34 Chapter Small Engine Performance, Maintenance, and Troubleshooting

Chapter Outcomes Explain how engine performance is measured List factors affecting an engine’s suitability for a particular application Demonstrate proper engine maintenance procedures alexkich/Shutterstock.com

Chapter Outcomes Describe the role that service information plays in the service and maintenance of an engine Indentify the three basic things that an engine needs in order to run List the sequence of checks used to systematically troubleshoot an engine Benoit Daoust/Shutterstock.com

Measuring Engine Performance A group of measurements used to determine an engine’s suitability for different applications The amount of work an engine can do in a given period of time and the efficiency with which the engine does that work Areas of measurement include Engine displacement Compression ratio Force, work, and power Horsepower and torque

Measuring Engine Performance Engine displacement The volume of air and fuel the engine can draw into its cylinder(s) during an intake stroke With one cylinder, displacement would be the volume displaced by the piston through its movement from TDC to BDC

Measuring Engine Performance Engine displacement To calculate the displacement of a single cylinder (π/4) × D 2 × L = engine displacement D = cylinder diameter L = length of stroke

Measuring Engine Performance Compression ratio Ratio of the total volume of empty space above the piston at BDC compared to the volume when the piston is at TDC

Measuring Engine Performance Compression ratio Equals the volume above the piston when the piston is at BDC divided by the volume above the piston when the piston is at TDC For example: Volume at BDC = 10 cubic inches Volume at TDC = 1 cubic inch Compression ratio is 10:1 Most small gasoline engines have a compression ratio between 6.5 to 1 and 9.5 to 1

Measuring Engine Performance Force An influence, such as a push or pull, that tends to change the motion of an object Work When force is applied to an object and causes displacement Work = Force × Distance Power The rate at which work is performed in a given time frame

Measuring Engine Performance Horsepower A unit of power equal to 550 foot pounds per second Measurement of work over time Originally developed as a comparison measurement to prove the advantages of machines over animals Torque Rotating or twisting force Equal to force applied across a distance Commonly measured in foot pounds

Engine Selection Criteria to consider Horsepower rating Torque rating Fuel efficiency Crankshaft orientation Physical engine size Fuel system Engine speed controls Lubrication system type Cooling system type TrotzOlga/Shutterstock.com; nikitabuida/Shutterstock.com

Engine Maintenance Crucial for efficient operation and engine longevity Limits malfunctions and breakages Preventive procedures Follow manufacturer guidelines Charles Knowles/Shutterstock.com

Engine Maintenance Lubrication system Check oil level Change oil as needed to keep fresh in system Use viscosity given by manufacturer Use different oil as dictated by location and time of year Nagy-Bogaly Arpad/Shutterstock.com; Goodheart-Willcox Publisher

Engine Maintenance Fuel system Controls air/fuel mixture entering the engine Includes fuel tank, lines, filter, and carburetor Imperative to follow manufacturer’s fuel standards

Engine Maintenance Fuel system Keep tank and motor clean of debris Replace filters at recommended intervals Use manufacturer’s recommended ratios for fuel/oil mixtures for two-stroke engines Drain fuel at the end of season or use fuel stabilizer Keep tank full to minimize condensation in fuel Use minimal ethanol content to prevent damage

Engine Maintenance Air system Keep carburetor, which regulates fuel and air, clean and free of debris Inspect, service, and replace air filters periodically

Engine Maintenance Cooling system Keep engine and radiator clean of dirt and debris Clean radiator fins often or as needed after work Replace coolant as needed Maintain proper antifreeze to water ratio

Service Information Keep manufacturer’s service literature on hand Follow manufacturer’s guidelines for Engine identification procedures Service and repair procedures Service intervals Replacement parts Wear tolerances Carburetor settings

Engine Troubleshooting Systematic diagnosis of engine problems Must follow logical steps 1. Make sure the engine is getting fuel 2. Make sure the engine is getting air 3. Check for spark 4. Check the compression

Engine Troubleshooting Checking the fuel supply 1. Make sure fuel supply is turned on 2. Check for fuel in the tank 3. Check if fuel is making it through the supply line to the carburetor Make sure fuel filter is not clogged if applicable 4. Check vacuum or electric fuel pump Make sure there is power or vacuum

Engine Troubleshooting Checking the air supply Check air filter Clean by tapping out debris Replace if needed

Engine Troubleshooting Check the spark using a spark testing tool If spark appears in the tester, the spark plug may be damaged Check air gap in the plug Replace if necessary

Engine Troubleshooting If there is no spark Check the air gap between flywheel and armature Ensure flywheel key is present Make sure all safety switches are correct Test armature or ignition module Spark plug wire Connected to engine Tester

Engine Troubleshooting Checking the compression At TDC, pressure must be present to ignite fuel Use a compression gauge to test through spark plug hole Compare to published data Perform a leak-down test if needed Use a flywheel bump test

Engine Troubleshooting Common causes for compression loss Loose spark plug or missing compression washer Loose cylinder head bolts Blown head gasket Bad valve seat or face clearance Insufficient lifter/tappet clearance Warped cylinder head Worn cylinder walls Worn or broken piston rings

Engine Troubleshooting Checking the carburetor Make sure linkages are correct and in place Make sure choke and throttle open and close as they should Check governor Do a full disassembly and cleaning according to the manufacturer Replace damaged parts

SAE Connection Small Engine Troubleshooting and Repair Do you like working with small engines? Consider an SAE focused on servicing and repairing small engines, including Weed trimmers Lawn mowers Rotortillers Chain saws Recreational vehicles