SERVICE MANUAL & ICA
8750 AMPHIBIAN/SEAPLANE FLOATS ON CESSNA 208/208B
P/N 1005723 Doc. No. W8750-24-01
Page 58 of 104
Revision C
wheels, adjust the NAS-428 bolt to lightly
make contact with the Main Gear Top Arm
when the gear is in the full down position,
then turn the bolt one and a half turns in so
that the bolt no longer makes contact with
the Top Arm. Gap should be about 0.050
inches. Tighten the jam nut.
NOTE:
There are three “over center” locks on
the main gear when the gear is down. The first
is the over center rod linkages that are adjusted
in the above steps. The second is from the
spring pulling on the actuator arm when the gear
is in the down position. The spring prevents the
actuator from moving in the event of a loss of
hydraulic pressure. The third comes in the form
of the angle between the oleo-pneumatic shock
strut and the Top Arm Assembly. The vector of
the oleo force is “over center”, about at the
rotation point on the Top Arm Assembly. Thus,
one could effectively remove the entire gear
actuator, and the geometry of the Oleo and the
Top Arm alone would force the contact faces of
the top arm and top mount together and lock it
“over center.”
There are also two “over center” locks when the
gear is in the retracted “UP” position. The first
is a spring installed on the actuating arm that
prevents motion of the rack and pinion actuator
in the event of a hydraulic failure. The second
over center lock comes from the geometry of the
gear in the up position.
Since the retraction mechanism is driven over
center, the weight of the landing gear and oleo,
when retracted, prevent the retraction
mechanism from rotating past the over center
point. The weight of the gear wants to rotate the
Top Arm Assembly, however, when rotating the
Top Arm, the rod linkages must also move. The
geometry is such that the rod linkages are “over
center” on the actuator shaft centerline, and thus
the rod linkages are trying to rotate the actuator
more toward the “UP” position and in turn force
the actuator piston face into the up adjustment
setscrew.