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1. CrankcaseBy Katie Murray, UGA Agriculture Education
Edited by Georgia Agriculture Education Curriculum Office
May 2006
Small Engine Parts
Four-Cycle
Revised May 2007
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Engine Block
1. Crankcase
2. Cylinder Block
Crankcase Cover
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Cylinder Block
2. Valves
1. Cylinder Bore
3. Cooling Fins
Head gasket goes here
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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.
Spark Plug
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Crankshaft
Counterweights-balances the forces of the reciprocating piston and reduces the load on crankshaft bearing journals.
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.
Crankgear-interlocks with the cam gear to turn the crankshaft
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Crankshaft
Magneto JournalPTO Journal
Bearing Journal
Crankpin Journal-attaches the connecting rod to the crankshaft
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Piston
Skirt
Rings
Piston Pin Bore
Piston Head
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Piston Rings1. Compression Ring-seals the combustion chamber from any leakage during the combustion process.
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.
2. Wiper Ring- used to further seal the combustion chamber and to wipe the cylinder wall clean of excess oil.
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Ring GroovesRing Lands
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Connecting Rod-transfers motion from the piston to the crankshaft and functions as a lever arm
Rod CapCrankpin Journal Bearing Surface
Piston Pin
Piston pin Bearing Surface
Piston
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Valve Tappets-Rides on the camshaft and pushes the bottom of the valve stem to open the valve
Valve Tappets
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Cam Shaft- includes cam gear and cam lobes; driven by 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
1. Cam Gear-portion of the camshaft that interlocks with the crankgear.
Timing Mark
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Valve Spring
Valve Stem
Valve Head
Valve Retainer
Intake Valve- allows the air-fuel mixture to flow into the cylinder
Exhaust Valve- allows exhaust valves to flow out of the cylinder
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Flywheel
Flywheel Nut
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Magneto
Armature
Magneto
Spark Plug Wire
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Air Filter
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Carburetor
Carburetor- provides the proper mixture of air and fuel to the intake valve
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Intake Manifold
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Muffler
Muffler Guard
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Breather Assembly
Breather Cover
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Shields
Cylinder Shield
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Dipstick
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Starter Housing
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Gas Tank
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Blower Housing Cover