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The bore needs
a burr- and nick-free chamfer to
prevent damage to the seal’s outside
diameter (O.D.) during installation. A proper chamfer
creates what is known as a pilot gap. The pilot
gap is one half the difference between the diameter
of the leading edge of the seal O.D. chamfer and
the housing
bore I.D. A
positive gap ensures that the seal O.D. makes proper
contact with the bore chamfer prior to actually
entering the bore, thus facilitating proper installation.
A negative (or nonexistent) gap would create excessive interference and
prevent the seal O.D. from aligning properly with
the bore chamfer, thus hindering proper installation
and likely causing damage to the seal O.D. Examples
of positive pilot gaps are shown in Figure
137.
Chamfering
also reduces the force required for proper assembly,
helps prevent seal misalignment (cocking),
and minimizes case distortion.
As shown in Figure 138,
the chamfer should be between 0.060" and 0.090" long
and angled from 15° to 30°. Recessed bores
should also have a 0.030" radius at the back
of the bore. Both the ISO and
RMA recommendations
regarding bore depth, chamfer length, and corner
radius are listed in Table 46.
THE
BORE MAIN PAGE
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“Good
design doesn’t stop with the shaft seal
and the shaft. Due consideration must also
be given to the housing bore.”
Figure 137
Figure 138
Table 46
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