Forgive the basic question but:

Assuming you install the wheel bearing cups to the correct depth for your bike, what does the inner axle spacer actually DO? I know it restricts the minimum distance between the wheel bearings. But is that its' actual function - to keep the bearings and cups where the are? If you didn't have a spacer (and no, I'm not planning on running without one) would the cups have a tendency to move/shift over time? Or when you tightened the axle bolts?

 

That spacer supports the inner races of the two bearings, while the outer races are held by the bearing cups in the hub. When the axle nut is tightened the spacer is the meat in the middle of the sandwich, which has the swingarm either side, plus the outer spacers etc. Without it the bearings would jam and seize. Hope that helps!

 

Thanks. I understand exactly what you're saying. I should have mentioned that I'm taking about an older bike that doesn't use sealed bearings. So there's only one spacer. But I imagine the concept is still the same...

 

The tapered style of bearings use a central tube, but that needs to be shimmed, so the bearings have a small amount of end play when the axle is tightened up.

 

Right. There were no shims on disassembly. Just the spacer. I’m hoping none will be needed when i reassemble.

 

That may well be correct. Your FSM has the correct procedure for setting end float - don't ignore it! When buying replacement bearings some years ago from a local supplier he guessed they were for a Ford car! They use the same ritual as well.

 

 

having some float is controlled by the spacing but once there, its more important function is to lock the inner races so they do not turn on the axle. tapers are more forgiving in a way as the ball type is not done right will radius ride and not live very long.

 

That's certainly what this spacer does! Definitely will be adjusting end play this weekend, too, when I reassemble the front end.