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2-4 Stroke Engine Differences, Applications

and Lubrication Needs

2-stroke and 4-stroke engines operate under different conditions, requiring different lubrication methods.

2-stroke and 4-stroke engines operate under different conditions, requiring different lubrication methods.Internal combustion engines are used to produce mechanical power from the chemical energy contained in hydrocarbon fuels. The power-producing part of the engine’s operating cycle starts inside the engine’s cylinders with a compression process. Following compression, the burning of the fuel-air mixture releases the fuel’s chemical energy and produces high-temperature, high-pressure combustion products. These gases expand within each cylinder and transfer work to the piston, producing mechanical power to operate the engine.

Each upward or downward movement of the piston is called a stroke, and the two commonly used internal combustion engine cycles are the two-stroke cycle and the four-stroke cycle. The terms "two-cycle" and "two-stroke," as well as "four-cycle" and "four-stroke," are often interchanged.

Two-Stroke and Four-Stroke Differences

The fundamental difference between two-stroke and four-stroke engines is in their gas-exchange process, or more simply, the removal of the burned gases at the end of each expansion process and the introduction of a fresh mixture for the next cycle. A two-stroke engine has an expansion, or power stroke, in each cylinder during each revolution of the crankshaft. The exhaust and the charging processes occur simultaneously as the piston moves through its lowest or bottom center position. In a four-stroke engine, the burned gases are first displaced by the piston during an upward stroke, and a fresh charge enters the cylinder during the following downward stroke.

Four-stroke engines require two complete turns of the crankshaft to make a power stroke, compared to the single turn necessary in a two-stroke engine. Two-stroke engines operate on 360° of crankshaft rotation, whereas four-stroke engines operate on 720° of crankshaft rotation.

Applications

Two-stroke engines are generally less expensive to build compared to four-stroke engines, and they are lighter and can produce a higher power-to-weight ratio. For these reasons, two-stroke engines are ideal in applications such as chainsaws, weed trimmers, outboard motors, off-road motorcycles and racing applications. Two-stroke engines are also easier to start in cold temperatures, making them ideal for use in snowmobiles. Four-stroke engines, on the other hand, produce more torque at lower rpm, generally providing greater equipment durability than high-revving two-stroke engines, while also providing greater fuel efficiency and lower emissions. For these reasons, four-stroke engines are ideal in applications such as motorcycles, ATVs and personal watercraft.

Four-Stroke Lubrication

Four-stroke engines are lubricated by oil held in an oil sump. The oil is distributed through the engine by splash lubrication or a pressurized lubrication pump system; these systems may be used alone or together.

Splash lubrication is achieved by partly submerging the crankshaft in the oil sump. The momentum of the rotating crankshaft splashes oil to other engine components such as the cam lobes, wrist pins and cylinder walls.

Pressurized lubrication uses an oil pump to provide a pressurized film of lubricant between moving parts such as the main bearings, rod bearings and cam bearings. It also pumps oil to the engine’s valve guides and rocker arms.

Two-Stroke Lubrication

Two-stroke engines collect some oil beneath the crankshaft; however, two-stroke engines employ a total-loss lubrication system that combines oil and fuel to provide both energy and engine lubrication. The oil and fuel are combined in the cylinder’s intake tract and lubricate critical components such as the crankshaft, connecting rods and cylinder walls.

Oil-injected two-stroke engines inject the oil directly into the engine, where it mixes with the fuel, while pre-mix two-stroke engines require a fuel-oil mixture that is combined before being installed in the fuel tank. In general, two-stroke engines are known to wear more quickly than four-stroke engines because they don’t have a dedicated lubricant source; however, high-quality two-stroke oil significantly reduces engine wear.

AMSOIL provides a full line of premium synthetic two- and four-stroke oils that provide outstanding protection and performance for recreational and work equipment.

AMSOIL SYNTHETIC 2-STROKE OIL

Injector Oil

AMSOIL Synthetic 2-Stroke Injector Oil offers the convenience of one formula for the tough conditions of all two-stroke recreational equipment. It is tested and proven to minimize wear and deposits that can damage internal components. Provides quality and affordability for cost-conscious enthusiasts who want the benefits of synthetic two-stroke oil.

HP Marine Oil

Excellent for Evinrude® E-TEC™ factory-lean setting (replaces Evinrude XD100™ 2-Cycle Oil). Helps prevent deposits, protects against wear, has low smoke, protects against rust and has low aquatic toxicity. Superior performance as an injection oil or at 50:1 pre-mix.

INTERCEPTOR®

High-performance 2-stroke oil with an emphasis on exhaust power valves. Contains high levels of detergent additives to prevent valve sticking. Replaces manufacturer-branded oils. Injector use or 50:1 premix. Excellent in snowmobiles, motorcycles, PWC, ATVs and jet boats.

DOMINATOR®

This complex blend of oils and additives directly addresses the heat, pressure and friction of race-engineered engines. These engines operate on the edge, yet engine reliability is critical. DOMINATOR does an outstanding job protecting high-performance engines.

VIEW 2 STROKE OILS

SABER® Professional

Designed for pre-mix applications as lean as 100:1 ratios or richer. Improves throttle response and lowers or eliminates smoke. Minimizes deposit formation and lowers emissions. Performance emphasis on hand-held power equipment such as chainsaws and lawn/utility equipment.

Outboard 100:1 Pre-Mix

Designed for pre-mix applications as lean as 100:1 ratios or richer. Improves throttle response and lowers or eliminates smoke. Minimizes deposit formation and lowers emissions. Performance emphasis on hand-held power equipment such as chainsaws and lawn/utility equipment.

Synthetic Chaincase & Gear Oil

Provides superior protectionand performance for enclosed chains and gears found in snowmobiles, ATVs and general equipment. Formulated with extreme-pressure additives, it helps extend chain and gear life through increased wear protection. Repels water, while also inhibiting rust, oxidation and foam. Its low pour point ensures superior low-temperature starting, reducing drag to deliver maximum power.

Semi-Synthetic Bar and Chain Oil

Tacky formula clings to metal surfaces better than other oils. Delivers unparalleled lubrication and protection. Anti-wear additives extend the life of bar and chain applications. Ideal for chainsaws.

AMSOIL Synthetic 2-Stroke Oil Saves Racing Engine

After a successful weekend of racing during the opening rounds of AMSOIL Championship Snocross over Thanksgiving weekend, AMSOIL/Scheuring Speed Sports driver Lincoln Lemieux made the Pro Open final on Sunday.

“We’ve worked with AMSOIL the last 20 years developing two-stroke oils for our race sleds. In my opinion, I believe 100 percent the reason that motor lived was because of the AMSOIL products.”

Lincoln Lemieux

AMSOIL SYNTHETIC 4-STROKE OIL

10W-30 Synthetic Small Engine Oil

Formulated to outperform passenger-car/light-truck oils, AMSOIL Synthetic Small-Engine Oil protects against wear, deposits and oil consumption in over-worked, under-maintained small engines professionals rely on to make a living.

10W-40 Synthetic Small Engine Oil

AMSOIL Synthetic Small-Engine Oil is a tough formulation designed to preserve engine power while fighting oil consumption, helping professionals work more efficiently and save money on maintenance.

Formula 4-Stroke Power Sports Synthetic Motor Oil

Specially formulated for 4-stroke recreational motors, ATVs and snowmobiles. Reduces wear. Wet-clutch compatible. Contains no friction modifiers. Broad viscosity range makes it excellent for use in both hot and cold weather conditions.

Formula 4-Stroke Synthetic Scooter Oil

Meets the needs of today's high-tech air- and water-cooled four-stroke motorized scooters. Unsurpassed wear protection and friction reduction for longer equipment life. Protects transmissions and gear boxes. Wet-clutch compatible to insure smooth clutch operation. Provides long-term protection during storage.

VIEW 4 STROKE OILS

10W-40 Synthetic Dirt Bike Oil

Engineered to deliver the performance attributes most requested by on- and off-track dirt bike riders, including consistent clutch feel. AMSOIL-exclusive advanced chemistry provides outstanding engine reliability for worry-free operation under severe conditions.

10W-50 Synthetic Dirt Bike Oil

Engineered to deliver the performance attributes most requested by on- and off-track dirt bike riders, including consistent clutch feel. AMSOIL-exclusive advanced chemistry provides outstanding engine reliability for worry-free operation under severe conditions.

10W-60 Synthetic Dirt Bike Oil

Engineered to deliver the performance attributes most requested by on- and off-track dirt bike riders, including consistent clutch feel. AMSOIL-exclusive advanced chemistry provides outstanding engine reliability for worry-free operation under severe conditions.

Briggs & Stratton Synthetic 4T Racing Oil

Synthetic 4T Racing Oil is proven in the lab and on the track to provide increased performance in kart, junior drag, quarter midget and other racing applications. It offers benefits other oils simply can’t match.