(1) The pressure of the fingers on the
contacts should be approximately 5 to 6
pounds for the main contacts and 11/2 to
3 pounds for the interlock fingers. The
finger pressure can be measured by
means of a small spring balance attached
to a piece of bent metal strap which can
be slipped under the finger.
(2) If the segment under the fingers is to be
cleaned, do not lift the fingers far enough
off the drum surface so as to strain the
spring and reduce the tension; such a
common source of trouble should be
(3) If the contact fingers and drum segments
are allowed to operate completely dry
they will start to cut in a comparatively
short time. Spread a little light machine
oil occasionally over the drum contacts
with a piece of cloth, and operate the
drum a few times; wipe off any surplus oil
around the contacts or segments.
Oil the drum bearings at intervals with a
(4) The finger pressure is varied by changing
the bend in the finger spring where the flat
Figure 20. Control outline.
spring type finger is used. To increase
the pressure, it is necessary to remove
the finger by removing the screws which
bearings in place and lift out the drum.
hold it in place, and give the spring a little
Next the tap bolts in each cylinder head
greater set. The fingers will maintain their
should be taken out and the head
pressure for a long period of time if they
removed, care being exercised not to
are not abused.
Fingers of the
injure the paper gaskets which are under
compensated type cannot be adjusted for
them. Remove the nut and lockwasher on
spring tension. A damaged finger must
one end of the piston rod, after which the
piston rod with one piston attached can be
c. Cylinder Maintenance.
shoved out of the cylinder by pushing on
the end of the piston rod with a
(1) Pistons are properly oiled when the
screwdriver. The remaining piston in the
reverser is assembled at the factory and
cylinder can easily be pushed out from the
ordinarily will function for a long period
other end. It is not advisable to push the
(six months or a year) before it requires
piston past the opening in the center of
any additional lubrication.
the cylinder as the leather may be injured.
lubrication is necessary, use only oil as
The use of
unsuitable oil will lead to trouble from
88. Magnet Valves
gummed pistons which will cause sluggish
a. General Description.
action or sticking.
(1) The sander and engine shutdown are
(2) In order to remove the piston rod and
provided with magnet valves which
pistons it is necessary to first remove the
four tap bolts which hold the drum