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
What's this?
It is a JIS square tapered BB. And in english...
BB - bottombracket. Screwed into the frame and serves as a mounting point for your cranks.
Square taper - Axle shaft of the bottombracket is tapered. The shaft is wider at the base than it is at the tip, so it ensures a very tight fit when the crank is tightened up. It fits square holed cranks only.
JIS - Japanese International Standard. This is a measure of the degree of taper. There is also the ISO standard used by European manufacturers, such as Campagnola. The vast majority of mountain bike cranks are JIS. An ISO crank may or may not fit a JIS square taper BB depending on the tolerances and amount of wear.
Evolution or Devolution?
In the last few years BB's have undergone something of a revolution. Octalink from Shimano, ISIS from ...
'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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