Stationary Condition; When The Outboard Hits Something In The Water - Yamaha F150B Service Manual

Stationary condition

When the PTT switch is not pressed, the gear pump will not pump the fluid, the up-main valve and
the down-main valve will remain closed, and the PTT unit in the system remains constant. This will
allow the tilt ram and the trim ram to maintain their positions until the PTT fluid flows through the
system again.

When the outboard hits something in the water

If the lower casing comes in contact with an obstacle while the boat is in operation, a sudden exten-
sion force becomes applied to the tilt ram. This force causes the fluid pressure in the tilt cylinder
upper chamber to increase, and the tilt piston absorber to open and release the fluid pressure into
the space between the tilt piston and the free piston. As a result, the damping effect of the tilt piston
absorber and the oil lock mechanism prevent the PTT unit from damage, before the tilt piston comes
in contact with the top of the tilt cylinder.
After the collision, a force to return the outboard motor to its original position is generated due to the
weight of the outboard motor and the thrust of the propeller.
The PTT fluid passes through the shock return valve of the tilt piston, via the free piston, and into the
tilt cylinder upper chamber.
When the tilt piston comes in contact with the free piston, the tilt piston stops.
a
b
A
The outboard motor hit the object.
B
The outboard motor returned to the original
position.
a
Tilt ram
c
d
A
b
c
d
e
f
e
B
Tilt cylinder
Tilt piston absorber
Tilt piston
Shock return valve
Free piston
PTT unit
0
1
2
3
4
5
6
7
8
9
10
f
A
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