Small engines from many different manufactures are made as a 2 stroke or 4 stroke engine, but you may be wondering what the difference is between these two kinds of small engines.
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2-Stroke Engines
A two stroke engine is an engine that does not have valves, or a specified lubrication system. A two stroke engine is very simple, much simpler than the 4-stroke engine. It has very few working parts and is very light. This means that there is very little maintenance required and it is much cheaper to manufacture.
2-stroke engines are generally used in handheld lawn equipment because the power per weight is greater than 4-stroke engines; this means that a smaller engine will pack more power than a smaller 4-stroke engine. Engine life isn’t really a concern with a chainsaw like it would be with a vehicle, because they aren’t being used constantly so they will last long enough with the way they are generally used. They are also used in shorter time increments, so the problem of pollution is not as serious.
In a 2-stroke engine, it is required that oil be mixed in with the fuel, at a very precise ratio, in order to determine the ratio, you should check the owner’s manual of your equipment. The fuel and oil mixture running through the engine is what lubricates the parts, however, because it is not a specified lubrication system, these engines usually wear down quicker.
How it works:
This process can also be known by 2 kinds of strokes, the compression stroke and the power stroke. The compression stroke is when the piston moves upwards and compresses the fuel and air, or step 1/5. The power stroke is all of the other steps, the steps that actually produce the explosion and create the power.
Pros of a 2-Stroke Engine:
Cons of a 2-Stroke Engine:
4-Stroke Engines
A 4-Stroke engine is the kind of engine that is common on lawn mowers. It is heavy and has to remain in an upright position to be used, so it doesn’t work so well on lawn equipment such as weed eaters or chainsaws. They also are more expensive due to the complexity of the engine and the repairs that would be necessary to fix them if something went wrong.
A 4-stroke engine has a cycle that consists of 4 strokes, in those 4-strokes, the piston goes around twice in the engine, so the spark plug fires every other rotation. There are two separate valves in this kind of engine, one for intake and one for exhaust, unlike the 2-stroke engine.
In a 4-stroke engine, the oil is contained in the crankcase, and there is usually a splash lubrication system where the oil is released and the only job of the system is to keep everything lubricated. Because of this, the oil needs changed after a certain amount of hours and the level needs to be checked frequently. Since the only function is to keep everything moving smoothly, wear happens much slower on a 4-stroke engine than a 2-stroke engine.
How they work:
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1) The piston moves up and compresses a fuel and air mixture in the chamber (compression stroke)
2) Fuel is ignited by the spark plug and it drives the piston down providing the necessary momentum to keep the crankshaft turning (power stroke)
3) The piston moves back up and pushes the used/burned gasses out of the exhaust valve ( exhaust stroke)
4) The piston goes back down and draws the fresh air and fuel in preparation to move back up and compress the air (intake stroke)
Pros of a 4-stroke engine:
Cons of a 4-stroke engine:
Briggs and Stratton manufactures both 2-cycle & 4-cycle engines. Two-cycle engines are able to propel your lawn mower, snow blower or pressure washer in one crankshaft revolution and two strokes of the piston. The vast majority of the small engines Briggs & Stratton manufactures are 4-cycle engines, which require four strokes of the piston to complete a crankshaft revolution.
In this FAQ, you’ll learn:
How to Identify a 2-Cycle Small Engine
How To Determine the 2-Cycle Engine Oil Mix
The easiest way to determine if your small engine is a 2-cycle or 4-cycle is the number and type of fill ports (where you add either oil or gas) on the engine. Compare your gas cap and/or oil port with the images below.
The following 2-cycle stroke engine series was provided to outdoor power equipment manufacturers until about :
In addition, Briggs & Stratton has recently begun manufacturing the following model series for 2-cycle snow blower engines:
To determine if your engine model number is listed above, please check out The Your Small Engine Model Number page.
Since all 2-cycle small engines use the same fill port for both fuel and oil, a 2-cycle oil mix is necessary for your outdoor power equipment to function properly. The Specific oil/gas ratio for your lawn mower, snow blower or power washer can be obtained in your Operator’s Manual. Once you identify your oil/gas ratio, the following chart may be helpful, providing two common oil to gas ratios used in 2-cycle Briggs & Stratton engines.
50:1 Ratio
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