Bearing Service and Maintenance
When it comes to bearings, like most dirt bike maintenance, the goal is to prevent time-wasting breakdowns on the trails, embarassing breakdowns on the motocross track, and expensive breakdowns requiring the complete replacement of parts that COULD have lasted for years.
Hey... a dirt bike gets ridden in THE DIRT. Some of that grit and moisture is going to work it's way into your bearings. So here's a crash course in checking and servicing the bearings on your dirt bike.
The fastest way to check wheel bearings is to have your dirt bike upright, resting on both wheels, while trying to give the wheel in question a side-to-side pushing and pulling. If there's any significant play in the bearing, you'll be able to feel it.
To service or replace the bearings, you'll have to start by removing the wheel from the dirt bike. Then place the wheel on something that will hold it in place, while leaving room under and around the hub. A sturdy plastic pail works, or one of those plastic milk crates, or a wheel changing stand if you're one of those guys with the kind of shop I envy.
Before I forget, keep a small container handy to put all the small parts in as you work.
Then take your universal tool of a thousand uses – otherwise known as a screwdriver – and gently remove the rubber dust seal from the hub (some bikes won't have this seal). If you're careful, and the seals are in good shape, you can re-use them... but price out new ones at your local shop and you'll probably find they're cheap enough that you'll decide to replace them.
With the first seal removed carefully turn the wheel over (the bearing PROBABLY won't fall out, but I've quickly flipped a wheel over and had a bearing fly out and hide in a dark, hard to reach corner of my garage) and remove the seal from the other side.
Take a close look and make sure the bearing isn't held in place by a clip. If there is, remove it.
You should now be able to get your universal tool of a thousand uses (or a pin punch or drift) down the center of the hub to the inner race of the bottom bearing. With a hammer, tap your tool of choice against the edge of the bearing so that it starts to slide out of the hub. If you can't get up against the edge of the bearing race (carefully) turn the wheel over and give the opposite bearing a sharp rap. That often pushes the spacer tube against the bearing you're trying to remove. Now you can slide the loose spacer to expose the edge of the bearing race. Tap all around the bearing as you go to help it slide out straight.
When the first bearing is out, remove the spacer tube. Getting the remaining bearing out should be a lot easier.
Wipe the hub down and make sure it's clean – 1, so you can inspect it properly and 2, so you get rid of any grit trapped in the area.
If your bearings aren't sealed and you're re-using them, clean them out with solvent. You want to flush out any existing grease and the grit that may be in it. You can quickly dry out the bearings with compressed air but, if you do so, hold the bearing in place. If you let it spin you risk premature wear and damage because they're racing around without any lubricant.
To repack (re-grease) the bearing, place a dollop of bearing grease in your hand and push the bearing into and across it so that the grease is forced into the bearing. Don't stop until you see grease forced out of the top of the bearing.
When you can, use sealed bearings. They're a lot easier to maintain, and they last longer.
To install the wheel bearing, grab something just a little bit smaller than the diameter of the bearing – a socket is the most common thing that's used. Place the bearing on the hub, place the socket on top, and tap the bearing in. You'll feel and hear when the bearing is seated. Flip the wheel over (carefully), install the spacer tube, and tap the second bearing in the same way you did the first.
Install the dust seals by tapping them in place using a socket.
The headstem bearings on your dirt bike aren't much different than wheel bearings when it comes to removal and service.
Take the fork legs out of the triple clamps and remove the large flat nut on the top triple clamp. The triple clamp should lift off allowing you to slide the bottom triple clamp and shaft out of the headstem.
You can now tap the outer races out of the headstem in the same manner as you would tap out wheel bearings.
The bottom bearing can be tricky to remove from the steering shaft because the shaft usually has to be pressed out of the bottom triple clamp. It IS possible to take the bearing off the shaft using a cold chisel, but you run the risk of damaging the surface of the shaft. If you don't have a press, and can't borrow one, get a price from your local bike shop or a friendly independent mechanic for fitting the bearing. (if anyone has any better suggestions, please post them as a comment or email me)
Once the new bottom bearing is fitted install the new outer races to the headstem tube and then insert the bottom triple clamp and shaft up into the headstem. Install the top bearing over the shaft and replace the top triple clamp. Lightly install the top nut, put the fork legs back in, and tighten only the bottom clamps. With the bottom clamps tight, snug up the top nut until the steering moves freely. Finally, tighten up the top clamps.
To service or replace swingarm bearings on your dirt bike, you'll start by removing the seat and rear subframe, and then swing the rear brake caliper out of the way.
You know how you loosen all the nuts on a car wheel BEFORE lifting it off the ground? The idea is to give you more leverage. For the same reason, loosen (don't remove) all the bolts in the swingarm linkages while everything is still attached.
Then remove the nut on the end of the main pivot shaft –where the swingarm is attached to the dirt bike -- and tap the shaft out of the frame.
Remove the bolt that mounts the bottom of the rear shock to the swingarm and disconnect it.
Slide the swingarm out of the pivot point.
Now, with the swingarm on your bench, garage floor, or antique dining room table, you can disassemble each bearing one at a time to keep the parts from getting mixed up, or have a separate container for each bearing (label each one).
If the bearings have caps, carefully pry them out with a screwdriver. Then push out the inner bushing and expose the bearing rollers.
Clean the bearings carefully, using the same technique as wheel bearings, and inspect them for wear.
On one of my bikes, the roller bearings are “loose” and can fall out and disappear. When I'm reassembling the bearings, I smear grease in the outer race and “stick” the rollers in place. Everything stays in place until I get the inner bushing in place.
It's always a good idea to inspect the dust seals and replace them as needed.