UN300 - less than 300 miles and it's toast

[Ugo51]

Hi guys,

I just wanted to report my latest encounter with a defective bottom bracket. I purchased a Shimano UN300 for my Boardman and installed it just before going back home for the Xmas holidays. I did about 150miles before the holidays and 150miles since I am back. This morning I noticed the non-drive side bearings are loose. I haven't taken the BB off yet - will do tonight - but it seems the bearing are toast.
Very strange.
I will (hopefully) know more once I examine it, but I am very surprised about this.
Of note, I recently purchase another UN300 and it looks quite different from that one I bought in December, so I am starting to suspect one or the other is not a UN300...

Will keep you posted.

 

[Tootyred]

Thats interesting to hear.

I trashed a un300 last year, its the first shimano bb ive ever had go so quickly.....from fine to wobbling about in one ride. It was second had, but was said to have done less than 50 miles......it certainly looked like new and to be honest it was so cheap I'm not complaining!

The drive side bearings went wobbly on me after about 500 miles. Originally i thought it might have done more than the owner had said, but im now starting to wonder....

I thought it had come loose to start with, but the movement was rubbing the chain on the front mech. When i took it out the drive side bearing had movement in it.

 

[Woz]

It's a sad state of affairs. Have in mind, for about 20+ years Shimano is not offering any decent square taper crank, and I suspect these UN300 are intended to be matched to very low end dross like Tourney or whatever.

 

[Jamesbike]

Any recommendations for a quality square taper BB??

Not that I need one ATM.

 

[Jamesbike]

https://forum.cyclinguk.org/viewtopic.php?t=6268412 pages of advice here....

 

[Woz]

https://forum.cyclinguk.org/viewtopic.php?t=6268412 pages of advice here....

.....and those threads are 10 years old. Without going into Royce and Phil Wood territory:

Concerning Shimano, it's best to get some NOS or very good condition UN7x or UN5x, stock up when you can.

Tange and Token still make quality BBs:
https://www.tokenproducts.com/bottom-brackets/threaded/jis-square-taper-1

Stronglight JP400 is popular with industrial cartridge bearings, but a few notes:
- Older models seem better quality, perhaps those made in France many moons ago.
- I took a fairly recent one to pieces and found it was actually a NECO which seem to have a decent product line and available cheap.
https://www.necoparts.com/en/category/Cartridge-Cotterless-Bottom-Brackets-Sets/A0201.html

 

[Tootyred]

Im running 2 400 stronglights both doing well at the moment and cheap to boot.

 

[Jonny69]

Good to know this about the new UN300. I’d better hoard my two UN55s.

Those cheap Neco square tapers with the alu cups and hollow axle are surprisingly good. I put 11k miles on the last one on my fixed gear bike before the bearings needed changing. You can tap them apart, too, so theoretically you could replace just the bearings.

 

[Ugo51]

I honestly think this was a bad copy. I refuse to believe the overall quality of the UN300 is so low they only last a few hundred miles.
I installed a new one and took the occasion to put back the 170mm cranks. Let's see how long it will last for...

 

[CassidyAce]

+1 for the Neco BBs. I put a cheap one in my commuter and, three years later, it's still riding as it was when new. No long mile-munching rides but lots of short journeys through all weathers (rain, snow, even sunshine!) and a fair dose of sea air.