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Most people know two- and four stroke engines have different lubrication requirements, but many don't know why. The differences in lubrication requirements are a direct result of the differences in the two- and four- stroke combustion processes

Four-stroke engines common in automotive applications are continuously lubricated by a single source of filtered oil. Two-stroke engines, however, are lubricated by oil that is consumed during the combustion process. In addition, combustion occurs on every revolution of the crankshaft in a two-stroke application, compared to every-other revolution in a four-stroke engine, which generates more heat and places greater demand on the lubricant. The oil burned in the two-stroke combustion process can leave deposits on the piston crown, skirts and ring grooves. Two-stroke oil must be formulated to burn as cleanly as possible and control deposit formulation; excessive deposits can result in engine failure. The high heat and tendency for deposit formulation in two-stoke engines necessitate an oil with excellent lubricity, detergency and ability to prevent pre-ignition.

Lubricity describes an oil's friction-reduction properties. Lubricity is critical for managing the excess heat and high operating rpm common in two-stroke engines. High heat is generated not only from the rapid combustion process, but also from piston-to-cylinder friction. Two-stroke applications require a lubricant that withstands the heat. If the oil burns off too easily from combustion or does not provide the needed lubricity for piston lubrication, piston scuffing will occur, causing lost performance and even engine failure.

Detergency describes a lubricant's ability to control engine deposits. In two-stroke engines, deposit control is especially important on the piston skirt and ring areas in order to prevent ring jacking and ring sticking. Ring jacking occurs when deposits accumulate behind the piston rings and force them against the cylinder wall, rupturing the lubricant ring. Ring sticking is caused by deposit formulation on the top and bottom of the ring within the ring groove that prevents the ring from forming a proper seal seal in the cylinder. If a proper seal is not formed, gases and heat from the combustion process can escape past the piston and burn the protective the protective lubricant off the cylinder wall. This is known as blow-by which, again, results in piston scuffing, lost performance and even engine failure. A quality two-stroke oil must contain enough detergency to prevent engine failure from ring jacking and ring sticking.

Prevention of pre-ignition in the combustion chamber is important for efficient two-stroke operation. If the by-products of burned fuel and oil accumulate inside the combustion chamber, deposits can build on top of the piston (the crown). Piston crown deposits can absorb heat from the burning fuel and oil, creating hot spots that can ignite the fuel/oil mixture before the spark plug fires, which is known as pre-ignition. Pre-ignition can cause the temperatures and pressures in the combustion chamber to rise beyond the failure limits of the piston and head gasket, resulting in catastrophic engine damage. Ultimately, prevention of pre-ignition requires a lubricant carefully formulated with the proper detergent additives in the right amounts for effective deposit control.

The three areas identified- lubricity, detergency and prevention of pre-ignition- are critical to engine operation. There are other areas of importance too, including exhaust port deposit control to keep exhaust valves functioning, fluidity for oil injection systems, miscibility for mixing oil with gasoline at cold temperatures and rust protection for storage. Specifications are in place to help consumers choose the right oil for their applications. Two-stroke specifications are developed and managed by multiple governing bodies, including the Japanese Automobile Standards Organization (JASO), the International Standards Organization (ISO) and the National Marine Manufacturers Association (NMMA). The American Petroleum Institute (API) also has a specification for two-stroke engine oils. Most of these organizations have adopted standards focused on lubricity, detergency and prevention of pre-ignition.

Of the current two-stoke specifications, NMMA TC-W3 is probably the most well-known. It was developed by marine engine manufacturers for water-cooled outboard engines; however, it has been deemed appropriate for other two-stroke engines by many manufacturers of land-based two-stroke engines. API TC is a long-standing specification that applies to air-cooled engines, which may include those with a radiator. JASO and ISO two-stoke specifications apply to air-cooled engines commonly found on handheld power equipment.

AMSOIL products are tested to ensure they not only meet, but surpass the demands of the engine and operating environment for which they are developed. We recognize the importance of performance and reliability, which is why we engineer our two-stroke oils with high-quality chemistries to exceed industry standards and address specific demands of various two-stroke applications. In general, AMSOIL DOMINATOR® is ideal for two-stroke racing applications; AMSOIL INTERCEPTOR® is ideal for two-stroke recreational equipment; HP Injector® and Saber® Outboard are ideal for two-stroke marine equipment; Saber® Professional is ideal for handheld power equipment. For specific product recommendations and specifications, Click Here.