he looked down at the gears and the chain and gearbox of the mountain bike. the gear chains are very dusty and greasy

back background bicycle bike black chain change close closeup cog cogwheel cogwheels component copy detail dirty disk drive dusty engineering force gear gearing gears gearshift gearwheel greasy hardware industry machine machinery mechanics mechanism metal mountain oil part power ratchet road service set shift space speed sport sprocket steel structure teeth tire transmission wheel worn