The lower unit and drive system of an outboard motor has a lot of parts—from o-rings to seals to flywheels to dozens of others. But one little part is the unsung hero of the outboard motor, and that’s the boat engine gasket. Gaskets are often overlooked, but they’re particularly important on boat motors. Because outboard motors work using a precise mixture of fuel and air, other materials—like water, for example—can cause things to break down and not work as efficiently. This is of obvious concern given that an outboard is meant to drive a boat through water. Gaskets help keep water outside of the engine, where it belongs. The head gasket sits in between the cylinder block (where the spark plugs live) and the cylinder head. It seals these parts together, which helps them withstand the intense compression they undergo. It also allows water to flow between the block and the head without entering the engine. However, because of the heat and—if you’re boating in the ocean—saltwater they’re often exposed to, head gaskets often corrode and break down over time. If they’re not replaced, water then enters the engine and causes numerous issues and lead to serious engine damage. Use our Marine Engine Parts Selector Tool to find the right engine parts for your boat.