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This guide provides an overview of small engine parts including the crankcase, cylinder block, piston, valves, camshaft, and more. Learn about their functions and how they work together to power your engine.
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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
Engine Block 2. Cylinder Block 2. 1. 1. Crankcase 3. 3. Crankcase Cover
Cylinder Block 1. Cylinder Bore 1. Head gasket goes here 4. 3. Cooling Fins 3. 2. Valves 2.
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 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
Crankshaft Crankpin Journal-attaches the connecting rod to the crankshaft PTO Journal Magneto Journal Bearing Journal
Piston Rings 1. 2. Skirt Piston Head 4. 3. Piston Pin Bore
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.
1. 2. Ring Grooves Ring Lands
Connecting Rod-transfers motion from the piston to the crankshaft and functions as a lever arm Piston Pin 1. 2. Crankpin Journal Bearing Surface Piston Piston pin Bearing Surface Rod Cap
Valve Tappets Rides on the camshaft and pushes the bottom of the valve stem to open the valve
Cam Shaft- includes cam gear and cam lobes; driven by the crankgear 1. Cam Gear-portion of the camshaft that interlocks with the crankgear. 4. 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 2. Timing Mark 3.
5. 6. Valve Spring Valve Retainer Valve Head Valve Stem 3. 4. 2. 1. Intake Valve- allows the air-fuel mixture to flow into the cylinder Exhaust Valve- allows exhaust valves to flow out of the cylinder
1. Flywheel Flywheel Nut 2.
1. Magneto 2. Spark Plug Wire Armature 3.
Carburetor Carburetor- provides the proper mixture of air and fuel to the intake valve
Muffler Guard
Breather Assembly Breather Cover
