A connecting rod links the crankshaft to the piston.
Pistons can change direction hundreds of times a second and are exposed to extremes of heat and pressure. Modern pistons are made of aluminum alloy.
The crown of the piston can be flat, concave, domed or recessed. Or, as in some 2-strokes it may have a deflector.
When the piston is fitted to the cylinder, there must not be too much clearance. It has to seal in huge pressures and temperatures generated by combustion. This is done by piston rings held in grooves in the side of the piston.
The top two are called compression rings.
The lower ring is an oil control ring. It scrapes excess oil off the lower cylinder walls.
Since 2-stroke petrol engines are usually lubricated by oil mixed with the petrol, they don’t need this oil control ring.
