Troubleshooting Small Engines by Jason Spurlin 4/10/02 Virginia Tech This presentation has not been edited by the Georgia Curriculum Office.
Interest Approach Bring in a push mower that will not crank and have students try to crank it. l Ask the students if they have ever experienced this frustration at home and if they were able to fix the problem. l Tell students that we are going to spend time identifying and fixing problems for the next few days. l
Systematic Troubleshooting PERFORMANCE OBJECTIVE On a unit test, describe systematic troubleshooting on small engines with at least 70% accuracy. ENABLING OBECTIVES Explain the principles of systematic troubleshooting. l Identify the fundamental operating requirements of small engines. l Use service manuals and troubleshooting guides to locate tolerances, clearances, and specifications. l
Systematic Troubleshooting l System of testing one component after another until the problem is located and repaired. l BASIC PRINCIPLES 1. Look for the easiest things first. 2. Verify the five fundamental operating requirements. 3. Write down what you have done
Fundamental Operating Requirements 1. 2. 3. 4. 5. Proper Carburetion – correct proportion of clean, fresh fuel has to mix with combustion air Correctly operating ignition system – strong ignition spark must be timed properly Adequate Lubrication – correct amount of clean oil must coat engine components Sufficient cooling – air that reaches engine should be less than 20 o. F hotter than ambient air. Proper compression – at least 30 -45 psi for starting and 90 psi during operation
Check Easiest Things First l Is there clean, fresh fuel in the tank? – Fuel shouldn’t be more than 1 month old Is the spark plug wire connected? l Is the oil level correct? l Gather pertinent information from the owner. l – How was the engine acting before it stalled? – Did it start back? If so, how long before it did? – Did you hit an obstruction during operation?
Eliminate Operating Requirements (Listen to the Engine) EXAMPLE l Try to start the engine. – If the engine spins but won’t start, eliminate lubrication. – While spinning the engine, check for sufficient compression. If sufficient, eliminate compression. – If engine stalls but doesn’t restart after it cools, eliminate cooling system. – Now you can focus on carburetion and ignition. l Once you have eliminated as many systems as possible, refer to a troubleshooting guides and service manuals to pinpoint and solve the problem.
Troubleshooting Guides Tables that have common problems, causes, and remedies listed in an easy to read format l Example information in a troubleshooting guide: l
Cause Effect Engine Fails to Start or Start with Difficulty No fuel in tank Obstructed fuel line Spark plug fouled Fill tank with fresh fuel Clean fuel screen and line Clean and regap spark plug Engine Misses Under Load Spark plug porcelain cracked Faulty condenser Improper carburetor adjustment Replace spark plug Check condenser on a tester and replace if necessary Adjust carburetor Engine Overheats Engine improperly timed Time engine Air flow obstructed Clean shrouds and screens
Service Manuals Service manuals are engine specific l Include service procedures and most common problems l Show exploded views of components that help during reassembly l Provide charts that list proper tolerances, clearances, and specifications l
Summary Troubleshooting is a process of elimination l Check easiest things first. l – Is fuel in tank? – Is spark plug wire connected – Ask owner how the engine is performing Verify the 5 fundamental operating requirements: carburetion, ignition, lubrication, cooling, compression. l Use troubleshooting guides to locate problem. l Use service manuals to locate tolerances, clearances, and specifications. l Write everything down that you check. l
Troubleshooting Engine Systems PERFORMANCE OBJECTIVE On a lab project, perform systematic troubleshooting of the electrical, lubrication, cooling, fuel, and compression systems with at least 70% accuracy. ENABLING OBJECTIVES l l l l Identify symptoms of malfunctioning system components. Inspect spark plug, flywheel key, and magneto. Inspect and repair components of lubricating system. Inspect, clean, and repair cooling fins, flywheel, and air shroud. Inspect fuel tank, fuel pump, carburetor, reed valves (in twocycles), fuel lines, filters, and air cleaner. Inspect governor and adjust if necessary. Identify and repair causes of poor compression.
Ignition System Engine won’t Start Cause Remedy Disconnected spark plug wire No spark at plug Spark plug porcelain cracked Spark plug fouled Faulty magneto Sheered flywheel key Connect wire check switches and magneto replace plug clean and regap check air gap, if necessary overhaul mag. replace flywheel key Engine Misses under Load Fouled Plug Porcelain cracked Improper spark plug gap Pitted breaker points Faulty condensor clean and regap replace plug regap replace points check on a tester, replace if necessary
Ignition cont. Engine Lacks Power Magneto improperly timed reset air gap Engine Runs Unevenly Intermittent spark at plug Other ignition problems: • rust on iron plates • faulty magnets check switches, check magneto for loose or damaged wires
Armature air gap too large Disconnected spark plug wire Burned plug
Lubrication System Lack of Lubrication Causes: – Engine to miss under load Fill crankcase to – Lack of power proper level and/or check oil slinger – Overheating l Engine uses excessive oil – oil level too high Drain oil to proper level – oil filler cap loose of gasket damaged > replace gasket – oil passages obstructed > clean oil passages l
Cooling System A malfunctioning cooling system will cause the engine to overheat l When checking cooling system look for: l – obstructed air flow – clogged cooling fins – broken flywheel vanes – damaged or removed shroud – low oil level
Broken air fin Clogged air passages
Fuel System Fuel system has to deliver clean, fresh, and properly proportioned fuel/air mixture to combustion chamber. Engine Fails to Start Cause No fuel in tank Shut-off valve closed Obstructed fuel line Tank cap vent obstructed Water in fuel Overchoked Improper carburetor adjustment Primer bulb busted Remedy Fill tank Open valve Remove and clean fuel line Open vent Drain tank and refill with clean fuel Close shut off valve and pull cord until engine starts Adjust carburetor Replace primer bulb
Fuel System cont. Engine Misses Under Load Improper carburetor adjustment Reed valves stuck Adjust carburetor Clean or replace reed Engine Lacks Power Choke partially closed Improper carburetor adjustment Air cleaner dirty Reed fouled (2 cycle) Improper fuel/oil mixture (2 cycle) Open choke Adjust carburetor Clean or replace air filter Clean or replace Drain tank; fill with proper mixture Engine Surges or Runs Unevenly Fuel tank cap vent hole clogged Governor parts sticking or binding Carburetor throttle linkage or throttle shaft binding or sticking Improper carburetor adjustment Dirty Carburetor Open vent hole Clean and repair if necessary Clean, lubricate, or adjust linkage Adjust carb Clean carburetor
Intact Primer Bulb Clean Air Filter Clean Carburetor Fuel Line
Most new carburetors do not have needle valves and cannot be adjusted, but many old types are still in operation.
Compression System The following are symptoms of poor compression. – Engine will not start – Engine knocks – Engine misses under load – Engine lacks power – Engine uses excessive oil l Common causes of poor compression. – Damaged or removed crankcase gaskets – Carbon deposits in combustion chamber – Weak valve springs – Leaking valves – Cracked porcelain on spark plug – Excessive cylinder and piston wear l
Burnt valve Chipped piston Missing head gasket
Checking Compression l An engine with proper compression will have a degree of resistance when the operator pulls on the starter rope l Use a compression tester – 30 -45 psi min. for starting – 90 psi min. for efficient operation
Other Ailments l Clogged exhaust system – Insects frequently build nests in exhaust pipes l Associated equipment malfunctioning
Summary l Once you have checked the easy things, work through the each system until you find the problem l Faulty ignition systems can be eliminated if there is spark at the plug. If not, focus attention on magneto, connecting wires, plug, and the flywheel magnets. l A faulty cooling system will cause the engine to overheat and stall, but cooling problems can be easily alleviated by making sure air passages and cooling fins are clean and intact.
Summary cont. l The fuel system has to allow a CLEAN, proper fuel/air mixture to reach the combustion chamber. Make sure that fuel lines and filters are clear and that the carburetor is adjusted properly. l Poor compression is easily identified by resistance when rope starting and by using a compression tester. Problems are generally associated with leaky gaskets, leaking valves, and excessive cylinder wear. l Clogged exhaust systems also prohibit an engine from running properly. l REMEMBER: Check off each thing that you have checked and/or repaired.