Re: Evinrude 6202 6hp motor - 2 stroke or 4 stroke?
The difference between a two stoke and a four stroke:
A two stroke fires every revolution of the crankshaft (on every cylinder). It is called two stroke because that's one upward movement of the piston and one downward movement. The description
HEREis quite good. You will notice that the crankcase is involved in the admittance of the fuel/air mix and so cannot act as an oil reservoir. That is why the engine is lubricated by oil mixed in the fuel.
It's a bit difficult to understand that a 2 stroke actually works but of coure it does!
Click the link on the above webpage and you will get a rather brief explanation of a 4 stroke cycle. Called four stroke because it fires once very 2 revolutions of the crankshaft ie 4 strokes, two upward and two downward movements of the piston. The admittance of the fuel air mixture is controlled by a valve and the expulsion of the exhaust gases by another. On the first (downward) stroke the inlet valve opens and the fuel air mixture is drawn into the cylinder. The valve closes and the mixture is compressed by the next (upward) stroke. As the piston approaches the top of its stroke the mixture is ignited and the piston is driven down again by the force of the combustion. Finally as the piston rises again on the fourth stroke of the sequence the exhaust valve opens and the gases are expelled.
You will notice that the crank case in a four stroke engine is not involved in the transfer of the fuel air mixture so it can function as a reservoir (or sump) for lubricating oil. The oil is pumped to all the bearings etc by means of an internal pump.
Physically then the four stroke engine is distinguished by the oil sump the valves and a cam shaft and other components necessary to drive the cam shaft and operate the valves.
Both two and four stroke engines can have any number of cylinders and hence spark plugs from one upwards.