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Measuring and Testing Instrument

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					Measuring and Testing
Instruments
Small Engines




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Measuring and Testing Instruments
   Precision measuring instruments are used to
    determine if parts are to be rejected resulting in
    replacement.
   The repair of any gasoline engine should be based
    upon the manufactures recommendations in the
    service manual.
   The listing of clearance or tolerance measurements is
    expressed in .001 of an inch.

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Measuring and Testing Instruments
   For example:
       The spark plug gap might be listed as .030
        meaning for normal operation the gap should be
        gapped at .030 inch.
   Specifications are normally listed for:
       Armature air gap, valve tappet clearance, piston
        to cylinder wall clearance, ring-groove clearance,
        etc…

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Micrometer Caliper
   One of the more common measuring devices is the
    outside micrometer caliper.
   It is designed to measure machined components
    where tolerances are critical as on a crankshaft
    journal.
   The marks on the thimble represent .001 inch each.
   One complete revolution of the thimble equals .025.



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Micrometer Caliper
   Every fourth line on the sleeve is longer than the
    others to help identify the whole numbers which
    represent tenths.
   A number of different types of micrometers are
    manufactured.
   The outside micrometer is the most common and can
    to measure the outside diameter of round objects,
    and the width and thickness of flat pieces.

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Micrometer Caliper
   The inside micrometer is used to measure the
    diameter of a hole such as the inside diameter
    of an engine cylinder.
   The depth micrometer is used to measure the
    depth of holes, grooves, and slots.
   Micrometers are all read in the same manner.


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Micrometer Caliper
   Micrometers usually are designed to measure
    within a 1 inch range.
   0-1 inch
   1-2
   2-3
   Etc…


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Thickness Gauges
   A variety of different gauges are manufactured for
    measuring the clearance or gap between two parts.
   The most common gauges are the flat feeler gauge,
    round wire gauge, reject gauge, and plastigage.
   Some uses of thickness gauges are:
       Spark plug gap, breaker-point gap, connecting rod to
        crankpin clearance, piston ring end gap.



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Thickness Gauges
   The most commonly recognized thickness
    gauge is the flat feeler gage.
   Each blade is a different thickness.
   Each blade is stamped with its thickness.
   Feeler gauges can be used to measure:
       Valve tappet clearance, air gap between the
        armature legs and the fly wheel magnet,
        crankshaft end play.

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Thickness Gauges
     Round-Wire feeler
      gauge
         It has several
          applications for
          working with small
          engines.
         The most common of
          these is measuring the
          electrode gap of new
          or used spark plugs.

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Thickness Gauges
   Plug Gauge
       Commonly used in
        small engine repair.
       Is used to determine if a
        valve guide bushing
        needs replacing.
       Other names given to a
        plug gauge are go, no-
        go, and reject gauges.


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Thickness Gauges
     Plastigage
         Can be used to
          measure clearance
          between the bearing
          journal on a
          crankshaft and its
          bearing or rod cap.
         The rod cap is
          tightened to a
          recommended torque
          measurement the
          flatten plastic is
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          measured.
Torque Wrench
     There are specs for
      the torque to which
      bolts should be
      tightened depending
      upon size and grade.
     Torque equals force
      times distance.
     Torque wrenches are
      usually calibrated in
      feet or pound inches.
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Compression Testing
     Compression testing can help determine if
      the small engine being studied has a
      problem with either the cylinder, piston
      rings, valves and or gaskets.
     Normal engines one cylinder engines will
      have a 60-150 psi rating.
     An accepted rule is that compression
      problems exist if the reading is 20% less
      than the minimum spec for the engine.
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Compression Testing
   Compression testers
    can either have a
    rubber tip which is held
    to the spark plug hole
    or a threaded end for
    screwing into the spark
    plug hole.



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Tachometers
                 Tachometers are used
                  to check the operating
                  revolutions per minute
                  of the engine.
                 Cylinder Testing
                     A telescoping gage can
                      be used to measure
                      cylinder wear.



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