2 Stroke Engines
Classic bike enthusiasts have started to collect 2 strokes in ever increasing numbers. With manufacturers phasing out their 2 stroke range due to emission problems, the availability of collectible machines has grown dramatically.
The working principles of a 2 stroke are the simplest of all internal combustion engines, with the least number of moving parts. The strengths of the 2 stroke design are its superior power-to-weight ratio (compared to a 4 stroke unit), and its ease of maintenance.
However, they do require more combustion chamber maintenance than a 4 stroke due to the oil burning characteristic.
Inlet and Compression
In a 2-stroke, some of the actions required to produce power happen simultaneously during the two vertical movements of the piston, hence the name, 2-stroke.
The starting point for all internal combustion engines can be considered the inlet phase. After the carburetor has mixed the fuel and air together, the mixture is drawn into the lower part of the engine. This is accomplished by the piston moving vertically.
As the piston moves up in the cylinder, the inlet port is uncovered and the area below the piston is depressurized creating the drawing effect.
Although this phase is classed as the inlet phase, the piston on its travel upwards is also compressing the previous mixture. Compressing the mixture in the cylinder head makes the mixed gases highly volatile; introducing a high voltage spark from the plug into this compressed mixture results in the power stroke as the piston is forced down again.
So how does a 2 stroke work? First it is necessary to become familiar with the major component parts:
Starting at the top, the cylinder head is dome shaped to create a space for the combustion of gases (gasoline and air mixed). Screwed into the cylinder head is a spark plug. Most 2 strokes utilize a single, centrally located plug.
However, many different designs have been tried, including twin plug heads.
The cylinder head is bolted to the cylinder (typically with 4 bolts). The cylinder contains various ports: inlet, exhaust and transfer (more about those later).
Supporting the cylinder and cylinder head are the crank cases-so called as they also carry the crankshaft. 2 stroke crankcases are split vertically on most designs; however the Japanese manufacturers preferred horizontal splitting cases on all of their engines with more than one cylinder. This horizontal splitting of the cases made assembly and disassembly much easier.
As the piston moves down, it accomplishes four things:
Central to the design of a 2 stroke engine are the transfer ports. The ports are a passage way between the crank cases and the upper part of the cylinder.
They are opened or closed with the vertical movement of the piston. The location of these ports is critical for the successful operation of the engine, and the manufacturers will have spent considerable time optimizing the location of them.
Classic bike enthusiasts have started to collect 2 strokes in ever increasing numbers. With manufacturers phasing out their 2 stroke range due to emission problems, the availability of collectible machines has grown dramatically.
The working principles of a 2 stroke are the simplest of all internal combustion engines, with the least number of moving parts. The strengths of the 2 stroke design are its superior power-to-weight ratio (compared to a 4 stroke unit), and its ease of maintenance.
However, they do require more combustion chamber maintenance than a 4 stroke due to the oil burning characteristic.
Inlet and Compression
In a 2-stroke, some of the actions required to produce power happen simultaneously during the two vertical movements of the piston, hence the name, 2-stroke.
The starting point for all internal combustion engines can be considered the inlet phase. After the carburetor has mixed the fuel and air together, the mixture is drawn into the lower part of the engine. This is accomplished by the piston moving vertically.
As the piston moves up in the cylinder, the inlet port is uncovered and the area below the piston is depressurized creating the drawing effect.
Although this phase is classed as the inlet phase, the piston on its travel upwards is also compressing the previous mixture. Compressing the mixture in the cylinder head makes the mixed gases highly volatile; introducing a high voltage spark from the plug into this compressed mixture results in the power stroke as the piston is forced down again.
So how does a 2 stroke work? First it is necessary to become familiar with the major component parts:
- Cylinder head (A)
- Cylinder (B)
- Ports (D = inlet, H = exhaust)
- Piston (C)
- Connecting rod (E)
- Crankshaft (F)
- Crank cases (G)
Starting at the top, the cylinder head is dome shaped to create a space for the combustion of gases (gasoline and air mixed). Screwed into the cylinder head is a spark plug. Most 2 strokes utilize a single, centrally located plug.
However, many different designs have been tried, including twin plug heads.
The cylinder head is bolted to the cylinder (typically with 4 bolts). The cylinder contains various ports: inlet, exhaust and transfer (more about those later).
Supporting the cylinder and cylinder head are the crank cases-so called as they also carry the crankshaft. 2 stroke crankcases are split vertically on most designs; however the Japanese manufacturers preferred horizontal splitting cases on all of their engines with more than one cylinder. This horizontal splitting of the cases made assembly and disassembly much easier.
As the piston moves down, it accomplishes four things:
- it transmits force/power to the crankshaft making it rotate
- it opens the exhaust port
- it compresses the new mixture in the crank case
- and finally, it uncovers the transfer port allowing the new mixture to enter the top part of the cylinder.
Central to the design of a 2 stroke engine are the transfer ports. The ports are a passage way between the crank cases and the upper part of the cylinder.
They are opened or closed with the vertical movement of the piston. The location of these ports is critical for the successful operation of the engine, and the manufacturers will have spent considerable time optimizing the location of them.
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