Motorcycle wheel bearings get a seriously hard time. They are exposed to the elements, in the middle of a rapidly rotating disc. They take enormous gyroscopic forces as the bike is turned, impact forces every time the bike hits a bump and are spinning at several hundred rpm just for good measure. Plus in most cases they get hammered in at the factory and then ignored for the rest of their lives. Add to that the occasional jetwash - either deliberate from well intentioned but thoughtless owners or co-incidental fromt heir location out in the real world and you have a recipe for disaster. Manufacturers do their best to mitigate it with dust seals and heavy duty grease, but the simple truth is that, sooner or later, you will experience a failed wheel bearing.
So let's start at the beginning. How do you know the bearing has failed? In my case I noticed a faint kick through the bars and a strange tinkling noise which then went away. The bike became harder to steer and less precise feeling, but the problems only became really obvious when it was raining hard and I was braking and turning less aggressively. Then the front felt absolutely horrible.
Let's look at how you actually check to see what's gone wrong.
IMPORTANT NOTE. THERE ARE THINGS IN HERE THAT COULD HURT YOU OR OTHERS. PLEASE DO NOT DO ANY OF THESE THINGS IF YOU ARE NOT COMPLETELY CONFIDENT IN YOUR ABILITY TO DO THEM SAFELY.
You will need an assistant. Assuming your bike only has a sidestand, put it into gear, turn the ignition off and, with the bike on the stand, position yourself level with the seat on the left hand side and carefully pull it over toward you and slightly backwards until it is balanced on the rear wheel and stand. It's easier than it sounds, but you will be supporting your bike and it could potentially fall on you. If in doubt, don't do it. Turn the handlebars all the way to the right and let go. They should flop straight over to the other left. If they don't, or if you have a steering damper, you'll need your assistant to grab the fork legs and try to move them forward and backward. He or she should not feel any movement at all. Assuming that all checks out, put the bike back down and go around to the front wheel. Grab the top and bottom and try to waggle it sideways. Any movement whatsoever means the bearings are shot.
By the way, you should do these checks if you're buying a second hand bike, too.
For the rear you definitely need an assistant. Again with the bike on the stand, go round to the left and, HOLDING THE FRONT BRAKE ON, pull the bike forward and towards you so that it is balanced on the stand and front wheel. It's still quite easy when you know how, but the potential for injury and damage is real, so don't do it if you're not sure. Get your assistant to grab the swingarm and try to move it sideways. Any movement at all is a bad thing. Now get him or her to do the same with the wheel, trying to rock it from top and bottom. Again, no movement is good.
So. Let's assume your front wheel bearings have failed. You have two options. Pay someone else quite a lot of money to change them or do it yourself. It's not a hard job, but please remember that a catastrophic failure of a wheel bearing at speed will have you off the bike with potentially diastrous results, so if you're not a reasonably competent mechanic I'd suggest enlisting the assistance of someone who is.
One thing to note. This technique does NOT work for Ducatis with hollow wheels - they plough a different furrow, and as I've not had cause to do one I an't give reliable advice.
As with many jobs, preparation is the key. One thing you really, really want to do is get replacement bearings before you take the old ones out. They are not expenzive - at current (August 2014) prices I should be surprised if you pay more than £25.00 for the pair. You may as well buy replacement dust seals at the same time. It's worth noting that manufacturer's original bearings are only generally sealed on one side, while good quality third party bearings are completely sealed. No prizes for guessing which is the better option...
You will need:
Front and rear paddock stands
A suitable surface for hitting a wheel fairly hard and with space for the bearing to come out downwards
A large hammer
A metal rod about 450mm (18") long - a good quality screwdriver with a hammer-resistant head is ideal - to extract the bearing
A hard metal object slightly smaller than the outside diameter of the bearing (to drift the new bearing in)
Replacement bearings (and dust seals)
Gloves (for handling very cold things)
Take your time on all the steps, work logically and you should have no problem. If something really won't shift then maybe you've missed something. Check again and, if the worst comes to the worst, ring your friendly neighbourhood dealer and ask them for advice.
Check your new bearings are the right ones, look for any indicators on them which may say they are handed or have a specific rotation direction. Then put them in the freezer.
Take off the front wheel, remove any spacers and note where they go. Clean the bearing area up as much as possible with Muc-Off or similar.
Put the wheel flat on your work surface. I used a Black and Decker Workmate, which is ancient but does the job beautifully.
Look down the axle hole. You'll see the inner face of the bearing nearest you and then a tube. Push the tube to one side and at the other end you'll see the inner face of the opposite bearing.(See the picture on the right)
Get your screwdriver or other hitting implement and put it against that little lip. Then whack it with the hammer. Push the tube the other way and hit the opposite side. Do this a couple of times and then turn the wheel over. Hopefully you will see the dust seal being pushed out by the bearing. You may also have felt movement. Assuming this is the case, turn the wheel back over and keep going until the bearing and dust seal fall out, followed by the inside tube.
Turn the wheel over. There's no tube in the way now so you can either use a socket and extension to hit the whole bearing or just do the same again with your rod. Either way, knock the other bearing out.
If your efforts don't get the bearing moving, remove the dust seal to make sure there's nothing stopping it coming out (like a circlip). You may be able to pop the seal out with a screwdriver, but to be honest you'll probably end up tearing it so be prepared to replace the seal. If there's nothing obvious stopping the bearing coming out, let it soak a while in penetrating oil then turn it over and just hit it harder. You could try gently heating the wheel around it, but be careful as aluminium melts at quite a low temperature.
Once everything is out, collect it all together and make sure nothing has escaped. You should have two dust seals, two bearings and a central spacer. Take a look and see what's failed. One of the bearings probably looks similar to the one on the right at the top of the page, but perhaps it's not that bad yet. regardless, look for scoring and other damage to the wheel itself where the bearings fit. It's a good idea to clean everything as thoroughly as you can at this stage - don't worry about the old bearings but the rest, including the wheel spindle, are definitely worth the effort. Put the dust seals, assuming they're not ruined, in hot soapy water and give them a good wash. The one where the bearing failed is probably full of gunk so it may need degreasing. Obviously, if you have replacements then don't worry about them either. This is a good opportunity to explain how it all goes together with the aid of a picture:
Part 1 is the wheel spindle. Parts 2 and 4 are the bearings, and 3 is the middle spacer. 5 is an external spacer which fits between the wheel and the fork leg. I've eft a gap between the parts for clarity, but normally the thick part of the wheel spindle, the centre scaer and the outside spacer would squeeze against the inner parts of the bearings and, when the wheel nut (not shown) is done up clamp the whole thing into a solid axle. That centre spacer is really important, as it stops the middle of the bearing being pushed in by the axle nut being tightened.
Once everything is cleaned up, get your tools ready to fit the fresh bearings. You can put a touch of grease in the housing if you want - it doesn't really matter. Double check that your drift will fit into the recess for the bearing without getting stuck. Note the rotation arrow on the wheel (it'll be stamped on a spoke) if that's relevent. Then get your bearing out of the freezer (just one), make sure it's going to be rotating the right way if that's important and that, if it's an OEM unit that is only sealed on one side, that the seal faces out. Then carefully hammer it in using the drift as a driver to spread the load evenly. Make sure it's going in straight - after a little way that's the only way it will be able to go in - and keep going until you near the note change when you hit it - it's very distinct. This tells you that the bearing is fully home. Give it a few gentle taps at all angles to be double sure it's straight and replace any circlips you may have had to remove.
Then turn the wheel over and pop the middle spacer tube in.
SERIOUSLY - DON'T FORGET TO PUT THE MIDDLE SPACER BACK IN UNLESS YOU WANT TO DO ALL THIS AGAIN.
Now with the spacer in place, go and get the second bearing out of the freezer. Again, make sure the seal faces outwards and it's rotating the right way if necessary, then use the drift and hammer to drive it home.
Pop the wheel spindle through the new bearings to make sure it's all straight. The spindle should go through very easily without any resistance. If it's hard to get through both bearings then something is probably not straight.
Before the dust seals go on you should be looking at a bearing that is seated pretty much like the one on the right. The numbers (60/22) in the eleven o'clock position are the bearing size - outer and inner diameters - which you need to check when you buy the new ones. They may be punched into the metal as well as on the seal.
Assuming everything is OK, take the wheel spindle back out and use the same drift to get the dust seals back in. It's surprisingly difficult but they really do go...
That's it. Double check that you've not forgotten anything (like that centre spacer) and then put the wheel back in the bike. Remember to check it's rotating in the correct direction and ensure that the external spacer gets refitted. Tighten everything up to the recommended torque settings, make sure you pump the brake lever to push the pads back out and you're done.
Congratulations. You've just saved yourself a fair bit of money and probably bonded a bit more with your bike, too.
Now I know MotorbikesToday readers are intelligent people. but let me reiterate - this is advice given free of charge and you take it at your own risk. There is a genuine risk of injury in some of the things I mention here. If you're not confident in manhandling your bike or carrying out basic mechanical procedures I suggest you enlist the assistance of someone better able to do the work.
Oh, and why put the new bearings in the freezer? To shrink them a little - cold metal contracts and that just makes them a little bit easier to get into the housing...