Small Engine Parts
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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. Engine Block. 2. Cylinder Block. 1. Crankcase. Crankcase Cover. Cylinder Block. 1. Cylinder Bore. Head gasket goes here.

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1. Crankcase

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Small Engine Parts


By Katie Murray, UGA Agriculture Education

Edited by Georgia Agriculture Education Curriculum Office

May 2006

1. Crankcase

Engine Block

2. Cylinder Block

1. Crankcase

Crankcase Cover

Cylinder Block

1. Cylinder Bore

Head gasket goes here

3. Cooling Fins

2. Valves

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

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


Crankpin Journal-attaches the connecting rod to the crankshaft

PTO Journal

Magneto Journal

Bearing Journal




Piston Head

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.

Ring Grooves

Ring Lands

Connecting Rod-transfers motion from the piston to the crankshaft and functions as a lever arm

Piston Pin

Crankpin Journal Bearing Surface


Piston pin Bearing Surface

Rod Cap

Valve Tappets

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.

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

Valve Spring

Valve Retainer

Valve Head

Valve Stem

Intake Valve- allows the air-fuel mixture to flow into the cylinder

Exhaust Valve- allows exhaust valves to flow out of the cylinder


Flywheel Nut


Spark Plug Wire



Air Filter


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

Intake Manifold


Muffler Guard

Breather Assembly

Breather Cover


Cylinder Shield


Starter Housing

Gas Tank

Blower Housing Cover

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