O-ring

An O-ring is a ring of rubber or synthetic elastomer that sits in a groove and is squeezed between two parts to form a seal. Motorcycles use dozens of them: on oil filter covers, drain plugs, carburettor float bowls, fuel injectors, coolant pipes, fork caps and sensor bodies.

O-rings are also used in O-ring chains, where small rings between the side plates keep grease inside the chain rollers and dirt out.

Replace O-rings whenever you open a joint that uses one. Choose the right material (for example Viton for fuel and heat), lightly lubricate on fitting and make sure it is not twisted or nipped. Hard, flattened or cracked rings are the usual cause of small oil and fuel leaks.