1. + The Four Stroke Cycle By Elizabeth Fahey

2. + Outline Time Required: 1-3 classes Grades: 9-12 Background: Lesson is in conjunction with the small engine series. Students will have removed carburetor and fuel tank in previous labs. Related subjects: Math or Science

3. + Objectives Students will be able to identify engine components and their operations during the 4 stroke cycle. Students will demonstrate their understanding of the 4 strokes Students will describe the cause and effect created by the operations of the engine parts Students will analyze the piston and the valve movements and understand which stage the engine is in.

4. + Terminology Top Dead Center: In a reciprocating engine, the TDC is the when the piston is nearest to the crankshaft. Bottom Dead Center: In a reciprocating engine, the BDC is when the piston is furthest from the crankshaft. Piston: The piston is pushed through the cylinder by the force of expanding gases. Pushrod: A rod operated by cams that opens and closes the valves in an internal combustion engine. Intake Valve: An intake valve is in name for valve that allows air or fluid to pass through it, typically during the intake phase of an engine’s operation. Exhaust Valve: A valve through which burned gases from a cylinder escape into the exhaust manifold Crankshaft: a shaft having one or more cranks, esp the main shaft of an internal-combustion engine to which the connecting rods are attached Camshaft: a shaft having one or more cams attached to it, esp one used to operate the valves of an internal-combustion engine

5. + The 4 Stages Explained Intake Stage – the intake event occurs when the air-fuel mixture is introduced into the combustion chamber as the piston moves from TDC to BDC.

6. + Compression – the compression event is an operation event in which the trapped air fuel mixture is compressed to form the change.

7. + The ignition combustion event is an engine operation event in which the charge is ignited and rapidly oxidized through a chemical reaction to release heat energy. Combustion is the rapid, oxidizing chemical reaction in which a fuel chemically combines with oxygen in the atmosphere and releases energy in the form of heat. BTDC Before top dead center.

8. + Exhaust – As the piston reaches BDC during the power event, combustion is complete and the cylinder is filled with exhaust gases. The exhaust valve opens, and inertia of the flywheel and other moving parts push the piston back to TDC, forcing the exhaust gases past the open exhaust valve. At the end of the exhaust stroke, the piston is at TDC and one operating cycle has been completed. The volume that a piston displaces as it moves from TDC to BDC during the same piston stroke is called displacement.

9. + Activity Remove the head of the engine in order to examine the intake/exhaust valves and the pistons of the piston. Tools Needed: 3/8’’ drive, 7 mm socket, 8mm socket, 10 mm socket, ratchet wrench, extension, standard screwdriver, 5/8’’ spark plug socket, inch pound torque wrench, 5/8’’ box wrench, 1/8’’ Allen wrench, set of feeler gauges, pliers. 1. Using 7mm socket, remove the 4 screws securing outer end of Muffler Heat Shield to outer end of muffler. Using a 10 mm socket, remove bolts that secure inner end of the guard to the Governor Control Bracket. Remove Muffler Heat Shield.

10. + 2. Using 10 mm socket, remove the four screws, remove two bolts that secure the muffler in place. Remove muffler. Remove the gasket and check for damage. 3.Draw the valve cover bolt locations, noting the following: A. The top bolt next to the exhaust port is shorter than the other bolts. A longer bolt in this position may damage the muffler pipe. B. The bottom bolt has a different thread pitch as it is screwed into the head. *Put these bolts back into the same location when the engine is assembled. 4. Using a 10 mm socket, remove the four bolts that secure the valve cover to the head. Make note of bolt sizes, thread and position. Remove Valve Cover and check gasket for damage.

11. + 5. Loosen the Governor Control Bracket to remove the Cylinder Heat Shield. Do not remove the bracket at this time. Loosen the four bolts holding the bracket to the engine using a 10 mm socket. Turn the bolts about ¾ way out but do not remove them. 6.Move throttle to stop position, closing the the ignition ground switch and preventing spark at the spark plug wire. 7.Remove the spark plug using a 5/8’’ spark plug socket. 8.Using a 7mm socket, remove the bolt that secures the Cylinder Heat Shield to the engine. Lift up the Governor Control Bracket and work the shield out from the engine. 9.Pull the starter rope to move the piston through four strokes. Observe the overhead valve rocket arm movement. 10.Bring piston to just past dead center on the compression stroke. Use the flat feeler gauges to measure the air gap clearance between the rocker arm and the valve stem. The intake valve clearance should be.004’’ to.006’’ and the exhaust valve clearance should be between.009’’ to.011’’

12. + 11. Loosen the rocker arm nuts (5’8’’ wrench) and set screws ¼ turn, push down on the valve stem end of rocker arm and move arm away from the push rod. Remove push rod from head and mark each rod to identify as “intake” or “exhaust.” Remove valve cap from each valve stem and again mark each as “intake” or “exhaust.” 12. Using a 10mm socket remove the 4 head bolts that secure the head to the block. Remove the head. Remove the head gasket. *Pull on the starter rope and observe the movement of the piston. Take note of the position of the keyway on the PTO (Power Take Off) shaft when the piston is at TDC (Top Dead Center).