Small Engine Parts FourCycle 1 Crankcase By Katie

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

2. Cylinder Block Engine Block 2. 1. Crankcase 3. Crankcase Cover

Cylinder Block 1. Cylinder Bore 1. 4. 2. Valves 2. Head gasket goes here 3. 3. Cooling Fins

Crankshaft-converts the linear motion of the piston into rotary motion. Crankgear-interlocks with the cam gear to turn the 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. Counterweights-balances the forces of the reciprocating piston and reduces the load on crankshaft bearing journals.

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

Piston 1. Rings 2. Piston Head Skirt 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. Ring Grooves 2. Ring Lands

Piston Pin 1. Piston pin Bearing Surface Connecting Rodtransfers motion from the piston to the crankshaft and 2. functions as a lever arm Crankpin Journal 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 Gearportion of the camshaft that interlocks with the crankgear. 2. Timing Mark 3. 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

5. 6. Valve Spring Valve Retainer 3. 4. Valve Head 1. Exhaust Valve- allows exhaust valves to flow out of the cylinder Valve Stem 2. Intake Valve- allows the air-fuel mixture to flow into the cylinder