31638-Zw5-004 Belt (4Pk720 M150) - Overview. The 31638-ZW5-004 Belt (4PK720 M150) is an essential component for Honda marine engine systems, supporting the alternator drive mechanism to keep your engine running smoothly. This belt plays a crucial role in transferring mechanical power to the alternator, ensuring consistent electrical output necessary for engine operation and battery charging. Manufactured to precise OEM specifications by Honda, it ensures seamless integration with existing parts,