General
Information
1‐18
component. Refer to the following
sections for specific measuring tools.
Feeler Gauge
Use feeler or thickness gauges
(Figure19) for measuring the distance
between two surfaces. A feeler gauge
set consists of an assortment of steel
strips of graduated thickness. Each
blade is marked with its thickness.
Blades can be of various lengths and
angles for different procedures. A
common use for a feeler gauge is to
measure valve clearance. Use wire
(round) type gauges to measure spark
plug gap.
Calipers
Calipers (Figure 20) are excellent tools
for obtaining inside, outside and depth
measurements. Although not as precise
as a micrometer, they allow reasonable
precision, typically to within 0.05 mm
(0.001 in.). Most calipers have a range
up to 150 mm (6 in.).
Calipers are available in dial, Vernier or
digital versions. Dial calipers have a dial
readout that provides convenient
reading. Vernier calipers have marked
scales that must be compared to
determine the measurement. The digital
caliper uses a liquid-crystal display
(LCD) to show the measurement.
Properly maintain the measuring
surfaces of the caliper. There must not
be any dirt or burrs between the tool and
the object being measured. Never force
the caliper to close around an object.
Close the caliper around the highest
point so it can be removed with a slight
drag. Some calipers require calibration.
Always refer to the manufacturer’s
instructions when using a new or
unfamiliar caliper.
The fixed scale is marked in 1 mm
increments. Ten individual lines on the
fixed scale equal 1 cm. The movable
scale is marked in 0.05 mm (hundredth)
increments. To obtain a reading,
establish the first number by the location
of the 0 line on the movable scale in
relation to the first line to the left on the
fixed scale. To determine the
next
number, note which of the lines on
the
movable scale align with a mark on
the
fixed scale. A number of lines will
seem
close, but only one will align
exactly.
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