(courtesy of PlastigaugeUSA.com)
Plastigauge is a great product for checking bearing clearance in your
engine or any place where measuring a hidden clearance is required.
It's also used for numerous industrial applications. It is comprised
of a rod or thread of a compliant plastic material of accurately determined
cross-section - either circular or square.
The surfaces between which measurement is to be made are first separated,
Plastigauge is inserted (see fig. 2) and the surfaces are returned to
their standard position.
. It is recommended that surfaces be clean prior to use of Plastigauge
Fig.2 . Plastigauge placed across the bearing surface
The once circular (or square) section will have been flattened but the
area of the cross-section will remain unchanged. We can, therefore,
or in the case of a square section of side 'a' :-
Here T, the clearance to be measured is equal to a constant divided
by the width of the strip after deformation. By opening the surfaces
to reveal the deformed gauge, W can be measured directly and from this
the clearance, T, can be determined.
3 De-formed Plastigauge ready for measurement
In practice the need for this calculation is obviated by the use of
a calibrated scale on which an array of marks has been printed (see
Fig 4. De-formed Plastigauge compared with calibrated scale.
The width of the strip can be compared with the scale (see fig. 4).
The actual clearance is shown alongside the mark which most nearly corresponds
to the width. For greater accuracy the clearance may be interpolated
between the two most nearly comparable scale marks.
is highly effective for measuring the clearance in almost any bearing
configuration or area that has hidden surfaces.
Shaft end-float lends itself to direct measurement by Plastigauge.
Flatness and clearance in pipe-flanges and cylinder heads are readily
checked and measured with standard Plastigauge.
It is recommended that the surfaces be separated by a ground spacing
washer or shim of (typically) 0.002". The gauge is positioned
in those regions where distortion is suspected and any variations of
flatness will be shown, after the assembly is dismantled, by variations
in the width of the compressed strip.
For large bearings, multiple measurements are recommended by inserting
two or more gauges around the bearing.
Plastigauge is particularly effective for the measurement of separation
in moulding tools, and wherever it is required to determine the separation
between hidden surfaces.
widely used application
most widely used application of Plastigauge is in the measurement of
clearance in plain automotive bearings. This application is described
Remove the engine sump cover to reveal the big-end and its retaining
set-screws. Remove surplus oil and release the big-end shells by unscrewing
the set-screws. Apply a smear of grease to the journal and small quantity
of silicone release agent to the shell.
Trim a length of Plastigauge to fit across the journal using the grease
to hold it in place. Replace the shell and tighten the set-screws to
the recommended torque setting - without rotating the journal.
Now remove the shell to reveal the Plastigauge which will have been
spread across the bearing surface as a stripe or band. Match the width
of the stripe against the calibrated gauge card supplied and read off
Ideally you should remove the Plastigauge stripe with a clean oily cloth
or industrial de-greasing solvent, but users may be assured that any
Plastigauge left behind is oil soluble and cannot harm the engine in
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You can buy individual packs or boxes for commercial and
industrial applications or purchase smaller packs at the
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