40100-ZW6-010 Engine (Lower) Case - Overview. The 40100-ZW6-010 Engine (Lower) Case is an essential component within Honda marine engine systems. It serves as the protective housing for critical lower unit engine parts, including gears, driveshaft, and water pump, ensuring these components remain secure and functional. This lower case plays a vital role in sustaining reliable engine performance and preventing water intrusion or mechanical damage, thereby maintaining smooth operation and longevit