs. The spacers are aluminium and not steel because it saves on unsprung weight and improves handling.