4-Stroke

2-Stroke

In four stroke engine all the four operations i.e. suction, compression, ignition and exhaust are completed in two revolutions of crank shaft.

In two strokes engine all the four operations are completed in one revolution of the crank shaft.

Power is developed in every alternate revolution of the crankshaft.

Power is developed in every revolution of the crankshaft.

The torque is less uniform; hence a four stroke engine requires a heavier flywheel.

The torque is more uniform than in the four stroke engine hence a lighter flywheel is necessary in a two stroke engine.

The suction and the exhaust are opened and closed by mechanical valves in a four stroke engine

In a two stroke engine, the piston itself opens and closes the ports

In a four stroke engine the charge directly enters into the cylinder

in a two stroke engine

the charge first enters the crankcase and then flows into the cylinder

The crankcase of a four stroke engine even though closed is not a pressure tight chamber.

The crankcase of a two stroke engine is a closed pressure tight chamber

In a four stroke engine the piston drives out the burnt gases during the exhaust stroke.

whereas, in a two stroke engine the high pressure fresh charge scavenges out the burnt gases

The lubricating oil consumption in a four stroke engine is less.

The lubricating oil consumption in a two stroke engine is more than in four stroke engine.

A four stroke engine produces less noise.

A two stroke engine produces more noise than a four stroke engine.

Since the fuel burns in every alternate revolution of the crankshaft in a two stroke engine the rate of cooling is more than in a four stroke engine.

Since the fuel burns in every revolution of the crankshaft in a two stroke engine the rate of cooling is more than in a four stroke engine.

A four stroke engine cannot run in either direction.

A valve less two stroke engines runs in either direction