Mercury 15 EFI FourStroke, Service Manual

Page: 276 / 406

Tilt Circuit - Down
When the down circuit is activated, the electric motor rotates in the opposite direction. As the pump’s gears rotate, fluid is
drawn through a check valve and into the pump’s inlet. The pump flow passes through a check valve and to the top of the tilt
cylinder. The fluid pushes the cylinder piston down and lowers the engine. Oil, from the bottom side of the cylinder, returns to
the inlet side of the pump. As the tilt cylinder retracts to its limit, down pressure is limited by an orifice in the down pressure
circuit.
Trail Over System
Should the outboard motor strike a submerged object while in forward motion, hydraulic pressure on the top side of the cylinder
will increase to cause the impact relief valve in the tilt cylinder to open. This allows the lower unit to trail over the obstruction.
The fluid in the top side of the cylinder opens the impact relief valve and flows into the cavity between the memory piston and
the cylinder piston. When the lower unit clears the submerged object, the thrust of the engine forces the engine back down. As
the cylinder piston is lowered, fluid trapped between the memory piston and the cylinder piston escapes through a return check
valve. Fluid below the memory piston is trapped in place, therefore, stopping the cylinder piston and returning the outboard to
its previous tilt position.
Power Tilt Features and Operation
Power Tilt
Models equipped with power tilt allow the operator to use the tilt switch to adjust the tilt position of the outboard from full down
to full up. This tilt system is designed to be adjusted when the engine speed is at idle speed or with the engine turned off. At low
idle speed, the outboard can be tilted up to permit shallow water operation.
a - Remote control tilt switch
b - Panel mount tilt switch
c - Tiller handle tilt switch
d - Cowl‑mounted tilt switch
Manual Tilt Release
If the outboard cannot be tilted using the power tilt switch, the outboard can be manually tilted.
NOTE: The manual tilt release valve must be tightened before operating the outboard to prevent the outboard from tilting up
during reverse operation.
Turn out the manual tilt release valve three turns counterclockwise. This allows manual tilting of the outboard. Tilt the outboard
to the desired position and tighten the manual tilt release valve.
31967
Tilt‑in Stop Adjustment
NOTE: The outboard should be positioned against the tilt‑in stop pins during operation.
DN
UP
UP
DN
UP DN
DN
UP
a
b
c
d
DN
UP
32174
Power Tilt
90-8M0125265 eng NOVEMBER 2017 © 2018 Mercury Marine Page 5B-7