Yamaha Oil Tank Cap Assembly - 6H4-21770-00-00Yamaha Oil Tank Cap Assembly Lubrication System Component 6H4 21770 00 00 Overview Its easy to overlook something like an oil tank cap until it starts causing problems. Ive seen loose or worn caps let air or moisture into the system, and thats not something you want anywhere near your oil supply. This piece helps keep everything sealed and working the way it should. When its doing its job, you dont think about itbut when its not, it can lead to bigger