Thread: Shot in the dark... Bearing problem/question - long post

My RMX has been on the fritz recently and it's popping seals out of the bearings on the pivots. At $25 a bearing, replacing them every ride is getting old quickly, but putting it on ebay with the problem is a bit shady. There's a bunch of smart people here, so I figure someone should be able to tell me something I don't know about this...

Here's a picture of what's happening (I have the suspension taken apart).



Here's what it should look like (sorry for the blur).



I have have a few theories and am looking for someone else's opinion on them or maybe something I haven't thought of. I'm used to just seeing bearings break, not just having the seals come out.

1. I'm overtightening the bolt through the pivot and somehow squishing the seal. The pivot has two caps on either end and a big bushing through the center. The bushing is not as wide as the whole pivot, so there's a little gap (maybe 3-4mm) that ends up in between the cap for the nut side and the bushing. Is it possible that when I'm tightening the bolt, I'm pulling the center race over enough to damage the seal. The last time I put it together, I noticed grease coming out of the bearing after a run, so it appears that damage during assembly is possible. But, it also seems like the bearing should be able to take the force of me tightening it down.

So what do I do to fix this? Shim between the cap and the bushing? I'm a bit scared to do that because I'm worried about not being able to tighten everything up enough (ie now I don't have enough pressure on the bearing).

2. I'm just that hard on the bike that everything is flexing enough to dislodge the seal. This seems highly unlikely to me and should to anyone who has ever ridden with me. The biggest thing I hit this weekend was maybe 7 or 8 feet at the most and everything I did hit had a transition. I remember bottoming the bike out twice this weekend, but neither time was around the time that the seal came out.

3. Linkage is damaged and is causing the problem. This too seems unlikely, as it's a big piece of machined aluminum. I suppose the hole for the bearing could be slightly off, but based on other bikes I've seen, things like this seem to end in catastophic failure.

4. The bearing fairy or some sort of woodland creature is fucking with my bike when I stop.


Edit - Complicating this whole deal is that I can't find a number/email for Rocky Mountain and the nearest dealer is 1.5 hrs away... Also, I should note that the bearing is a 3804-2RS, it's dual row bearing and is pretty heavy duty.

I'll go with the fairy concept.

Actually what you might try is go to Brewster and on Rt 6 just before the Connecticut border on the left is Dalc Gear and Bearing. Have them hook you up with some real bearings, not that crap with nylon seals. If there aren't higher grade bearings available they should at least be cheaper than what you're paying now.

check the frame/linkage for bends. make sure everything lines up right.

http://bikes.com/about/contact.aspx

To contact Rocky Mountain Bicycles, please write or call us at:

Rocky Mountain Bicycles
1322 Cliveden Ave.
Delta BC Canada
V3M 6G4

Phone: (604) 527-9993
Fax: (604) 527-9977

At Rocky Mountain Bicycles we stand behind every bike we build. If anything goes wrong with your bike, contact ANY authorized Rocky Mountain Bicycles dealer in your area. To locate your closest ROCKY MOUNTAIN® dealer, you can check the dealer listing on the website, log on to www.bikes.com or call our Customer Service department at (604) 527-9993 or fax at (604) 527-9977

Downhill and Freeride: 3 Years - limited* Hardware, suspension pivots and bushings, 6 months.

Thanks mtnlion... Not sure how I missed that info.

First a quick lesson about bearing terminology.
The outer peice of metal is the outer race.
The sleeve where the bolt runs through is the inner race.
The plastic thingy that keeps coming off is just a dust seal.
anyway now that we have that done here are thoughts in order of theories.

1. If you tighten a bolt too much that runs through the inner race of the bearing, you will physically deform the race enough to make it bulge. I know it doesnt seem like it, or that you would be able to make it physically move enough, but we are talking about bearings here. Tolerances are commonly kept to .0001" on the sphericity of the ball bearings themselves. Go easy on torquing them. Snug plus a half or something. Or get a torque wrench out and torque it to something like 40-60in-lbs for what size bolt that looks like. Put some loctite on there if you're worried about it vibing loose.

If you can find a shim the right thickness, it will probably be too thin (by looks of it from the pics) to create any significant load bearing capabilities. It will instead act like a secondary dust seal which might be beneficial in this case. I would maybe even sugguest just finding a nylon\plastic washer to do the same thing with. In this case the nylon would deform enough that it wouldnt matter if there was a cap, cause you would just crush the washer anyway. Go back and check torque after a couple of hours.

Also it worth nothing that so long as you have the proper press fit into that link pivot, having the bolt super tight will only incur extra friction and resistance due to the race deformation I pointed out earlier. The link also sees no substantial side loading, and as thus, isnt really critical for having a bearing walk out of its press...again assuming its a good press fit.


2. I doubt its you being too ahrd on the bearings. First thing to remember is that the dust seal is a crappy peice of plastic. Second thing is that maybe you are tighting down on the inner race too much.
Third thing is to add a cheap nylon washer as discussed previously. Popping out a dust cap will not ruin a bearing. Also Id suggest you just clean up the old bearings you have unless they make horrid clicking and binding noises when you try to turn them by hand. Repack them with grease and you're ready to go (with the addition of a nylon washer as mentioned)

3. I would say its definitely worth inspecting your pivot bolts to verify they arent bent. Chance of the aluminum peices being bent is pretty slim, but worth checking with a steel straight edge. My concern would be the press fit. If the bearings slide in too easily, thats not good. That will not support the bearing and actually create an impact loading to the bearing. Also verify that you ARE NOT HAMMERING them in when you are installing them. You want to gently press them in. In this case, just use a bolt and nut to tighten them in there. Bearings DO NOT like impacts.

4. the bearing fairy is a big hairy lumberjack and could destroy your bike, but hes generally nice and sedated off his homebrew moonshine.


To clarify, how are the bearings breaking?

Originally Posted by pechelman

2. I doubt its you being too ahrd on the bearings. First thing to remember is that the dust seal is a crappy peice of plastic....Popping out a dust cap will not ruin a bearing.

I know and the bearings aren't breaking. The problem is that since they are not MAX bearings (and I can't seem to find any that are), there is a retainer under the seal that spaces all the balls. Once the seal comes out, I lose the retainer and the balls clump to one side. Once the seals come out, I just pack it full of grease and put duct tape over it for the rest of the day. Being realistic, there's only room for maybe another 4 balls in there, so I highly doubt the bearing will break, but it's always in the back of my mind. Also, the bearings have two rows of balls in them, so I'm probably not losing much with the one clumped side.

Originally Posted by pechelman

My concern would be the press fit. If the bearings slide in too easily, thats not good. That will not support the bearing and actually create an impact loading to the bearing. Also verify that you ARE NOT HAMMERING them in when you are installing them. You want to gently press them in. In this case, just use a bolt and nut to tighten them in there. Bearings DO NOT like impacts.

The bearings are going in using a vise, so I'm essentially pressing them in.

To clairfy how it's 'breaking'. I'm just getting to the bottom of a run and noticing that the seal is missing or that it's coming out. After writing this all and thinking about it, I'm pretty sure that this is a case of me overtightening things. I noticed grease (it was white, my grease is green) coming from the inside of the seal Saturday morning, I'm guessing this is because I moved the inner race enough to screw up the seal.

The fact that the bearing/bushing sleeve between the two cartridge bearings isn't contacting the inner race of the two bearings on each side is a little wierd. That thing is there to allow you to tighten it down pretty hard without pushing the inner race in further than where the outer race is seated in the frame/linkage/swingarm or whateve it sits in.

Get ahold of rocky and some calipers and see if its the right length. You might also not be getting a good seat due to thick paint or poor alignment.

And like mtlion said, make sure everything is straight. I'd take the shock off, unbolt the linkage and see if it swings together symetrically.

You could be getting some flex from the main pivot or elswhere that's over sideloading these things and making them twist. I'd go through each pivot, main and linkages, one at a time and see if you can get them to twist independently.

Rocky machines most of their stuff in house and from what I've seen, usually do a pretty good job of it but you may have something crooked too.

Lots of stuff to check but you start narrowing things down. BTI and/or QBP big distributor/wholesalers should have enduro max bearings that a decent bike shop could order for you for future reference.

Good luck