Honda Outboards BF40A/BF50A Service Manual, Page 228Get this manual
HONDA BF35A45A
Shock valve and return valve
The outboard motor is equipped with the shock valve and return valve to protect it and allow it to cruise at designated tilt angleBecause the piston rises and the oil in the upper chamber of the cylinder is pressured when force is applied to the outboard motor from front while cruising at designated tilt angle, the shock valve opens and the oil flows between the free piston, located under the piston, and the piston to absord the impact and thereby to protect the outboard motorWhen the outboard motor is away from the force, the piston lowers by the dead weight of the outboard motor and the thrustThe oil between the piston and free piston flows through the return valve in the piston and enters the upper chamber of the cylinder