This video shows what happens inside a four-stroke engine. That’s:
1. the intake stroke of the piston, reducing pressure in the cylinder and forcing gas and air inside
2. intake and exhaust valves close and the piston compresses the fuel-air mix
3. the compression and a spark result in combustion, and therefore a power stroke
4. the piston compresses, pushing out the expended fuel-air mix
By way of Neatorama