1. The piston operates in an up and down, or back and forth motion within a cylinder.

2. The piston is connected to a crankshaft that converts the up and down motion to a rotary motion, which powers the implement.
crankshaft:

3. The crankshaft extends through the crankcase and is attached to a flywheel at one end and a blade, gear, transmission or pulley at the other end.
Crankcase

4. The cylinder is capped with a thick plate called a Head, which seals the cylinder.
Cylinder Head
Head Bolts

5. Engine Block & Valves
Within the block are two valves: Intake and Exhaust
valves
piston

6. The valves operate by means of a Camshaft
The valves operate by means of a Camshaft. Which is powered by a gear on the crankshaft
As the camshaft turns, the lobes push open the valves with precise timing so that intake and exhaust occur at the right instant.
Lobes
Camshaft
Camgear

7. In the engine, the mixture is ignited, and the burning gases provide the force to drive the piston.
Ignition in the combustion chamber occurs in the form of an electrical spark from the spark plug.

8. The spark at the spark plug comes from a process known as electrical induction.
This begins with the flywheel.
Flywheel
magnet

9. In a four-stroke engine, moving parts are lubricated by motor oil.
In most small engines, the oil is located in the bottom of the crankcase in the oil sump, and is distributed throughout the engine to vital parts by means of a oil slinger or oil dipper depending upon the crankshaft position.
oil sump

10. Two Cycle Engines

11. Two- cycle engines are typically used in smaller, hand-held equipment like chainsaws and string trimmers because they can be smaller and lighter than four-cycles.
Also:
Used in these types of equipment because unlike four-cycle engines, two cycle engines can operate on their side or even up-side down

12. The two cycle engine completes its cycle of intake, compression, power, and exhaust with only two strokes of the piston.
It takes only one revolution of the shaft to complete the 2-stroke cycle.

16. Two cycle engines do not have an oil sump.
Critical parts of the engine are lubricated by oil that is mixed with the fuel.

17. Small Engine Parts Four-Cycle
By Katie Murray, UGA Agriculture Education
Edited by Georgia Agriculture Education Curriculum Office
May 2006
1. Crankcase
Revised May 2007

18. Engine Block
2. Cylinder Block
1. Crankcase
Crankcase Cover

19. Cylinder Block 1. Cylinder Bore 3. Cooling Fins 2. Valves
Head gasket goes here
3. Cooling Fins
2. Valves

20. Spark Plug
Cooling Fins-Cooling fins keep heat away from the cylinder block by increasing the surface area of the cylinder block and contacting the already existing cooler air for cooling efficiency.

21. Crankshaft
Throw-measurement from the center of the crankshaft to the center of the crankpin journal. Determines the stroke of an engine. Throw = ½ stroke.
Crankshaft-converts the linear motion of the piston into rotary motion.
Counterweights-balances the forces of the reciprocating piston and reduces the load on crankshaft bearing journals.
Crankgear-interlocks with the cam gear to turn the crankshaft

22. Crankshaft Magneto Journal PTO Journal Bearing Journal
Crankpin Journal-attaches the connecting rod to the crankshaft
Magneto Journal
PTO Journal
Bearing Journal

23. Piston
Rings
Skirt
Piston Head
Piston Pin Bore

24. Piston Rings
1. Compression Ring-seals the combustion chamber from any leakage during the combustion process.
2. Wiper Ring- used to further seal the combustion chamber and to wipe the cylinder wall clean of excess oil.
3. Oil Ring-Wipes excess oil from the cylinder wall during piston movement. Openings in the ring returns the excess oil to the engine block.

25. Ring Grooves
Ring Lands

26. Crankpin Journal Bearing Surface
Connecting Rod-transfers motion from the piston to the crankshaft and functions as a lever arm
Piston Pin
Piston
Piston pin Bearing Surface
Crankpin Journal Bearing Surface
Rod Cap

27. Valve Tappets
Valve Tappets-Rides on the camshaft and pushes the bottom of the valve stem to open the valve

28. Cam Shaft- includes cam gear and cam lobes; driven by the crankgear
1. Cam Gear-portion of the camshaft that interlocks with the crankgear.
2. Cam Lobes- egg-shaped protrusion on the camshaft that moves a tappet to open a valve; controls the lift and duration of the opening and closing of the valves
Timing Mark

29. Intake Valve- allows the air-fuel mixture to flow into the cylinder
Valve Spring
Valve Retainer
Valve Stem
Valve Head
Intake Valve- allows the air-fuel mixture to flow into the cylinder
Exhaust Valve- allows exhaust valves to flow out of the cylinder

30. Flywheel
Flywheel Nut

31. Magneto
Spark Plug Wire
Armature
Magneto

32. Air Filter

33. Carburetor
Carburetor- provides the proper mixture of air and fuel to the intake valve

34. Intake Manifold

35. Muffler
Muffler Guard

36. Breather Assembly
Breather Cover

37. Shields
Cylinder Shield

38. Dipstick

39. Starter Housing

40. Gas Tank

41. Blower Housing Cover