My bicycle's crank is sorta wobbly - it tilts left or right, according to pressure applied to pedals.
How do I fix it? What tools do I need?
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The "bottom bracket" assembly is loose. It may just be that it's a one-piece "cartridge" and is rattling around in the frame, or it may be that the unit is "loose bearings" and the bearing caps need to be adjusted. Or there may have been some sort of failure of the bearings.
Regardless, the whole mess will need to be disassembled to a degree, and that requires some special tools (mainly a "crank puller"). So it may be best to take it to a bike shop.
Ran into virtually the identical situation today, working on a donated bike. To do the job properly you need a crank puller, a "spanner" for the lockring, and a Park HCW-11 wrench for the "slotted" bottom bracket cup. There are ways to do it without those special tools, but you risk mucking up the threads, etc. And you probably need a new set of bearings (they're likely in "cages").
Looks to me like it is an american to square taper conversion BB, they look like this out of the frame if that is indeed what it is.
If that is correct it may just need tightening, also if the BB shell hasn't been damaged you can just get replacement bearings from you LBS if just the bearings are bad. Either option is relatively inexpensive. Tool wise if it is this style of BB you should be able to dissemble it with basic home tools for the most part, spanner wrench, allen wrenches, etc but it will more than likely require a crank puller to remove the arms from the axle. YouTube will be your best friend for this sort of repair, its pretty basic but any bottom bracket work can turn into a pain if you haven't done it before.
You can google American to square taper bottom bracket installation and i'm sure you will find a plethora of information regarding the repair. Although your best option would probably be to take it to a shop. Should be a reasonably easy repair for them unless anything else has been damaged by the loose part.
Anyone that knows more feel free to correct me if I'm wrong, but that's what it appears to be to me at first glance.
In case this is of any use to anyone, I've a BTwin Rockrider 500 which had the same symptoms (right pedal tilted downwards approx 2mm and left pedal tilted upwards approx 2mm simultaneously and vice versa when bike being pedalled).
It was almost imperceptible when new but steadily got more and more noticeable until it was really doing my head in.
After much research on t'internet...
I bought a cheap Silverline 241459 bottom bracket tool with 20 splines and a 32mm socket, took the left pedal allen bolt out with an allen key (anti-clockwise), removed the pedal with a bit of leverage near the crank from a big screwdriver, tapped the bottom bracket tool into the splines (it was quite a tight fit) and tightened the bottom bracket (clockwise) until it was tight but not very tight (I don't have a torque wrench).
This 100% fixed the problem and cost me approx £7 in total.