2008 KMX Cobra front wheel bearing replacement

I recently bought a second-hand KMX Cobra - about 12 years old. It has emerged that at least one of the sealed bearings in the two front wheels has failed, and needs to be replaced. I have removed the right-hand front wheel from its spindle, and the two bearings are now visible. Both are apparently identical NBK R8-2RS bearings. They are a tight press fit into the hub, and seat against some kind of shoulder inside the hub. I have no idea how to remove them, since I do not know how the hub is made. I suspect that the shoulder is actually the edge of a removable liner inside the hub and that the whole assembly can be knocked out with a suitable drift, but a little light tapping has produced no movement at all, and I am reluctant to hit it any harder until I know exactly what's inside. I was also struck by the lack of seals and washers on the assembly. Does anyone have any experience of removing the bearings from this specific model? It doesn't look like any of the exploded diagrams I have seen of other trikes.
Many thanks.

 

Have you checked their website for technical info? You also might try contacting them.

 

I know Willie G does...I'll see if I can get him on here to comment.

 

Thanks, both. There's nothing about this on on their website, and KMX's exploded diagrams in their Cobra assembly manual do not show the inside of the hub or the bearings. I have written to KMX, but I would also like to hear if anyone has personal experience of taking the assembly apart, and what problems, if any, they encountered along the way. I wonder, for instance, if all makes of bearings of the same nominal size will fit as well as those originally supplied. When (if?) I manage to get the job done, I'll post my experiences with it so that anyone finding themselves in the same position will have some thing to refer to.

 

Hello again. Are you there, Fastolfe? I was unable to contact you. I have managed to remove the bearings from the front wheel of my oldish KMX Cobra. It was not easy. If you are attempting to do this job, I hope you will benefit from my experience. I have no idea if other KMX trikes are made this way, or if the design of the more modern Cobras has changed, but the key fact you need to know is that the internal 'tube' against which the bearings seat is not a tube at all. The shoulders of it are machined in, and are integral with the seating of the bearing housings, if that makes sense. This is how I was hoping it wouldn't be. The point is that you cannot knock one of the bearings out by hammering the other end. The inner bearing is flush with the hub but the outer bearing is recessed. I had hoped to be able to drive the flush bearing out from the other end with a suitable drift. This is not possible. You need to be able to pull one of the bearings out. It doesn't matter which one. Once you have removed one, you can then drift out the other one. I know this now, but I didn't find it out until I had already made a mistake which turned out to quite serious. I knew that the flush bearing was going to have to be replaced, so it didn't matter if it got damaged, but could not think of a way to get it out. I ended up cutting tiny pieces of the bearing out using a Dremel cutting disc and worrying the bits that were left with a variety of screwdrivers etc. The main thing is not to damage the bearing housing (and of course, you have to take off the brake disc before starting). Having prised out the bearing balls, I realised that the hole I had made was now big enough to pass a wooden drift through which enabled me to knock out the outer bearing. Two good whacks, and it came out cleanly. It's probably OK, but I am going to replace both bearings now anyway. The problem was at the inner end. Although I removed most of the bearing, its outer ring was still hard up against its housing. Unfortunately, I had cut so much away that I couldn't drift out the remainder from the other end from which the bearing had been removed, as there was nothing left for the drift to make sufficient contact with. In the end I ended up making a series of vertical cuts with the Dremel in the hope of being able to prise a tiny section of the outer ring of the bearing out without doing any damage. To say this is not easy is an understatement, but eventually I was able to get a bit out, and from there to lever out the rest of the ring. Inevitably there was a bit of damage, but in the circumstances, not much - a couple of nicks in the shoulder of the tube, which shouldn't have any effect on the efficiency of the new bearing. The moral is, pull out a bearing if you possibly can. Good luck with that. You're going to have to fabricate some kind of special tool. Failing that, I would suggest using a metal punch narrow enough to pass through the hole in the bearing and long enough to reach the bit of the bearing at the other end which sticks up above the shoulder, and to tap gently, working on opposite sides of the bearing alternately to see if you can get it to move without jamming it. If it doesn't work, see if you can get the other bearing out from the other end by the same method; again try to prevent the bearing from twisting. Once you've got one bearing out, the second is easy. Bon courage.

 

The bearings can be steep to buy or hard to find. But I got some off of McMaster-Carr for very little.

 

Thank you for the info. KMX have offered to sell me a set, so that will be my first course of action. If that fails for some reason, I'll follow up your contact, and keep it in mind for the future. Best wishes.

 

I obtained two sets of new bearings from KMX in case I have to change the set on the other front wheel. Putting the new bearings in was easy. I started with the inner bearing, and knocked it in flush using a wooden drift and many little taps going round the rim of the bearing, checking constantly that the bearing was going in evenly. I then followed up a tip from KMX, and mounted the wheel on the axle using the single bearing, and used the axle nut and washer to wind in the new bearing. You have to guess when the outer bearing is seated against the shoulder. If the axle nut suddenly becomes hard to turn you're probably there, and you need to back the nut off a little until the wheel runs freely. It all seems fine now.
If I have to remove the bearings again, I intend to use 3 or 4 metal tent skewers. I shall cut the bent bit of each peg right back almost to the main body of the peg, leaving just enough to catch on the inside of the bearing. My plan is to feed the skewers one at a time through the hole in the bearing, ensure that they are turned in such a way as to catch the edge of the bearing as mentioned, feed an extra spacer into the middle as or if necessary, then find some way of binding the whole bundle together and try to pull the bearing out like that . Another possibility is to use a commercial expansion bolt to grip the inner ring of the bearing. This would probably be a better solution if a suitable product could be found, and certainly less fiddly.

 

Hello, once again. I hope this will be my final and definitive post on the replacement of KMX Cobra front wheel bearings. You read above of my trials and tribulations changing the bearings of the offside front wheel. This was done as part of the preparation for a tour of Brittany cycle paths. I have now returned from this - about 500 miles - and the new bearings behaved impeccably. However, it became evident that the nearside wheel bearings were also starting to creak and need replacement. I wasn't looking forward to doing the job again, but in fact, I did both bearings in less than an hour total, with little difficulty. The trike is 10 years old, and I must stress that you should check with KMX that the design has not changed in that time - but assuming it hasn't, here's how to do it. Remove the disc brake from the wheel in question, take the wheel off, then take off the brake disc so it doesn't get damaged in subsequent operations. As mentioned above, the inner bearing is flush and the outer bearing recessed. It's easier to remove the inner bearing first. I sprayed both bearings with WD40 and left the wheel for a while, but even so it took a bit of effort to knock the first bearing out. Contrary to what I thought when I didn't know quite how it was all put together, you can knock the inner bearing out with a drift from the other end. You need the widest steel rod that you can pass through the hole in the outer bearing; I used a drill bit partly inserted into a wooden block on the end that was going to be hammered. Push it through until it makes contact with the inner edge of the inner bearing, which does stick up above the shoulder enough to enable you to start tapping the bearing out. You can't just whack it wildly or you will skew it horribly in the bearing recess. You need to angle the drift and knock the bearing out, top, bottom, left side, right side and repeat, constantly turning the wheel over to check if the bearing is moving, gradually increasing the strength of the blows if necessary until you see evidence of movement, always being careful however not to skew the bearing. Once it comes out, you can use a bigger, wooden drift to knock out the other bearing; I used a bit of old broomstick. This is a much easier proposition. You can use a wooden block and a hammer to carefully knock the new inner bearing into its housing, as gently as possible so as not to damage it. Then put the brake disc back on the wheel and mount the wheel on its axle. Place the new outer bearing on the axle and tighten the axle nut thus pushing the bearing evenly into its housing. Once the bearing is properly seated in its housing, you can back the axle nut off slightly; it does not need to be very tight, but since there is no lock nut, I put Loctite on the threads to prevent any possible movement. All that remains is to refit the disc brake and adjust it if necessary. I feel much more confident about doing the job now, and I intend to change the bearings after a considerably shorter interval than 10 years in the future as part of a general maintenance schedule. I hope this will be useful to anyone else attempting to do the same job. Good luck.

 

Thank you for the explanation of the process. I have a KMX but it is not a cobra. Mileage is approaching a point that I may need this information in the near future. So I thank you in advance for such a detailed explanation of this process.

 

flypaca 1. I hope any bearing change you do goes well. KMX have a reputation for being helpful when you contact them. They sell bearing packs at a price which, even allowing for international postage, is probably hard to beat. I think I paid under 12 pounds sterling including UK postage for all 4 bearings to service the two front wheels. At that price you can do them every couple of years or so. Good luck!