Bicycle Mechanics - try again: reverse/normal Shimano sealed BB
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11-28-06, 12:41 PM
My thread seems to have been deleted, again sorry if this is now old news and redundant...I pulled a cheap sealed Shimano BB unit out of a Trek 860 Mtn. bike (maybe a mid '90s)and discovered it was the OPPOSITE of a normal BSC threading pattern. The drive side is RH threading and the black resin cup non-drive side is LH thread. I think it is stamped LN26, but don't have it in front of me so could be wrong...it's NOT a UN series, is a gray metal body with square taper spindle. This is the second unit I've come across like this, the other being an older Trek, too, but a road bike. Any help appreciated, and thanks to the guy who already responded to my first post asking about the number...i'll know for sure in a few days when I get back to the shed.
11-28-06, 01:54 PM
I tried responding to this yesterday. I have one of these BB's in my bike (68mm shell, british). Basically, this bottom bracket had the flange (the "fixed" cup) on the left hand side of the frame. I believe shimano probably did this to save on tooling, as the left cup has normal threads. The reverse threaded cup was plastic.
Anyway, you can replace it with a regular square taper BB. Your bike won't be able to tell the difference.
11-28-06, 04:15 PM
The low end shimanos (CS,LP) are "reversed" in that the fixed cup goes on the left side (right hand thread). All the UN bottom brackets have fixed on the right side (Left Hand thread).
You have to be careful because the plastic cup, if installed on the wrong side will have threads = toasted.
11-28-06, 05:14 PM
Thanks, I guess that explains it, I just haven't had much exposure to the cheap-ass end of Shimano. Looks like I'll have to replace with an equally cheap BB unit or do it "backwards" with a better one.
11-28-06, 05:48 PM
I wouldn't worry about it too much. The cheaper ones allow the bearings to be serviced while none of the UN series do. However an LX quality UN bb is only like 20 bucks.
11-28-06, 06:34 PM
You can press out the bearings in the cheepos? Is this an obvious procedure (with a vise and handtools) or is it not worth the hassle and/or requires special tools? Even with the low cost of the lowest UN, I'd rather press in new cartridges, if easy, cause I know this unit fits the frame and the crank it came with.
11-28-06, 08:32 PM
Technically you can, with the Park BBT-6. But no one ever does it cause the tool costs like $200. Anyways, what I meant was that you CAN lift a seal and flush the solvent out and regrease the bearings. But not "adjust" them in the traditional sense as with cup&cones.
11-28-06, 10:41 PM
understood...and thanks again to you and all.
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