Mercury 225 EFI, Service Manual

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POWER TRIM - DESIGN II
Page 5B-18 90-884294 OCTOBER 2001
Trail Over System
Should the outboard motor strike a submerged object with light steady pressure, while in
forward motion, oil will build up sufficient pressure in the top of the tilt cylinder (4) to open
the piston trail over relief valve (7) (600 psi). Oil on the bottom side of the cylinder is locked
in by the up circuit pressure operated valve (1) and manual tilt valve (3). Therefore, the
piston trail over relief valve allows the oil from the down side cavity of the trim cylinder to
pass through the piston trail over relief valve, into the area between the
tilt ram piston (5)
and the memory piston (6). The return valve (8) allows the oil to return through the piston,
back to the down side cavity as the outboard returns to its normal running position. Propel-
ler thrust and the weight of the outboard provides the return motion for the engine.
Shock System
When a submerged object is hit with great force, oil will build up sufficient pressure in the
top of the tilt cylinder (4) to open both the trail over valve and the piston impact relief valves
(7) (3200 psi). Oil on the bottom side of the cylinder is locked in by the up circuit pressure
operated valve (1) and manual tilt valve (3). Therefore, the piston impact relief valve al-
lows the oil from the down side cavity of the trim cylinder to pass through the piston impact
relief valve, into the area between the
tilt ram piston (5) and the memory piston (6). The
return valve (8) allows the oil to return through the piston, back to the down side cavity
as the outboard returns to its normal running position. Propeller thrust and the weight of
the outboard provides the return motion for the engine.