Marine Engine Parts Glossary: 40 Terms Buyers Need to Know

Most sourcing mistakes start with a word rather than a number. Someone asks for a liner when they mean a liner kit, or a bearing when they mean a shell, and two weeks later the wrong box is in the container. This is the vocabulary we use, in plain terms, with the confusion flagged.

The expensive version of this mistake involves a crane and a surveyor.

Cylinder unit

• Cylinder liner — the removable bore that the piston runs in; replaced on wear measurement.
• Piston crown — the top of the piston, exposed to combustion; often a separate component on two-stroke engines.
• Piston skirt — the lower body of the piston that guides it in the liner.
• Piston ring — compression and oil control rings seated in the crown grooves.
• Cylinder cover — the head of a two-stroke cylinder, carrying the exhaust valve and injector.
• Exhaust valve — the large valve that releases combustion gas on a two-stroke engine.
• Valve seat / valve cage — the replaceable seat that the valve closes against.

Fuel injection

• Fuel injector — atomises fuel into the combustion chamber.
• Nozzle — the tip of the injector; a wear item replaced on running hours.
• Plunger and barrel — the pumping element of a fuel injection pump.
• Delivery valve — controls fuel flow from pump to injector.
• Fuel pump — the high-pressure pump that meters fuel per stroke.

Air and exhaust

• Turbocharger — driven by exhaust gas, it pressurises intake air.
• Nozzle ring — the ring of guide vanes that directs gas onto the turbine.
• Diffuser — converts compressor velocity into pressure.
• Charge air cooler — cools compressed air before it enters the cylinder.
• Air filter element — removes dust and salt from intake air; see the air filter guide.
• Scavenge air — air used to clear exhaust gas from a two-stroke cylinder.

Cooling and lubrication

• Heat exchanger — transfers heat between two fluids without mixing them.
• Cooler stack / tube bundle — the removable core inside a shell-and-tube cooler.
• Thermostatic valve — regulates cooling water temperature.
• Lube oil pump — circulates oil to bearings and cylinder feeds.
• Lube oil cooler — removes heat from circulating oil.
• Duplex filter — two-element filter that can be switched without stopping flow.

Bearings and running gear

• Main bearing — supports the crankshaft in the bedplate.
• Connecting rod bearing — the big-end bearing between rod and crankpin.
• Thrust bearing — takes the axial load from the propeller.
• Crosshead bearing — two-stroke only; carries the combustion load from piston rod to connecting rod.
• Housing and bush — the outer carrier and inner bearing surface.

Sealing and fastening

• O-ring — elastomer seal used throughout the engine.
• Gasket — a shaped seal between two flat faces.
• Stuffing box — seals the piston rod where it passes through the diaphragm.
• Mechanical seal — used on pumps; face-type rather than compression.
• Stud and nut — the fastening combination used on high-load joints.

Commercial and documentation

• OEM genuine — made by or for the engine designer.
• OEM-equivalent — made to the same drawing by another manufacturer.
• Mill certificate — material certification traceable to the heat number.
• Class certificate — issued or endorsed by a classification society.
• Supersession — the replacement of an old part number by a new one.
• Lead time — time from order to dispatch, not to delivery.
• RFQ — request for quotation; see the RFQ checklist.
• Incoterms — delivery terms such as EXW, FOB, CIF and DAP.

Reading the system pages puts these terms in context: marine engine parts lists all ten groups.