Yamaha - Oil Tank Cap Assembly Lubrication System Component 6H4-21770-01-00. Overview. I've learned not to overlook something as simple as an oil tank cap, especially on older two-stroke setups. A worn or loose cap can let air into the system or allow contamination, and that's where problems start. This updated version replaces the older one and gives you a better, more reliable seal. It's a small upgrade that helps keep your oil system doing its job without issues.. Key Features. Updated Replac