its not the arm thats bent its the bit that the chain runs on (crank?) thats all bent up so when riding the chain comes off,

iv had a look around and found some fairly cheap bb and cranksets,

iv measured the bb and it 113mm long, so am i right that its a 68x113 bb that i want?

im a student so looking for a quick fix for now and then upgrade later when i have more money, just need a bike to use at the moment to get to uni and back