Yamaha - Oil Tank Cap Assembly Lubrication System Component 6H4-21770-00-00. Overview. It's easy to overlook something like an oil tank cap until it starts causing problems. I've seen loose or worn caps let air or moisture into the system, and that's not something you want anywhere near your oil supply. This piece helps keep everything sealed and working the way it should. When it's doing its job, you don't think about it-but when it's not, it can lead to bigger issues.. Key Features. Secure Tank Seal - Helps maintain a tight seal to protect the oil supply from contamination.. Proper Venting Function - Supports correct airflow to allow consistent oil delivery.. OEM Fitment Design - Built to Yamaha specifications for reliable fit and sealing.. Durable Cap Construction - Designed to handle heat, vibration, and marine exposure.. Supports System Integrity - Helps ensure the oil injection system operates without interruption.. Engine & Boat Compatibility. Designed for Yamaha outboards equip