SER FAQ: LMFAQ: The four strokes of a four stroke engine in living ASCII art

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NotTaR of small Gasoline Engines and Rotary Lawn Mowers : The four strokes of a four stroke engine..
Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.

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The four strokes of a four stroke engine in living ASCII art

You will just love the most excellent, accurate, and to-scale (:-).)ASCII renditions below but at least it will display on any computer using a fixed width font and not require half your disk space allocation for storage!

Note that the valves, normal operated by a camshaft driven off of a small gear on the crankshaft, are not drawn in their usual position for a common small (side valve) engine to improve the superb clarity of these drawings.

Intake stroke (1)

Air-fuel mixture is sucked into the cylinder by the by piston moving down driven by inertia of flywheel (and blade).

Intake valve: open.
Exhaust valve: closed.
Piston: moving down sucking in fresh air-fuel mixture from carburetor.


    From ignition/magneto coil >========
                                       || 
                                      ||||
                           Spark Plug ||||
                                      /||\  
            _________________________| || |________________________
           |  _______________________| || |______________________  |
           | |                          =="                      | |
           | |   ______   ->  ->  ->  ->  ->  ->  ->  ->  ->     | |
           | |__ \____/ ___   ->  ->  ->  ->  ->    ___ ______ __| |
           |____\  ||  /   | _____________________ |   \\____//____|
Air-fuel           ||  |   ||                     ||   |  ||
mixture from --->  ||  |   ||=====================||   |  ||
carburetor  ______ || /    ||=====================||    \ || ______ 
           |  ____||||___  ||=====================||  ___||||____  |
           | |     ||    | ||        |            || |    ||     | |
           | |     ||    | || Piston | O          || |    ||     | |
           | |           | ||        V  \         || |    ||     | |
           | |           | ||  _ _ _ _ _ \ _ _ _  || |           | |
           | |   Intake  | ||/           \       \|| |  Exhaust  | |
           | |   Valve   | |              \        | |  Valve    | |
           | |   Open    | |              \        | |  Closed   | |
           | |           | |          Rod  \       | |           | |
           | |           | |               \       | |           | |
                                            \
                                        ---> O  Crank pin journal
                                            /
                                          /
                                        /
                                       O  
                                 Main bearings

Compression stroke (2)

Air-fuel mixture is compressed as piston rises in sealed volume of combustion chamber driven by inertia of flywheel (and blade).

Intake valve: closed.
Exhaust valve: closed.
Piston: moving up compressing air-fuel mixture.


    From ignition/magneto coil >========
                                       || 
                                      ||||
                          Spark Plug  ||||
                                      /||\  
            _________________________| || |________________________
           |  _______________________| || |______________________  |
           | |                          =="                      | |
           | |               ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^               | |
           | |__ ______ ___  | | | | | | | | | | |  ___ ______ __| |
           |____\\____//   | _____________________ |   \\____//____|
                   ||  |   ||                     ||   |  ||
                   ||  |   ||=====================||   |  ||
            ______ || /    ||=====================||    \ || ______ 
           |  ____||||___  ||=====================||  ___||||____  |
           | |     ||    | ||            ^        || |    ||     | |
           | |     ||    | ||  Piston  O |        || |    ||     | |
           | |     ||    | ||         /  |        || |    ||     | |
           | |           | ||  _ _ _ / _ _ _ _ _  || |           | |
           | |   Intake  | ||/       /           \|| |  Exhaust  | |
           | |   Valve   | |        /              | |  Valve    | |
           | |   Closed  | |        /              | |  Closed   | |
           | |           | |       /  Rod          | |           | |
           | |           | |       /               | |           | |
                                  /
              Crank pin journal  O    
                                  \  
                                 ^  \ 
                                 |    \ 
                                       O
                                 Main bearings

Ignition

Compressed air-fuel mixture is ignited just before piston passes Top Dead Center (TDC) and starts down again.

Intake valve: closed.
Exhaust valve: closed.
Piston: just short of Top Dead Center moving up.


                                    ZAP!
    From ignition/magneto coil >========
                                       || 
                                      ||||
                          Spark Plug  ||||
                                      /||\  
            _________________________| || |________________________
           |  _______________________| || |______________________  |
           | |                          =="                      | |
           | |                       - X -                       | |
           | |__ ______ ___  _____________________  ___ ______ __| |
           |____\\____//   ||                     ||   \\____//____|
                   ||  |   ||=====================||   |  ||
                   ||  |   ||=====================||   |  ||
            ______ || /    ||=====================||    \ || ______ 
           |  ____||||___  ||                     ||  ___||||____  |
           | |     ||    | || Piston   O          || |    ||     | |
           | |     ||    | ||          |          || |    ||     | |
           | |     ||    | ||  _ _ _ _ | _ _ _ _  || |    ||     | |
           | |           | ||/         |         \|| |           | |
           | |   Intake  | |           |           | |  Exhaust  | |
           | |   Valve   | |      Rod  |           | |  Valve    | |
           | |   Closed  | |           |           | |  Closed   | |
           | |           | |           |           | |           | |
                                  ---> O
                                       | Crank pin journal
                                       |
                                       |
                                       |
                                       O
                                 Main bearings

Power stroke (3)

Heated expanding gases drive piston downward and apply power impulse to crankshaft via connecting rod (clockwise rotation).

Intake valve: closed.
Exhaust valve: closed.
Piston: moving down driven by combustion of air-fuel mixture.


    From ignition/magneto coil >========
                                       || 
                                      ||||
                          Spark Plug  ||||
                                      /||\  
            _________________________| || |________________________
           |  _______________________| || |______________________  |
           | |                          =="                      | |
           | |               | | | | | | | | | | |               | |
           | |__ ______ ___  V V V V V V V V V V V  ___ ______ __| |
           |____\\____//   | _____________________ |   \\____//____|
                   ||  |   ||                     ||   |  ||
                   ||  |   ||=====================||   |  ||
            ______ || /    ||=====================||    \ || ______ 
           |  ____||||___  ||=====================||  ___||||____  |
           | |     ||    | ||        |            || |    ||     | |
           | |     ||    | || Piston | O          || |    ||     | |
           | |     ||    | ||        V  \         || |    ||     | |
           | |           | ||  _ _ _ _ _ \ _ _ _  || |           | |
           | |   Intake  | ||/           \       \|| |  Exhaust  | |
           | |   Valve   | |              \        | |  Valve    | |
           | |   Closed  | |              \        | |  Closed   | |
           | |           | |          Rod  \       | |           | |
           | |           | |               \       | |           | |
                                            \
                                             O  Crank pin journal
                                            /
                                          /  |
                                        /    |
                                       O     V
                                 Main bearings

Exhaust stroke (4)

Exhaust gasses pushed out of cylinder by rising piston driven by inertia of flywheel (and blade).

Intake valve: closed.
Exhaust valve: open.
Piston: moving up pushing out exhaust gasses to muffler.


                           
    From ignition/magneto coil >========
                                       || 
                                      ||||
                          Spark Plug  ||||
                                      /||\  
            _________________________| || |________________________
           |  _______________________| || |______________________  |
           | |                          =="                      | |
           | |     ->  ->  ->  ->  ->  ->  ->  ->  ->   ______   | |
           | |__ ______ ___    ->  ->  ->  ->  ->   ___ \____/ __| |
           |____\\____//   | _____________________ |   \  ||  /____|
                   ||  |   ||                     ||   |  ||         Exhaust
                   ||  |   ||=====================||   |  ||    ---> gases to
            ______ || /    ||=====================||    \ || ______  muffler
           |  ____||||___  ||=====================||  ___||||____  |
           | |     ||    | ||            ^        || |    ||     | |
           | |     ||    | || Piston   O |        || |    ||     | |
           | |     ||    | ||         /  |        || |           | |
           | |           | ||  _ _ _ / _ _ _ _ _  || |           | |
           | |   Intake  | ||/       /           \|| |  Exhaust  | |
           | |   Valve   | |        /              | |  Valve    | |
           | |   Closed  | |        /              | |  Open     | |
           | |           | |       /  Rod          | |           | |
           | |           | |       /               | |           | |
                                  /
              Crank pin journal  O --->
                                  \  
                                    \ 
                                      \ 
                                       O  Main bearings

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