New axle bearings staying tight - how to free up?

This year I put new axle bearings in my sons kid kart as well as my own chassis. In the past I’ve noticed that new axle bearings can be tight and have extra resistance, but typically loosen up after a few sessions on track. My new bearings behaved exactly like this.

My sons 25mm bearings in his kid kart don’t seem to be breaking in even after 5+ sessions on track. The bearings have been lubed with tri-flow for each run and I’ve used brake cleaner and air to blast out the bearings and then re-lube. This helped a bit but they still have noticeably more resistance than the old bearings to the point I’m considering putting the old bearings back in.

The bearings are standard axle bearings, no ceramic or polished/treatment on them. I’ve also verified the axle is installed appropriately, not bent, and not binding.

Is there something else I can do to help loosen the new bearings? Or since the forces are so much less in the kid kart are they just going to take much longer to free up? Could there be something wrong with them?

I found some reprieve in that I had the pinch bolts in the bearing cassettes pretty tight. When I loosen them the bearings spin more freely. It’s still not where I think they should be though, and I’m considering putting the old ones back in. Anything else I might be over-looking?

Could it be the bearings are slightly cocked in the chassis or something? If loosening the pinch bolts helped, it seems like the bearings could be slightly cocked.

I’ve had that happen and it was misaligned. Loosen set screws loosen cassette bolts then I moved the axle back and forth, gave it a good shake then slowly tightened the cassette to chassis bolts back and forth. Spin axle, get it in place then tighten set screws. Also, not sure if it’s the correct way but I didn’t cassette conch bolt all the way. I tighten it maybe half way.

Thank you for the advice. I’ll check the axle and bearings for alignment again.

For clarification on axle install: I start with the pinch bolts out and cassette bolts loose. I’m sliding the axle through the right side bearing and adjusting it so that it will line up with the lefty side bearing and slide in without additional effort. Then I remove the axle and do the same on the opposite side. Then I center the axle and install the axle set screws. Then I tighten the cassette bolts and pinch bolts. Am I missing anything there or doing anything out of order/wrong?

Then I center the axle and install the axle set screws. Then I tighten the cassette bolts and pinch bolts

Tighten the axle set screws last.

I tighten the cassette bolts first. Since when you do it sucks the cassette up the the frame. If you tighten the axle set screws first then the cassette to the frame it could put some weird binding on the axle. So my order of tightening is cassette to frame them axle set screws the punch bolts. But like I said I prefer only to tighten pinch bolts just barely snug. Just enough so they don’t back out and you lose them.

Thank you for the clarification. I’ll check the axle before our race this weekend.

As a follow up it must be a problem with the bearings. I removed them and tried soaking in oil and heating but still tight. Axle was not binding and slid out easily. I put the old bearings back in and despite sounding a little crunchy they are a 10x reduction in rolling resistance.

Haven’t had time to mess with the new bearings to see if the shields are touching the collar or something like that.

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