I have had three or four of these because they were cheap, it turned out that in the long run it was cheaper to save up and buy a decent bottombracket. Everyone of these that I bought broke in under a month, the same two faults occured each time. 1) Mud and grit easily get past the seals and wear out the bearings causing them to cease or rattle. 2) The ends of the tapered arms round off very easily, even during light XC and commuting use I have rounded them off. Steer clear and buy a decent bottombracket, or even better get the new external type, or if your into jumping and DH get some 3piece cranks. ...
Advantages: Cheap, extremely durable, abuse tolerant Disadvantages: Poor crank choice, may not be suitble for extreme use
the others, and now the latest big thing are external bottombrackets. X-type from Race Face, Hollowtech II from Shimano, and GXP from Truvativ. While they have different names they are all interchangeable, as they are all made to similar specifications and similar dimensions.
Each "improvement" has led to stiffer and lighter BB's, with a marked decrease in durability. The latest BB's can last as little as 3 months on a mountain bike, if ridden in wet and muddy conditions. ISIS are particularly bad in this regard, but the new external BB's are in a class all of their own. Mounting the BB outside of the frame, makes them extremely vulnerable to water penetration and early failure.
The UN54 will give you an average service life of around 18 months to 2 years, and this reason alone may be enough to persuade you to stick with square taper. My ...
't know, take the old one to the bike shop with you. If you're having the job done for you, then the shop will figure it out for themselves. The new one will be a silver cylinder (as opposed to the brownish rusty cylinder that's just come out of your bike) with an axle poking out of both ends. This then screws into your frame with a little dab of grease on the threads using the aforementioned bottombracket tool. Cranks sit on the end of the bottombracket and the bolts that you took out earlier can be screwed back in. All in all, a fairly simple (but messy) job, although the fact that you have to spend more on tools to do it than the cost of parts may well force many peoples' hands in deciding to get a bike shop to do it.
So, now that it's fitted, what difference are you going to notice? Well, in my case the first UN72 I fitted was to ...
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