Bicycle Mechanics - when should bottom brackets be replaced?
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03-11-08, 05:34 AM
I have 14 spin bikes and recently a crank arm snapped, mid-arm. This caused me some alarm and I opted to change all crank arms on all bikes.
Now, just yesterday, a bottom bracket snapped...:mad:...should I replace all bottom brackets in all bikes or am I over reacting?
running out of spare parts...:(
A spin bike? Is that a stationary exercise bike?
Crank arms typically will last forever unless there is some specific problem. If one broke I would guess that either it had a defect from the outset or else was overtightened and weakened. Keep all those crank arms you took off, as they are probably still usable.
You "snapped a bb"? Not sure what this means. The BB refers to the axle thing that connects both crank arms (called a spindle) and the bearings and races that allow that spindle to spin smoothly. If someone broke a spindle, they must be a Gorilla. If the bearings crapped out, then that means that were poorly adjusted or greased. You should go around to the rest of them and spin them while not under load. They should have no perceptable wiggle but should feel smooth and not crunchy.
03-11-08, 10:51 AM
Do you change both tires when you get a flat? Wait - these bikes don't have tires, do they? Anyway, you get the point. If it's not broke, don't fix it.
03-11-08, 11:09 AM
So, you have 14 bikes, and they are in constant use.
You should check that the bottom brackets and crank arms are not loose. You should tension them accordingly.
03-11-08, 11:33 AM
.... If it's not broke, don't fix it.
My sentiments exactly.
Don't replace anything unless it breaks. If a recall was issued, you could find out about it from the CSPC.
It was probably a defect.
I didn't see anything about 'exercise bikes' being recalled.
If you think it should be recalled, report it to the CPSC using this link:
Am I correct in assuming that you own a gym or fitness center?
03-11-08, 11:36 AM
If someone broke a spindle, they must be a Gorilla.
Ever been to a spin class? The students aren't all aerobics instructors like in the videos...
Nothing bad about people wanting to work out, but many of them aren't cyclists and may be harder on the gear than someone with a developed spin. If you're already experiencing breakage, you may want to take the parts to an LBS and see what they would recommend would hold up better. For instance, if they come equipped with cheap cup and cone BBs, you may want to use a better grade of cartridge type.
03-11-08, 11:42 AM
I maintain a fleet of 20 StarTrac Spinner Pro bikes. I have had 1 crankarm snap. I only changed that 1 crank. First of all, the price to do so is too high, given the low failure rate. Secondly, the cranks get abused only when people do stupid or contraindicated moves on the bike (I am a STAR 3 Spinning instructor, BTW). The best way to eliminate this problem is to NEVER do lower body stretches on the bike or do sprints from a standing start. As for the bottom brackets, same advice applies. Replace the broken one, and leave it at that, unless you are getting play in the bearings. Another tip- make sure the class participants clean the bikes by spraying a rag or towel and using that to wipe the bike. These bikes have really cheap bottom brackets, and spraying disinfecting solution can dilute the bearing grease if it gets past the seals. ANy other questions, PM me. I'll answer what I can.
03-12-08, 06:37 AM
Yes, I am a fitness centre owner and the crank arm breaking on the Keiser Spin Bike resulted in some "law" related stuff even though it was a defect in the crank arm itself.
This incident turned out ok but I dont need the aggrevation again!
This is why I am concerned about this bottom bracket that has snapped ... faulty bottom bracket or should they be replaced overtime???
Bikes are used about 5 times a week and they are pretty experienced riders.
I am not one to fix something that isn't broken but I am not the only one using the equipment!!
03-12-08, 07:34 AM
You either had a defective bb or there is some user error going on. Make sure that your instructors are not doing calf stretches on the bike (dropping the heel with the bike stopped), or any other moves that places force on the cranks when they aren't moving. That is a sure way to overstress the cranks and bb spindle. They can take lots of force when they are moving, since they transfer most of the force through the drivetrain.
03-12-08, 08:17 AM
Don't replace anything unless it breaks.
Disassemble, inspect, and replace if necessary.
Waiting until parts fail is an accident waiting to happen.
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