Square tapered Bottom brackets
 

Greetings all

I have been reading bike forums posts for years, but today I finally created a profile. In honesty, I need a little help...

I ride fixed gear, and i have a pretty cool bike. I use all city 612 cranks on my bike, and well, as a heavier rider who puts a lot of miles on, I have began to wear down and strip the square taper. I have read a lot of interesting stuff, mostly from these forums, about what made that happen. In a nut shell, what I have learned is that I should have known about all city's torque specs before I put them on last august. My cranks have been coming loose the entire time I have had them. I would always just tighten them back down but never to a specific torque. Does anyone know all city"s torque specs? I have looked on their website, but it does not list them.

I like the options for color you get from square taper cranksets, there seems to be more, but I need suggestions for a new square taper crankset, or I am going to have to do the whole splined thing. :/

I really liked my all city cranks, when they worked right, they worked well. I just don't want to spend another 135 bucks on them if this is what I have to expect.

Also, if anyone wants to offer me advice or knowledge I may not know about the workings of square tapered crank sets and bb's, let me know. I've only started getting to the maintenance side of biking last summer.

for sq taper cranks 30 ft lb is good.

Square taper is alive and well. If torqued properly, they should be fine. The problem you encountered was due to incorrect installation not a problem with the square taper interface.

I've never used a torque wrench and have several bikes with ST bottom brackets. I have a nice set of allen keys (~ 8" length) and have learned about how tight they need to be installed. I've never had a problem with them loosening, but I certainly wouldn't discourage the use of a torque wrench.

I would go with the torque wrench for the BB and other important fasteners.

The installation torque recommendation for almost all square taper cranks is in the 30 to 35 lb-ft range which is WAY more than you'd expect and more than nearly anyone can apply with a standard L-shaped allen wrench. Turbineblade is either very strong or has been lucky.

Torqued properly, a square taper crank should never loosen on it's own.

BTW. if your current crank has come loose and been retightened, it's a very good bet it has been damaged beyond use. Once the square socket in a crank arm has been distorted by being ridden loose, it will never fit properly again and must be replaced.

I turn the bike upside down, then lean on the end of the allen key handle while also leaning on the opposite crank arm for leverage. Over-tightening is a bigger thing to worry about actually.

I've used a torque wrench with a longer handle with the bike in a repair stand -- it's probably more accurate that way. Never done it with my own bikes, just shop bikes. No argument.

To install the bottom bracket, I use a breaker bar...well, not on the non-drive crappy plastic retainers, just tighten those pretty snug. I totally understand the potential for someone inexperienced to strip or trash parts this way. At the same time I personally think that there's *some value in learning how to tighten parts without a torque wrench, that's all.

Can of worms: dry or grease on axle? ;)

The objective of a torque setting is to attain a specified preload on the bolt. Actually measuring it is problematic. If the axle or threads are lubricated, getting to the preload setting is eaisier than with no lubrication. In other words, 30-35 lb-ft would over torque a lubricated asssembly than a dry one. Why? Friction, or the lack of it is part of the total equation. Torque settings typically are stated for dry assemblies unles otherwise stated or instructed. Some estimate that if the assembly is lubricated, reduce the torque value between 20 and 50%. Unfortunatly I have not a clue what the right adjustment is for any given assembly.

WRT using a torque wrench. Unless I am torqing the same bolt every day in the same application, I don't trust my judgement. Why take the risk, just to save a little time? Torque wrenches are very reasonably priced and proved peace of mind.

I generally loosen and re-tighten crank arm bolts a few times per season. I have an inch-lb torque wrench of my own but it only reaches 200, so I borrow the one from work that goes to 600in-lbs I think. Cheap insurance...

I have no problem with square taper myself. They will continue to be out there in good numbers on less expensive bikes. Treat them proper and they will last as long as any other.

That's an excellent way to destroy a square taper crank. Tighten it to the proper torque when you first install it and then leave it alone until you remove the arms for bottom bracket maintenance.

I don't know if Shimano bottom brackets are compatible with your cranks. I say this because people talking about FSA cranksets said it took FSA bottom brackets. In any case, I read the new BB-UN54 is not only better than the BB-UN26, I read Shimano combined the best qualities of the BB-UN74 and BB-UN26 to come out with the BB-UN54. So, this is the end of line for that series, but apparently the best one. Usually, square taper bottom brackets are compatible with all square taper cranks.

Having read all this, I'm glad I did not install my cranks yet. I thought about doing it on my own, now I'm having second thoughts. Hehe, might be a bit better to be safe than sorry. I might also have the headset installed by a shop as well.

There are two different square taper bottom bracket configurations, JIS and ISO. They are very similar and have identical 4° taper angles but ISO is slightly smaller at the start of the taper. So, theoretically an ISO crank won't go far enough up a JIS taper and a JIS crank will go too far up an ISO taper.

Shimano, Sun Tour, SR, most Suguino and most other Japanese cranks are JIS. Campy, other European and a few Suguino cranks are ISO.

As to FSA, if they are square taper they should fit a Shimano square taper bottom bracket. If they are ISIS, they are completely different.