A healthy engine should not make metallic sounds from the outboard motor pistons. Piston slap occurs when an outboard motor piston rocks excessively within the cylinder. This usually means the outboard motor piston skirt has worn beyond spec.

Low compression on one cylinder suggests a problem with that outboard motor piston or rings. Removing the spark plug and peeking with a borescope can reveal outboard motor piston damage. Scoring or melting on the outboard motor piston indicates a lean fuel mixture.

A broken ring land on an outboard motor piston often results from detonation. When inspecting used outboard motor pistons, check for cracks around the wrist pin area. Excessive rocking will also damage the cylinder bore, not just the outboard motor piston.

Replacing only one outboard motor piston in a V6 is risky due to weight imbalance. If the outboard motor piston has a hole burned through, the injector was likely clogged. After a catastrophic failure, flush the crankcase to remove debris from the broken outboard motor piston.

Always lubricate the cylinder walls before inserting a new outboard motor piston. Following torque specs for the rod bolts prevents distortion of the outboard motor piston. By recognizing early signs of wear, you can replace outboard motor pistons before the engine seizes. Regular maintenance of outboard motor pistons ensures many seasons of reliable boating.