**Always follow the instructions in your repair manual when doing repair or maintenance work on Outdoor Power Equipment. Manuals can be found at the manufacturers website.**
The 4 stokes of a 4 stroke or cycle engine are:
1) Intake: During the intake stroke the piston moves from the very top of its stroke (TDC-Top Dead Center) to the very bottom of its stroke (BDC-Bottom Dead Center), and the intake valve opens at the start of this stroke letting in a fresh air and fuel mixture, and closes near the bottom of this stroke.
2) Compression: During the compression stroke the piston moves from BDC to TDC compressing the fresh air and fuel mixture.
3) Power: The air and fuel mixture is ignited at the start of the power stroke. The heat from the air and fuel burning forces the piston to move from TDC to the BDC.
4) Exhaust: During the exhaust stroke the piston moves from BDC to TDC, and the exhaust valve opens at the start of this stroke to let out the burnt air and fuel mixture from the power stroke, and closes at the end of this stroke.
After the 4 strokes or cycles the process repeats in this order. If you know the 4 cycles of a 4 stroke engine you can determine what stroke the piston is in and roughly know where the piston is by viewing the intake and exhaust valves.
Thank you for Watching!