Recap: This is a series of posts about replacing the fork bearings on a TiLite Aero wheel chair.
In the first post, I removed the forks from the chair. What should have taken about five minutes actually took several hours, owing to a bearing that was rusted solid onto the fork axle.
In the second post, I worked through all the details on bearings. As long as you know the size of the steel sealed bearings that you need, you can pick them up for around $1 each on Amazon.
This third post is about driving the old bearings out of the fork, and pounding the new bearings into the fork, using only these tools and materials:
- snap-ring (c-clip) pliers
- hammer
- screwdriver
- improvised bearing drift: 13/16″ spark plug socket (YMMV)
- a smear of grease.
- a surface to pound on.
- a soft vise to hold the forks as needed (I used a Workmate bench).
The snap-ring pliers are not optional, unless you’ve got a whole lot more dexterity than I do. There is one c-clip in each fork, whose purpose is to ensure that the bearings do not slide down from the weight of chair and user. That c-clip is difficult to get in or out without c-clip pliers.
Also, be warned that driving the bearings in with a hammer and “drift” is not for the faint of heart. You end up hammering pretty hard. About as hard as you might when pounding a nail into a 2×4. You have to do that, to get the bearing to seat all the way at the bottom of the hole it fits into.
If the very idea of hammering that hard on an expensive wheelchair part makes you squeamish, then you’ve got good sense. This is nobody’s idea of a good time. But once you’ve started this, either you drive that bearing all the way home or you buy/make a bearing press that can finish off what you started.
If I had to do this multiple times, I’d shop for a bearing puller (to take the old ones out) and a bearing press (to push the new ones in) before I started the repair. There are also kits specifically marketed for common wheelbearing sizes (e.g., a kit for pulling and pressing in R8 bearings).
But you can do it with just the crude tools listed above. That’s how I did it, for this one-off repair. That’s really the point of this post.
Get the old bearings out using screwdriver and hammer.
The basic idea is simple. You’re going to push the top bearing out of the top of the fork. (As shown above, you’d be pushing it from below, so that it moves toward the camera.) Then remove the c-clip, using c-clip pliers. Then push the bottom bearing out of that same opening.
In other words, the top bearing comes out first, then you remove the c-clip, then the bottom bearing comes out. And all of that comes out of the top hole in the fork.
To achieve this you:
- Flip the fork over (from what is shown above), and hold it in some fashion. I used a workbench as a soft-sided vise. If you are careful, you can simply rest the flat top of the fork on a couple of cutting boards, or chunks of wood, but you must leave the full width of the hole unobstructed so that the bearing can come out.
- Insert a flat-bladed screwdriver through the bottom of the fork (the side away from you, in the view above).
- Catch the corner of the blade of the screwdriver on the inner bearing race of the top bearing. (The one nearest the hole that these must come out of).
- Give the screwdriver a sharp tap.
- Move the screwdriver so that it catches the opposite side of the inner bearing race of the same bearing.
- Give the screwdriver a sharp tap.
- Move the screwdriver blade back to where you started.
- Repeat 2 – 6 until the bearing falls out of the top of the fork.
You keep moving the screwdriver from side to side, as you tap these bearings out, to try to ensure that the bearing stays level within the fork — perpendicular to the axis of the hole in which the bearings sit. The last thing you want is to get the bearing wedged kitty-corner in that hole.
What makes this hard is that these are interference-fit bearings in a metal casing. The hole they fit in — in the fork — is just slightly smaller than the diameter of the bearing. So, while the bearing is friction-fit to the housing, there’s a lot of friction involved.
Which means, in no uncertain terms, you are going to have to tap these vigorously to get them to move. And yet, not so hard that you break them.
How much force? Take a look at this fellow, around 30 seconds into the video to get an idea of what a “tap” is likely to be, for driving a steel bearing out of a metal bearing housing:
He doesn’t bother to move the screwdriver from side-to-side for that particular bearing. But you will want to do that here, particularly for the second bearing, which has to travel quite a ways before it is free.
A better view: This next video provides an excellent view of what you’re trying to do with the end of the screwdriver, at around 1:10 into the video. (Though, this particular bearing came out quite easily.)
Too easy: Here’s yet a third example of this technique, around 30 seconds into this video, where the bearings are driven out of a plastic wheel. You’ll have to hit harder than this to drive them out of the titanium fork.
I hope that gives an adequate feel for the process. Catch the edge of the back side of the inner bearing race with a screwdriver. Tap with as much vigor as necessary to move the bearing. Move the screwdriver from side-to-side on the bearing to help keep it aligned within the bore. Keep tapping until the bearing drops out.
Remove the c-clip. And do the same thing to the other bearing.
Clean up, grease up, test the fork axle.
Clean any gunk out of the inside of the fork. It is particularly important to make sure there is absolutely nothing stuck in the “corner” of the bottom of the hole.
Why is that important? Above you see the c-clip groove, inside the fork. The first bearing you put in must be driven completely below that groove. Then you place the c-clip in that groove. Then you drive the second bearing into the rest of the space. If the first bearing doesn’t sit absolutely flat on the bottom of the hole, you won’t be able to get the c-clip in. And that, in turn, prevents you from correctly re-assembling the fork.
Wipe any gunk off the c-clip at this point, as well. Just for good luck.
Coat the inside of the fork with a layer of thin grease. I think lithium grease is what is what is typically recommended. Some say that this helps prevent the bearing from seizing in the fork, so that you can get it out next time. I say it helps lube the bearing going into the fork, because you’re going to need all the help you can get to drive the bearing all the way into the fork.
So spray a little grease in, move it around, then swab it out with a paper towel. You want just the thinnest possible layer of grease.
Test to see if the new bearing will slide over the fork axle. You’ll note that I barely bothered to clean up the axle. In particular, I don’t want a nice shiny raw metal surface on that axle, because that just invites corrosion. Leave it alone if you can. The only thing that matters is that the new bearing can be slid over it. Assuming it does, slide the new bearing off, and apply a thin layer of grease over the fork axle. Wipe off any excess with a paper towel.
A brief calculation on freezing the bearing and heating the fork.
I’ve driven bearings like this many times. It’s always a stressful process. I’ve learned to take every advantage I can, if I’m unsure that I can drive the bearing into its housing properly.
Common advice for this next step is to put the bearings in the freezer to cool them, and take a heat gun to the bearing case (the fork, in this case) to heat it. The idea is the take advantage of the coefficient of thermal expansion of metals, and give you a little extra room as you are driving the bearing.
Based on this reference, and my calculation, taking a 1 1/8″ diameter bearing from 70F down to 0F, while heating the titanium housing an equal amount, should increase the clearance for the bearing by almost a thousandth of an inch.
Believe it or not, it is well worth doing that, given that these are more-or-less zero clearance bearings.
If you are unsure of your ability to drive this bearing into this housing, go ahead and take the time to freeze the bearing, and use a hair dryer or heat gun to heat up the fork.
If nothing else, it’ll give you the courage to bang all that much harder at the next step.
BUT THIS COMES WITH A WARNING: WORK FAST. The coefficient of expansion of steels is higher than that of most titanium alloys. The upshot is that if you heat both the titanium fork and the steel bearing, the steel bearing will expand more than the titanium hole. The bearing will actually get tighter, not looser, in that hole. So if you’re going to try this freeze/heat trick, you need to get the bearing seated before it warms up to the temperature of the titanium fork.
As a compromise, you could just freeze the bearing, and leave the fork alone. That will help some, and there’s no harm done if the bearing warms up to room temperature during this process.
Bearing abuse, or using a drift to install the new bearings.
Normally, at this stage, you’d say “installation is the reverse of removal”, and leave it at that.
But in this case, that’s wrong.
To be clear, what you just did to remove the bearing — pounding on the center bearing race — ruins the bearing. At least, if you beat on it hard enough it will. All the force of your hammer blows was transmitted through the “innards” of the bearing, in order to get the outer race to slide along the bore in the fork.
You are NOT going to do that when driving the new bearings back into the fork. Instead, you are going to drive the new bearings by beating on the outer bearing race only. Never on the inner bearing race. That way, the force of your blow is transferred through the steel race directly to the side of the hole. And you are not counting on the “innards” of the bearing to transfer the force of your blows to the outer race.
Clear enough? These bearings come out one way, but they go in in a different way. Beat on the outside race ONLY as you put them back in, because you don’t want to break your brand new bearing.
This is where you need to find a drift for your bearing. A drift is some sort of sturdy hollow metal cylinder that’s just a fraction of a hair smaller in outer diameter than your bearing. The idea is that as you beat the bearing down into the fork, using the drift, it only beats on the outer bearing race, and does not press on any of the “innards” of the bearing. You can buy sets of drifts in graduated sizes on Amazon. But, typically, you’ll use a socket, out of socket set.
Beating the first bearing flush.
Here are the issues.
First, you’re beating a metal bearing into a metal bearing housing — the fork. That’s going to take quite a bit of force. And the further you beat it into the fork, the harder you have to hit it to move it. So, you start off with taps, and you end up with hammer blows.
Second, until you have the bearing flush with the opening, it’s critical to keep the bearing level — going in evenly all around. Stop every so often and eyeball the bearing. If it’s high on one side, tap that side down, and then carry on. So, center the bearing on the opening, nice and level, and start with gentle taps — on the outer race only. (If you have a brass-faced hammer, this would be a good use for it. I used a steel carpenter’s hammer.)
Eventually, you’ll get the bearing driven flush. That’s when you need to center the drift on top of the bearing, and start pounding it home. No more tap-tap-tap. At this step, it’s bang-bang-bang. You must drive this all the way to the bottom of the hole or you won’t be able to re-assemble the fork correctly.
Once you have the first bearing driven home, use your c-clip pliers (and fingers, and screwdrivers) to get the c-clip firmly seated in the groove. There are no style points here — however you can get the clip to seat in the groove, that’s fine. Note that once the clip is correctly in the groove, almost all the clip is hidden.
Finally, drive the second bearing in flush with the surface of the fork. Same process as the start of the first bearing, being sure to tap-bang only on the outer bearing race.
Pat your self on the back if the result looks like this. The outer race is flush all around. And nothing is obviously broken.
.
You’re done
Slide the fork onto the fork axle, put on the washer and retaining lock nut. Tighten the lock nut just enough to keep the fork from rattling.
And you’re done.
If all this pounding on expensive metal parts is off-putting, consider using bearing puller/press designed for this size of bearing. For sure, if I did this routinely, that’s what I would do.
An end-note on cheap bearings
I’ve watched a lot of YouTube videos on this topic, and I’ve seen a lot of people do things to sealed bearings that they really shouldn’t. Take the seals off and grease them. Change just one of a pair of bearings, because only one was thoroughly worn out. Pop a bearing out of its fitting and put it back in the same fitting. I have also seen my wheelchair-using friend hesitate to change bearings, or wait until the bearings are obviously worn.
All of this arises, I think, from the notion that these bearings are somehow precious. If a set of bearings for your caster wheels is $40, you might think about taking some non-recommended steps to try to prolong their life.
And that, in turn, derives from the ludicrous prices charged for these commodity bearings by DME suppliers.
Hence the importance of the just-prior post.
You can easily buy commodity steel sealed bearings, in sizes to fit wheelchair fittings, for around $1 each. Sealed bearings are designed to be disposable. They are not designed to be serviced. And at $1 each, it’s no hardship to treat them as the disposables that they are.
I hope this series of posts has been helpful.
