Coker bearings - Coker MUni

I am no in my second Coker Muni season. I drive only Coker on bumpy roads on gravel. Here in Norway it is a lot of climbs. What I have realised is that my bearings last shorter and shorter. I have now two Cokers. One Hunter/Liwevire and one Nimbus. On both my wheels I use SKF bearings. Before I used NBK. I was a bit disappointed as it now seems that I must replace the bearings at 980km. I think its because of all the climbing as you get a pressure on the side of the bearings compared to only tarmac and flat land Cokering. The gravel is also not flat, as the wheel will bend from one side to another. I do not over tighten the bolts on the frame. I have also tried to repack the bearings with grease, but it last only a short while. Anyone else had problem with bearings with Coker Muni? How often must you replace bearings?

In what way are the bearings failing?
Is the outer race getting sloppy (you can wiggle the outer and inner races back and forth)?
Is it getting packed with dirt and crud?
Is the grease getting washed out?

Open up one of the failed bearings and see what it looks like inside. You can pop off a seal from the bearing using small pointy tools. Then you can see if the bearing is full of dirt or maybe something is broken inside (like one of the ball bearings or the cage that the ball bearings fit in).

Are you using metal shield or plastic/rubber shield bearings?

For muni use I have found that expensive bearings aren’t worth it. Dirt and crud destroy the bearing too quickly. The only time that expensive bearings might be useful would be for an expert level indoor freestyle unicycle or a road Coker going for a world record. Otherwise the generic bearing (with plastic/rubber shield) will do the job just fine.

I use the SKF bearings with plastic/rubber shield. When I cycle I can feel the wheel is being hold back when the bearing is damaged. Like the brake is a little on, then after some while it is rolling fine again. Then after a while again the bearing not roll god and the wheel starts to brake. I only Unicycle in god weather. Of course it is some dust, but I don’t think that is the problem. When I take of the wheel the outer race is a little sloppy.

A friend (not Unicyclist) told me these bearings was not god on sideway pressure and give me a tips to use Spherical roller bearings. But after some reading I cant find that the Spherical bearings are made to fit the 17-mm ID, 40-mm OD Coker bearings.

I get many thousands of km on a set of Coker bearings. The exception was on my original Coker in 1999 - they shipped with unsealed (open on one side) bearings and I only got 1500km on them but I remember people riding in wetter climates only got 200-300km on them.

I do a mix of road and offroad riding, but lots of climbing either way. In fact my original Dave Stockton wheel from 2003 has now been on NUT, AUT, LUT and leaving today for MUT. Plus at least 3000-4000km of other riding. All on the original bearings. I am not positive which type they are though. It’s all packed so I can’t look. I think SKF.


It is possible that you are damaging the bearing during the process of pressing it on the hub. It is very easy to accidentally damage the bearing while pressing it on the hub, I’ve done so myself. A bearing damaged in that way will not last very long before griding or behaving badly.

When you press the bearing on you need to be careful not to put any pressure or force on the seal area of the bearing or on the outer race of the bearing (the outer ring). You should only be pressing on the inside race (inside ring). Use a short piece of tubing or pipe that just fits over the hub and is about the same diameter as the inside race (inside ring) of the bearing. A short section of 22.2mm seatpost is about the right size, or a section of electrical conduit, or a stack of suitably sized washers. You want something that is sized right so you are only pressing on the inside race of the bearing while pressing the bearing on the hub.

I also use Loctite Sleeve Retainer (Loctite threadlocker would probably also work) to help secure the bearing. The bearing is only held in place by a press fit and that is not always enough to keep the bearing from slipping on the hub. The Loctite will fix that and hold the bearing in place better than just a plain press fit. The Loctite will also act as a lubricant as you’re pressing the bearing on.

Hey man, feel free to pry off the covers and squeeze some grease into the bearings, pushing out the dirt etc. Then pop the covers back on.

I’ve spent many, many, many hours scouring the bearing info for a better bearing solution for different uni situations and, at this point, there isn’t one. In fact, your bearings are spherical single row deep groove bearings, which are a kindof mid-compromise bearings that handle both axial and radial loads in an ok way. Bear also in mind that more exotic solutions get very expensive very fast (read: cost more than your complete unicycle).

However, there should be minimal sideways pressure on your bearings. I adjusted your frame carefully to match the bearing width to eliminate that kind of pressure. However, perhaps there have been some not-gentle crashes!

Should be. Good luck Nathan and crew! And AJ too, from Austin!

I have no Crashes on my new Unicycle. A couple of UPD, but have managed to take the Unicycle in the handle before it got the ground. I think maybe I could fasten the frame a bit looser, but on my first ride it was to lose and I had to tighten it a bit more.

What kind of SKF bearings do you recommend to use? I find 10 types of 17*40 bearings on SKF’s web site.

6203 ETN9

I think John C is right

These same type, quality of bearings (just different size) I have used in motorcycles. Failures are rare, even at 50, 000 + miles. Actually, I have never had a failure, just a notchy feeling, so I replace the bearing while I change the motorcycle tire, only if it feels like it has a stick spot while moving it with my finger.:slight_smile:
Follow John’s advice on installing the bearing. I am almost certain that you are damaging it while putting it on. :sunglasses: