Pedals Keep LooseningUpdated 6 months ago

It is very likely that you have stripped your crank arm if the pedals no longer stay in the cranks.

Unfortunately, manufacturer warranties are to cover defects in materials or workmanship that occur within the normal lifespan and use of the product. In this case, the manufacturer would deem this an improper assembly and wouldn't cover it under their warranty policy. 

Left side crank arms are reversely threaded. This ensures safety while riding; if bearings seize up, the pedal will not unthread itself as you turn the cranks. This is a prevalent cause of stripped threads if the assembler is not aware. 

Right and Left crankarms can also become stripped from not being installed securely and then experiencing blunt force. If the bike is dropped or falls, the pedal is the first thing to hit the ground and if not properly torqued the threads can become damaged.