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Pistons - Marine Parts House
Pistons - Marine Parts House
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Pistons, DESCRIPTION, Boat Parts, Boat Motor Parts, Volvo Penta Parts, Omc Parts, Mercruiser Parts, Johnson Evinrude Parts

Need help finding the right part for your boat motor? Send us an email by clicking here or use our "Advanced Search" tool to search for an OEM number, GLM number, or Sierra number.

GLM Exclusive Marine Pistons / Piston Ring Coatings Comparision  -->
Piston Designs (Crossflow, Loopcharged & Four-Stroke)  -->
Inline 4-Cynlinder Crossflow Pistons  -->
2 & 3-Cylinder Loopcharged Pistons  -->
Inline 2, 3, 4 & 6 Cylinder Crossflow Pistons  -->
3-Cylinder Loopcharged Pistons  -->
Inline 3 & 4 Cylinder Loopcharged Pistons  -->
60 V6 Loopcharged Pistons  -->


There are three basic piston designs used in Mercury / Mariner / Force engines:
Crossflow, Loopcharged and Four-Stroke.


The oldest design, and the one used on Mercury / Mariner /Force 35-150 HP engines from 1970- 1990 is the crossflow piston. As the air / fuel mixture travels through the transfer port and into the cylinder, a deflector, cast into the top of the piston, directs the air / fuel mixture towards the combustion chamber and spark plug tip for maximum efficiency. All engines with deflectors on top of the pistons will be crossflow engines. External inspection of a crossflow engine will reveal removeable transfer port covers on the side of the cylinders.

In 1976 Mercury / Mariner /Force introduced a V6 engine with loopcharged pistons. This engine was the V-175 HP 6-Cylinder. A loopcharged engine has a transfer port cast into the cylinder wall in such a way that it will direct the air / fuel mixture towards the combustion chamber and spark plug tip without the need for a piston deflector. All engines with a flat top or a slight dome on the top of the pistons will be loopcharged. Loopcharged engines will not have removable transfer port covers on the side of the cylinders.

Four-stroke / four-cycle engines are fairly new to the marine industry. They have become the engine design preferred by most marine engine manufacturers to meet government mandated exhaust emission standards. Oil stored in the crankcase of these engines is splashed onto the cylinder walls for piston and ring lubrication.The pistons are equipped with oil control rings to scrap excess oil off of the cylinder walls. Four-stroke / fourcycle pistons are easily identified by a three piece oil control ring in the bottom ring position. The pistons almost always have a flat top or a dished top and never have needle bearings between the wrist pin and connecting rod (like two-stroke engines).

Not sure which part you need? Find the part number in the chart below and search for that part number using our "Product Search" tool found in the upper left hand corner of this page.

For instance, if you have a 30(2-Cly.)(644cc), made in the USA you would search for "STD Piston" number 14790.

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