Press-fit Cartridge Wheel Bearings

Joined
Jun 4, 2003
Messages
2,014
Location
98245
So while I was rebuilding my hub (broken axle, worn freehub pawls), I figured I might as well put in new bearings (size 6902). I ordered a pair of NSK bearings, which are supposed to be excellent. I cleaned out the rat piss they use for OEM grease and lubed it up with Schaeffer's 221 #2. They were butter smooth. Then when I pressed them into the hub, they were not only high friction, but rough. I pressed them back out and they were butter smooth again. I went to the LBS and bought a set of generic 6902 bearings, same procedure, butter smooth when installed in the hub.

So apparently, the compression/squeeze forces of being installed in the hub caused NSK bearings to rub & stick? That's the only plausible explanation I can imagine. Maybe the hub bearing socket was not perfectly round, but seems unlikely since other bearings are butter smooth as installed.

Have any of you experienced a perfectly smooth new bearing becoming rough when installed? I mean properly installed with a good smooth press, not whacked into place.
 
A lower pivot bearing on my Ghost SLAMR
X (full suspension trail bike) did this on one side.

Took the whole bike apart at the end of a season to paint and overhaul and found the bearing notchy. Bought new bearings, installed them and the new bearing was also notchy. Pressed it back out and it was smooth. I ended-up sanding the hole a fraction of a millimeter larger and that totally fixed it. Ghost sent another chainstay also, so I have a backup.

I was able to measure the hole with a digital caliper and you could tell it wasn’t perfectly round. I forget what the measurements were, but it definitely wasn’t perfectly round.

7741743B-E6A6-4ED5-943E-62A39F5EEED5.jpeg
 
... Bought new bearings, installed them and the new bearing was also notchy. Pressed it back out and it was smooth. ... I was able to measure the hole with a digital caliper and you could tell it wasn’t perfectly round. ...
Sure, an imperfectly round bearing socket will definitely do that. Kudos for your fix! I doubt this is happening in my case, since 2 other bearings are butter-smooth when installed. It was only the new NSK that got notchy when installed.

I wonder if non-caged bearings are more tolerant of imperfectly round sockets? Seems they might be.
 
Couple quick comments as a former Timken engineer...

Yes, if you have too much interference fit during installation, you can "tighten" the clearance of the bearing to the point of binding. In an ideal situation, you would measure your housing, measure your OD, and do a quick calculation as outlined in the bearing manual to understand if you are in spec or not.

Did you press the NSK bearing back out, re-clean, and re-install? Perhaps there was debris in between your press fitting that changed the fit?

Slightly tight bearings will actually live longer, as they spread the load over a larger area of the inner race (load zone). If they were gritty, it means you had contamination, but if they just felt a little tight, it may have been just right for overall life and performance.
 
Couple quick comments as a former Timken engineer...

Yes, if you have too much interference fit during installation, you can "tighten" the clearance of the bearing to the point of binding. In an ideal situation, you would measure your housing, measure your OD, and do a quick calculation as outlined in the bearing manual to understand if you are in spec or not.

Did you press the NSK bearing back out, re-clean, and re-install? Perhaps there was debris in between your press fitting that changed the fit?

Slightly tight bearings will actually live longer, as they spread the load over a larger area of the inner race (load zone). If they were gritty, it means you had contamination, but if they just felt a little tight, it may have been just right for overall life and performance.
In a word, yes. The NSK bearing after install was not only sluggish, but notchy. I pressed it back out, butter smooth. Pressed it back in, sluggish and notchy.

I always scrupulous clean the hub seat and bearing and use a smidge of grease in the hub seat to ease fitting. Two other brands of 6902 bearings (one caged, one non-caged), no problem. Butter smooth when installed in the same hub socket. Perhaps this particular hub socket is on the tight side of allowable tolerance. Or is slightly out of round and the NSK bearing is more sensitive to that.

By comparison, the bearings on our tandem, both bottom brackets and the wheels, have always been sluggish/high friction yet butter smooth. 20,000 miles still rolling like new. I always assumed that was a sign of a heavy duty bearing (like a car or motorbike bearing), and due to the more viscous grease used, which has higher film strength to better prevent metal-metal contact. But maybe it is due to being on the tight side.
 
It could be that it's on the tight side, more likely that it's not round.

I build a lot of bikes including custom frames and hubs. I have run into this issue when pressing bearings into tubing which is distorted. The bearing itself is not structural. It's designed to be pressed into a bore which is round and provides strength. Even if it's not a hard press fit, if the bore isn't round the bearing doesn't run well. In contrast, you can press the bearing into a ROUND bearing seat with a very tight fit, and it will run fine.

A potential fix is to ream out the bearing seat to a looser fit, then re-install the bearing with a retaining compound.

Another is to install a beefy steel sleeve, and re-ream it to round but that's precision machining probably not suited for a bicycle.
 
Yep. All dimensions appear exactly the same to the eye and hand, and they measure the same with my caliper. Though, they could be off by a few thousands and I wouldn't know, and that might be enough to explain the tightness.
Either way, I have a bearing in there now that is perfectly smooth, so it's all good.
 
Back
Top