Troubleshooting Small Engines by Jason Spurlin 41002 Virginia Tech This presentation has not been ed

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Troubleshooting Small Enginesby Jason
Spurlin4/10/02Virginia TechThis presentation
has not been edited by the Georgia Curriculum
Office.
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Interest Approach

• Bring in a push mower that will not crank and
  have students try to crank it.
• Ask the students if they have ever experienced
  this frustration at home and if they were able to
  fix the problem.
• Tell students that we are are going to spend time
  identifying and fixing problems for the next few
  days.

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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.
• Identify the fundamental operating requirements
  of small engines.
• Use service manuals and troubleshooting guides to
  locate tolerances, clearances, and
  specifications.

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Systematic Troubleshooting

• System of testing one component after another
  until the problem is located and repaired.
• BASIC PRINCIPLES
• 1. Look for the easiest things first.
• 2. Verify the five fundamental operating
  requirements.
• 3. Write down what you have done

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Fundamental Operating Requirements

• 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 20oF hotter than ambient air.
• Proper compression at least 30-45 psi for
  starting and 90 psi during operation

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Check Easiest Things First

• Is there clean, fresh fuel in the tank?
• Fuel shouldnt be more than 1 month old
• Is the spark plug wire connected?
• Is the oil level correct?
• Gather pertinent information from the owner.
• 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?

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Eliminate Operating Requirements(Listen to the
Engine)

• EXAMPLE
• Try to start the engine.
• If the engine spins but wont start, eliminate
  lubrication.
• While spinning the engine, check for sufficient
  compression. If sufficient, eliminate
  compression.
• If engine stalls but doesnt restart after it
  cools, eliminate cooling system.
• Now you can focus on carburetion and ignition.
• Once you have eliminated as many systems as
  possible, refer to a troubleshooting guides and
  service manuals to pinpoint and solve the
  problem.

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Troubleshooting Guides

• Tables that have common problems, causes, and
  remedies listed in an easy to read format
• Example information in a troubleshooting guide

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Service Manuals

• Service manuals are engine specific
• Include service procedures and most common
  problems
• Show exploded views of components that help
  during reassembly
• Provide charts that list proper tolerances,
  clearances, and specifications

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Summary

• Troubleshooting is a process of elimination
• Check easiest things first.
• 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.
• Use troubleshooting guides to locate problem.
• Use service manuals to locate tolerances,
  clearances, and specifications.
• Write everything down that you check.

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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
• 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 two-cycles), fuel lines, filters, and
  air cleaner.
• Inspect governor and adjust if necessary.
• Identify and repair causes of poor compression.

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Ignition System
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Ignition cont.

• Other ignition problems
• rust on iron plates
• faulty magnets

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Armature air gap too large
Disconnected spark plug wire
Burned plug
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Lubrication System
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Lubrication System

• Lack of Lubrication Causes
• Engine to miss under load
• Lack of power
• Overheating
• Engine uses excessive oil
• oil level too high
• oil filler cap loose of gasket damaged gt replace
  gasket
• oil passages obstructed gt clean oil passages

Fill crankcase to proper level and/or check oil
slinger
Drain oil to proper level
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Cooling System

• A malfunctioning cooling system will cause the
  engine to overheat
• When checking cooling system look for
• obstructed air flow
• clogged cooling fins
• broken cooling fins
• broken flywheel vanes
• damaged or removed shroud
• low oil level

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Broken air fin
Clogged air passages
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Fuel System
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Fuel System
Fuel system has to deliver clean, fresh, and
properly proportioned fuel/air mixture to
combustion chamber.
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Fuel System cont.
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Intact Primer Bulb
Clean Air Filter
Clean Carburetor
Fuel Line
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Most new carburetors do not have needle valves
and cannot be adjusted, but many old types are
still in operation.
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Compression System
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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
• 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

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Burnt valve
Chipped piston
Missing head gasket
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Checking Compression

• An engine with proper compression will have a
  degree of resistance when the operator pulls on
  the starter rope
• Use a compression tester
• 30-45 psi min. for starting
• 90 psi min. for efficient operation

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Other Ailments

• Clogged exhaust system
• Insects frequently build nests in exhaust pipes
• Associated equipment malfunctioning

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Summary

• Once you have checked the easy things, work
  through the each system until you find the
  problem
• 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.
• 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.

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Summary cont.

• 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.
• 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.
• Clogged exhaust systems also prohibit an engine
  from running properly.
• REMEMBER Check off each thing that you have
  checked and/or repaired.