Checking tooth contact pattern
on a new gearset.
Paint or coat
12 crown gear teeth with a
marking compound such as
white grease and roll the gear to
obtain a tooth contact pattern
(
Figure 8-97)
. Machine blue, also
called Prussian blue, can be
used. Machine blue is a deep
blue dye mixed in a grease-like
substance. Use a small stiff
bristle brush to apply a light even
coat. A correct pattern should be
well centered on the crown gear
teeth with lengthwise contact
clear of the toe (
Figure 8-98
).
The length of the pattern in an
unloaded condition will be
approximately one-third to two-
thirds of the crown gear tooth in
most models and ratios.
Checking tooth contact pattern
on a used gearset.
Used
gearing will not usually display
the square, even contact pattern
found in new gearsets. The gear
will normally have a pocket at the
toe-end of the gear tooth that
tails into a contact line along the
root of the tooth (
Figure 8-99
).
The more use a gear has had,
the more the line becomes the
dominant characteristic of the
pattern.
Figure 8-97 - Application of a compound
to check tooth contact.
Figure 8-98 - Correct tooth contact pattern
for new gearing.
NAVEDTRA 14050A
8-90
