Down Circuit - Mercury 40 Service Manual

Trim Down
When the trim switch is activated in the down position, the electric motor (c) will rotate the
oil pump gears (j) in the opposite direction. With the oil pump gears rotating backwards, the
flow of oil is reversed. Oil is drawn through the filter (g), through the down circuit suction port
(k) and into the oil pump gears (j). The pump forces pressurized oil into the down passages,
oil will slide the shuttle valve (m) into the up circuit pressure operated valve (n). The shuttle
valve will mechanically open the up circuit pressure operated valve and allow oil, from the
up cavity of the trim cylinder (w), to return into the oil pump. This returning oil, from the up
cavity, will supply the oil required for the down circuit. The oil is blocked from returning into
the reservoir by the ball (i) inside the up circuit suction port. Oil, under pressure, opens the
down circuit pressure operated valve (f) and enters the down passages inside of the man-
ifold (q). The manifold passage connects into the trim cylinder passage leading to the top
of the cylinder. The cavity, inside the cylinder, above the shock piston (u) is the down cavity.
As the down cavity fills with oil, the trim rod (a) retracts into the cylinder, lowering the out-
board motor. Oil from the up cavity exits the cylinder and is drawn back into the pump
through the open up circuit pressure operated valve (n). When the trim rod reached full trav-
el, the oil pressure inside the down circuit will rise until the down circuit pressure relief valve
(e) opens, bypassing oil back into the reservoir. When the trim button is released, and the
oil pump stops supplying pressure, both of the pressure operated valves (f & n) will close
and; if open, the down circuit pressure relief valve (e) will close. The closed valves will lock
the fluid on either side of the shock piston (u) & memory piston (t), holding the outboard mo-
tor in position.
a -
b -
c -
d -
e -
g -
h -
k -
m -
n -
o -
p -
q -
s -
u -
v -
w -
90-828631R3 MARCH 1999
Trim Rod
End Cap
Electric Motor
Reservoir Oil
Down Circuit Pressure Relief Valve
f - Down Circuit Pressure Operated Valve
Filter (2 shown for clarity)
Shock Return Valve
i - Up Circuit Suction Port
j - Oil Pump Gears
Down Circuit Suction Port
l - Oil Fill Cap
Shuttle Valve
Up Circuit Pressure Operated Valve
Manifold Reverse Suction Valve
Manual Release Valve
Manifold
r - Tilt Relief Valve
Tilt Relief Piston
t - Memory Piston
Shock Piston
Impact Relief Valve
Cylinder
POWER TRIM
Page 5C-15