Small Engine Troubleshooting

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Small Engine Troubleshooting
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Introduction (Source Small Engines, R Bruce
Radcliff)

• Troubleshooting The systematic elimination of
  the parts of a system or process to locate the
  malfunctioning part(s).

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Five keys to trouble shooting

• Work systematically.
• Never make assumptions.
• Isolate the cause of the problems as quickly as
  possible.
• Analyze all affected factors related to the
  condition.
• Remedy the cause of the problem, not just the
  effect.

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Four (4) Troubleshooting Steps

• Investigation
• Isolation
• Remedy
• Documentation

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Troubleshooting Methods
Easy-likely Split half Quick check Systems Sequent
ial
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Easily-likely

• ELM isolates the cause of a malfunction by
  grouping possible causes as easy, difficult,
  likely and unlikely.
• Once the possible causes have been grouped the
  problem is solved is sequence by identifying the
  easy-likely, easy-unlikely, difficult-likely and
  difficult-unlikely
• Requires good understanding of engine systems and
  previous experience.

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Easily-likely cont. - Example

• A riding lawn mower was used the previous season
  and stored for the winter.
• When the owner attempted to use it in the spring
  it could be cranked, but would not start.

Plugged carburetor
No fuel
Bad plug
Bad coil
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Split Half

• Split Half isolates the cause of a malfunction
  by splitting the system into parts until the
  cause is isolated.

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Split Half cont. - Example

• You are mowing grass with a self-propelled mower
  on a very hot summer day and stop for lunch.
• When you return the mower will not start.
• You check and find the tank has gas.
• What do you do?

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Split Half cont. - Example
No spark
Step one Check for spark at the spark plug.
Good Spark
1. Fuel system 2. Compression system
No or weak spark
Split electrical system into parts and check each
part. Start with easiest. Spark plug
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Split Half cont. - Example
No spark
Step two Remove spark plug from system.
Good Spark
Bad spark plug
No or weak spark
Check another electrical component. Stop
switch/wire
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Split Half cont. - Example
Step three Remove stop switch from system.
No spark
Good Spark
Bad stop switch
No or weak spark
Check another electrical component. Flywheel
magnets
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Split Half cont. - Example
Step four Polish magnet(s).
Good Spark
Engine runs.
No or weak spark
Check another electrical component. Ignition coil
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Split Half cont. - Example
Step five Remove and test Coil.
Note coil must be tested with a special coil
testing machine or with a multi meter.
Good coil
Check for unique problem such as shorted wire,
etc.
No or weak spark
Replace coil
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Quick-check

• Isolates the cause of a malfunction by focusing
  on common problems identified by the
  manufacturer, product history, and/or service
  experience.
• May only be available to service personal.

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Quick-check cont. - Example

• You go home for the weekend and are told that the
  last time the walk behind mower was being used
  the blade hit something and the engine died. No
  one can get it started.

Quick check flywheel key
Anyone that works with B S engine driven lawn
mowers know the they use an aluminum flywheel key
that is designed to shear when the blade strikes
an object. When this occurs the ignition is out
of time.
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Systems approach

• Isolates problems by dividing the engine into
  separate systems and subsystems.
• Five (5) common systems.
• Compression
• Fuel
• Electrical
• Cooling
• Lubrication
• Symptom(s) of engine is traced to system and
  system parts.

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Sequential method

• Starts at one end of a system and tests all of
  the parts, in sequence, until the problem is
  found.

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Sequential Method - Example

• When trying to get an engine to start, your tests
  indicate the engine is not getting fuel to the
  combustion chamber.

• Trouble shooting sequence.
• Fuel tank
• Fuel filter
• Fuel lines
• Carburetor
• Intake valve

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Summary

• The successful troubleshooter uses an analytical
  approach to trace the problem to the engine part
  or parts that are malfunctioning.
• Successful troubleshooters do not rely on any
  single method discussed in the textbook, but
  would develop their own system that would be a
  combination of all of these.

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