Transcript Measuring and Testing Instruments

Measuring and Testing
Instruments
Small Engines
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Measuring and Testing Instruments
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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
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For example:
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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:
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Armature air gap, valve tappet clearance, piston
to cylinder wall clearance, ring-groove clearance,
etc…
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Micrometer Caliper
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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
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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
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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
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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
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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:
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Spark plug gap, breaker-point gap, connecting rod to
crankpin clearance, piston ring end gap.
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Thickness Gauges
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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:
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Valve tappet clearance, air gap between the
armature legs and the fly wheel magnet,
crankshaft end play.
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Thickness Gauges
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Round-Wire feeler
gauge
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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
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Plug Gauge
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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, nogo, and reject gauges.
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Thickness Gauges
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Plastigage
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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
measured.
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Torque Wrench
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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
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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
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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
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Tachometers are used
to check the operating
revolutions per minute
of the engine.
Cylinder Testing
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A telescoping gage can
be used to measure
cylinder wear.
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