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S.No.
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Four-stroke engine
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Two-stroke engine
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1.
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It has one power stroke for every two revolutions of the crankshaft.
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It has one power stroke for each revolution of the crankshaft.
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2.
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A heavy flywheel is required and the engine runs unbalanced because turning moment on the crankshaft is not even due to one power stroke for every two revolutions of the crankshaft.
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The lighter flywheel is required and the engine runs balanced because the turning moment is more even due to one power stroke for each revolution of the crankshaft.
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3.
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Engine is heavy
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Engine is light
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4.
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Engine design is complicated due to the valve mechanism.
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Engine design is simple due to the absence of the valve mechanism.
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5.
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More cost.
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Less cost than 4 stroke.
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6.
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Less mechanical efficiency due to more friction in many parts.
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More mechanical efficiency due to less friction on a few parts.
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7.
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More output due to full fresh charge intake and full burnt gases exhaust.
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Less output due to the mixing of fresh charge with the hot burnt gases.
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8.
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Engine runs cooler.
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Engine runs hotter.
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9.
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These engines are water-cooled.
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These engines are air-cooled.
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10.
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Less fuel consumption and complete burning of fuel. Hence more thermal efficiency.
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More fuel consumption and the fresh charge is mixed with exhaust gases. Hence less thermal efficiency.
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11.
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The engine requires more space.
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The engine requires less space.
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12.
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Complicated lubricating system.
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Simple lubricating system.
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13.
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Less noise is created by the engine.
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More noise is created by the engine.
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14.
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The engine consists of an inlet and exhaust valve.
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The engine consists of inlet and exhaust ports.
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15.
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It consumes less lubricating oil.
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It consumes more lubricating oil.
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16.
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Less wear and tear of moving parts.
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More wear and tear of moving parts.
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17.
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Used in cars, buses, trucks etc.
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Used in mopeds, scooters, motorcycles etc.
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