Needle bearing Play

[Feanor]

Even though I think I waited a bit too long, this last weekend with about 5 or 6 rides on the KDX-220 I tore down the rear suspension (shock mounts, dogbones, swingarm, shock pivot) cleaned and regreased every needle bearing.

Apart from re-using the old cotter pin on the rear wheel axle, everything went smoothly and by the numbers.

I did, however, run into something very very curious...

on the shock pivot piece, the pivot part that actuates the rear shock via the dogbones, I noted that there was ALOT of play between the bearing race (the steel cylinder that runs inside the needle bearings that you normally slip out to regrease) and the pivot bolt, that goes thru the steel cylinder...

Hmm, this is not clear enough... hopefully this is clearer... When you insert the pivot bolts thru the "sleeves" the bolts rattles around alot in the sleeve and are not even close to a nice slip fit... (the main swingarm bolts and bearing are a much closer tolerance, but almost all the pivot bolts fit in the dogbone assembly very loose...

My bike is still brand new with NO hard riding on it at all prior to this disassembly...

Is the tolerance in this area of the suspension supposed to be this sloppy? Without measuring, I'm gauging that if the inside diameter of the bearing sleeve is 12mm then it feels like the bolt that goes thru it has an outside diameter of 11mm it feels that "sloppy" :(

Kind of defeats the purpose of bearings when the pivot rattles around doesn't it?

Thanks in advance for any info...

Feanor

 

[canyncarvr]

You are referring to the Unitrack I presume?

You are referring to the bottom shock mount (part of the Unitrack) I further presume?

You are correct. Nowhere's near a mm of play...but way more than you would think reasonable.

Take a look at the bearing that sleeve rides in. It's worse! Looks like it's missing a needle it's so sloppy. The needles IN the bearing aren't even straight 'fer crine' out loud!

And not a one of the 1/2 dozen or so I've bought look any different. And NEITHER have I found a replacement bearing from some real bearing mfg. No one has been able to match the spec.

'Kind of defeats the purpose of bearings when the pivot rattles around doesn't it?'

It would seem so.

SO....when you get a good replacement piece, a teflon or spherical bushing or whatever...please let everyone know! ;)

 

[Feanor]

Thanks for the info...

Thanks for the reply Canyncrvr,

I just wanted to confirm that I either wasn't crazy, or didn't have a bike built on Friday afternoon by someone who reported to work sick :)

With so much slop between the pivot bolt and the sleeve it rides in, I would be surprised if the bearing did more than half the rotating as the pivot just rocked "to and fro" inside...

Additionally, since the pivot bolt does not have a more precise fit in the sleeve, under load, the force is focused on a small part of the sleeve and not distributed across a larger surface area (think of a placing a broomstick in a large pipe and lifting up as an extreme analogy) which is the whole reason for utilizing needle bearings in the first place!

All of this analyzing on my part may just be purely academic. I mean, the KDX has been around a LONG time and has earned a reputation of reliability and effectiveness. I would assume this is true even WITH the slop in the unitrack bearings, so maybe the wiggle room serves some valuable purpose that I'm simply missing... Maybe the slop is required to reduce stress on the parts, and if the pivots were a tighter tolerance the unitrack would overstress and fail at some point... Who knows?

The only thing that confuses me is that all that slop in there runs contradictory to even having bearings in the first place and they might even make the KDX more attractively priced if they used far cheaper alternatives like bronze bushings...

I have a friend who works in a machine shop and regularly turns delrin and urethane bushings for car suspension modifications... I'm going to draft up some mechnical drawings and have him make me some thin delrin inserts that fit around the pivot bolts and give them a nice tight press fit into the bearing sleeve. That should get the bearings working 100% of the time and also provide a nice protection against shock loads...

I doubt if I will feel any performance/handling difference, but at least I'll know the the unitrack is nice and tight, and the bearings aren't getting "peened" every time I hit a rock :)

Have a good one!

Feanor

 

[canyncarvr]

Why not just replace the whole mess?

What are the +/- of having something like a urethane or Delrin bushing fit into the Unitrack that replaces the bearing?

There has been some discussion in the past as to which would be best:

1. A bushing that replaces the bearing...use the oem sleeve/bolt.
2. A bushing that replaces both the bearing AND the sleeve...use the oem bolt.

There are advantages to using a sleeve...but you have a thinner bushing.
There are advantages to using a thicker bushing, but then you have direct bolt contact.

If you come up with something that you think works, please drop me a line. I'd sure be willing to contribute to the project.

Good luck!

 

[JasonWho]

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[canyncarvr]

Solid. Not threaded.

Are there applications (model years for example) that have the threaded part of a bolt riding in a sleeve? That would be hokey.

Doesn't mean it doesn't happen.

I've meant to spend some time researching different bushings for that spot (lower shock mount). I haven't pursued it to actually having something to put IN the Unitrack.

 

[Feanor]

Why not just replace the whole mess?

If you come up with something that you think works, please drop me a line. I'd sure be willing to contribute to the project.

Good luck!

I'm going to talk to my friend this weekend about it... I explained it a little on the phone and he wants to get a closer look at the assembly... His recommendation was to simply (heh, simply for HIM) turn a new pivot shaft that was a slip fit replacement of the OEM shaft/bolt... He told me if I paid for the raw material he would even turn it out of titanium for me! *laughing* Not sure I want to go that overboard :)

He did actually ask wether or not I knew if the "slop" was purposely engineered into the design and of that I have no idea, but he was of the same mind as me and mentioned if they were using roller type bearings that would normally indicate some fairly close tolerances...

I'll keep you posted...

Feanor

 

[Feanor]

Solid. Not threaded.

Are there applications (model years for example) that have the threaded part of a bolt riding in a sleeve? That would be hokey.

Doesn't mean it doesn't happen.

I've run into many instances where this happens (thread part of the bolt running in the sleeve, but nothing on as grand a scale as in a motorcycle suspension.

I fly RC helicopters and sleeve/bearing and screw pivot shaft is a very common design implementation... In the case of the model helicopter application, it is actually required to apply threadlock to the portion of the threads that come in contact with the inside of the sleeve. This is done to ensure that the sleeve rotates within the bearings and that the screw does not simply rotate inside the sleeve, causing excessive wear, increased friction and obviating the need to even have bearings! :)

That's why I thought it odd when a friend told me to apply grease to the outside of the bolt to help prevent the bolt getting frozen into the sleeve, I almost wanted the bolt to get fixed in there to make sure the bearing was doing ALL of the work :) Otherwise its all just a really expensive and complicated bushing :)

 

[canyncarvr]

re: grease the bolt.

Yeah...it's the sleeve/bearing joint that is supposed to be doing the work...but when you're dealing with something like a dirtbike suspension that just might be subjected to some nasty conditions, having the bolt corroded to the sleeve makes it a bit difficult to remove sometimes! ;)

You've likely read of riders spending days with penetrating solvents, heat AND sledges trying to get the swingarm pivot bolt out. I doubt they thought, 'Gee! I'm glad the bearing action isn't taking place between my sleeve(s) and the bolt!'

re: 'His recommendation was to simply (heh, simply for HIM) turn a new pivot shaft that was a slip fit replacement of the OEM shaft/bolt'

That isn't going to resolve the problem of the junk bearing. A 'proper' fit between the bolt and sleeve isn't going to make the bearing live any longer...the fact that the bearing itself is junk notwithstanding!

Ask him (simple for him?, you bet!) to get RID of the bearing with something else suitable. If that includes making the sleeve/bolt fit better, so be it.

Yes...I have replaced the seals when I've replaced the bearing. I've also re-used old seals. I didn't note any difference in bearing life. What did make a difference in bearing life was the use of some killer grease (the Hydrosyn-70 stuff).

The bearing is still junk...AND the other parts fit just as well.

Is such slop a design feature? Not in any way I understand the application.

***edit***
I don't understand 'roller' to be the same as 'needle'. I would say there are 'roller' bearings in the wheels...but 'needle' bearings in the suspension.

Well..until you help us out getting rid of the dang thing!!

 

[Feanor]

Ask him (simple for him?, you bet!) to get RID of the bearing with something else suitable. If that includes making the sleeve/bolt fit better, so be it.

The bearing is still junk...AND the other parts fit just as well.

Is such slop a design feature? Not in any way I understand the application.

***edit***
I don't understand 'roller' to be the same as 'needle'. I would say there are 'roller' bearings in the wheels...but 'needle' bearings in the suspension.

Well..until you help us out getting rid of the dang thing!!

Sorry about the confusion with the needle bearing Roller bearing nomenclature that always gets me confused... From now on I'll just say the unitrack bearings :)

My friend was working on an anti roll bar suspension mod several years back where the bar (which was large diameter and hollow) attachment points to the frame of the car were bearing housings and the bar rotated in these bearings instead of the typical urethane bushings. It was a very cool looking setup... He was saying that the bearings avoided the "stick-tion" normally associated with the inexpensive compromise solution of the bushings anti-roll bars are normally "clamped" into...

From my memory, the bearings were much larger than the largest bearings being used in the Unitrack, and he did mention that they were quite expensive, so I'll definitely ask him about possibly finding a place that might carry high quality bearings replacements for the OEM stuff in Unitrack...

 

[JasonWho]

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