Small Engines / Outdoor Power Equipment Riverside FFA Ag Engineering

Objectives Define a small engine Uses of a small engine History of the small engine Types of small engines Commonality of small engines Engine Cycles Different groups of small engines Basic Parts

Small Engine – an engine that produces power by burning a fuel into a mechanical force that is rated under 25hp II. Equipment used - lawn mowers, weed eaters, snow-mobiles, 4-wheelers, mopeds 2 types of Engines A. External Combustion Engines – (1680) by Christian Huygens - Burning of fuel takes place outside the cylinder and piston B. Internal Combustion Engines- (replaces ECE in 1800’s) - Burning of fuel takes place inside the engine

History 1680 was the first small engine External Combustion Engine- it derives heat from the combustion of water into steam that in turns powered the pistons inside the engine. Ex. Steam engines What are some problems with this engine? Large, not as efficient, very heavy

History Internal Combustion Engine – Burned fuel inside the engine. Adv. More efficient, power, reduced size & weight Ex. Cars, lawnmowers

Small Engines What is an engine – Changes fuel & air into power by spark or compression 1. Fuel & Air is burned to create an expanded gas 2. Expanded gas creates power 3. Power is used for mechanical energy

What is a Cycle? – A sequence that occurs over and over again 2 Types of Internal Combustion Engines Cycles A. 4-cycle B.) 2 - cycle A.4 Cycle Engine – name implies, operates on a series of 4 strokes or piston movements per cycle B.2 Cycle Engine - name implies, operates on a series of 2 strokes or piston movements per cycle

Strokes of an Engine  What is a stroke? –  The movement of the piston from top to the bottom of the cylinder.  What strokes do all engines have in common? 1. Intake 2. Compression 3. Power 4. Exhaust What is TDC, BDC & Bore ? TDC - Top Dead Center BDC - Bottom Dead Center Bore – width of the cylinder Engine displacement is determined by the bore and stroke. D=.7854xB2 x S  Operations of a 4 Cycle Engine Watch this animation

How a 2 cycle engine works How a 2 cycle engine works 1. Intake 2. Compression 1. Power 2. Exhaust  Watch these animations  nes.com/twostroke.html nes.com/twostroke.html nes.com/twostroke.html  om/video/x4u1cr_two- stroke-cycle-engine_tech om/video/x4u1cr_two- stroke-cycle-engine_tech om/video/x4u1cr_two- stroke-cycle-engine_tech 2 strokes engines combine these 2 cycle operations in one stroke

Engines Engines consist of 5 basic parts 1.Block – holds all of the parts 2.Piston 3.Cylinder 4.Crankshaft 5.Camshaft Engines consist of 5 different categories 1.Type of Ignition System 2.# of Strokes 3.Shaft Orientation 4.Cooling System 5.Cylinder Design 4 things ALL small engines for them to work 1.Fuel 2.Spark/heat 3.Compression 4.Air

A. Pull Start B. Electronic C. Combination

WWhat is this?? - The axis of the CRANKSHAFT Two Options 1. Vertical 2. Horizontal Selected for efficiency in driving components Ex. Push lawn mower – Vertical Snow blowers – Horizontal

 How is an engine cooled? 1. Air – air fins 2. Water – radiator Small Engine Efficiency 30% Efficient 30% loss due to exhaust 10% loss due to friction 30% loss due to heat lost to cooling air

Cylinder Design  What way can cylinders come?  Automobiles are multi-cylinders and are called V-6 or V-8  Why do we use the V option for cars/trucks More Power than horizontal or vertical I

1. Crankcase Small Engine Parts Four-Cycle Revised May 2007

Engine Block Crankcase 2. Cylinder Block Crankcase Cover Cylinder block – Where the cylinder & piston is located & combustion takes place. Valve train is attached cylinder block Crankcase – houses most of the parts - cam, crankshafts, oil, & tappets. Main Bearing Journal

Key Terms Piston – moving part within the cylinder Connecting Rod – attached to the bottom of the piston and mounted to the crank shaft Piston Pin – connects the rod to the piston to all allows the rod to move Rod Cap – Connects the connecting rod to the crankshaft Cylinder – where combustion takes place at the top of cylinder & the piston moves up and down in

Key Terms Combustion chamber – where fuel and air ignite in-between the head and piston at TDC Crankshaft – a bar that the middle is bent offset where the connecting rod attaches itself. Flywheel – mounted at the end of the crankshaft – causes the piston to back to he top of the cylinder. Camshaft – allows the valves to open in close in time with the piston.

Part ID Worksheet Piston ID Crankshaft ID Cam Shaft ID Valve System ID How it all works together watch this animation