Honda BF35A-BF45A Outboard Motors Shop Manual., Page 228Get this manual
Shock valve and return valve The outboard motor is equipped with the shock valve and return valve protect it and allow it 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 absord the impact and thereby 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