921513-0612 Tohatsu SCREW

Components of the Compression Brake
Illustration 1 g00318128
Installed Compression Brake (1) Rear housing. (2) Front housing. (3) Stud. (4) Support bracket. The compression brake consists of two different housings. Both brake housings are installed in the compartment for the valve mechanism above the rocker arms and the rocker arm shaft. Each brake housing is positioned over three cylinders. Each brake housing is mounted on a support bracket (4) at the end of the rocker shaft brackets. Special adjustment screws for the exhaust rocker arm and exhaust valve bridges are necessary. Note: The operation of the compression brakes only uses the exhaust side of the engine valve mechanism.A spacer is used between the cylinder head and the valve cover for the installation of the valve cover. With an installed compression brake, this increase in height is 90 mm (3.5 inch). The front compression brake housing and the rear compression brake housing consist of the following parts:
Three master pistons
Three slave pistons
Three control valves
One solenoid valveEngine Compression Brake's Operation
Illustration 2 g00322183
Master-Slave Circuit Schematic (1) Solenoid valve (2) Spring (3) Control valve (4) High pressure oil passage (5) Slave piston adjustment screw (6) Master piston (7) Spring (8) Rocker arm adjustment screw (9) Rocker arm (10) Slave piston (11) Exhaust pushrod (12) Exhaust valves (13) Ball check valve (14) Oil passage from manually operated control switch (15) Low pressure oil passageThe compression brake operates with engine oil. The engine oil is supplied from the rocker arm shafts. Solenoid valve (1) controls the oil flow in the brake housing. When the solenoid is activated, solenoid valve (1) moves down. The downward movement of the solenoid valve closes the oil drain passage to the oil pan. At the same time, solenoid valve (1) opens low pressure oil passage (15) to three control valves (3). As low pressure passage (15) is filled with engine oil, control valves (3) are pushed up in the chamber against the force of spring (2). At this position, a groove in control valve (3) should align with high pressure oil passage (4). This oil passage supplies high pressure oil to slave piston (10) and master piston (6). The engine oil pressure will now lift ball check valve (13). The engine oil pressure also fills high pressure oil passage (4) and the chambers behind the pistons (master-slave circuit). This pressure moves the pistons downward. Then, the pistons can contact the engine valve mechanism. When the oil pressure is the same pressure through all the oil passages, the small spring will force ball check valve (13) against the seat of the ball check valve. The system is completely pressurized, and the system is ready for operation with the engine valve mechanism. When the solenoid is activated, the compression brake is ready to operate in approximately 1/5 of a second.
Illustration 3 g00318164
Oil Passage Schematic (Front Housing) (1) Solenoid valve. (3) Control valves. (4) High pressure oil passage. (6) Master pistons. (10) Slave pistons. (15) Low pressure oil passage.When engine pushrod (11) for the exhaust valve begins to move up on the normal cycle of the exhaust valve, the following two components can make contact with master piston (6) :
Rocker arm (9)
Rocker adjustment screw (8) As master piston (6) begins to move up, the oil pressure increases in passage (4). The pressure increases because ball check valve (13) will not allow the oil to escape. Since there is a constant increase in pressure with the rocker arm movement, slave piston (10) is pushed down with enough force to open exhaust valves (12). The master-slave circuit is designed so that master piston (6) is moved only by an engine cylinder on the exhaust stroke. At the same time, slave piston (10) opens only the exhaust valves of an engine cylinder on the compression stroke. This occurs just before the cylinder arrives at the top center position. The braking force is constant, and the sequence is the same sequence as the firing order of the engine. See Table 1.
Table 1
Relationship of the Master-Slave Circuit    
Location of Master Piston     Location of Slave Piston    
Sequence for Activation    
No 1 Pushrod     No 3 Pushrod    
No 5 Pushrod     No 6 Pushrod    
No 3 Pushrod     No 2 Pushrod    
No 6 Pushrod     No 4 Pushrod    
No 2 Pushrod     No 1 Pushrod    
No 4 Pushrod     No 5 Pushrod    When solenoid valve (1) is in the OFF position, the engine oil supply passage is closed, and the oil drain passage to the oil pan is opened. This drains the oil beneath the control valve (3). Spring (2) pushes control valve (3) to the bottom of the chamber. This position allows the oil from high pressure oil passage (4) to drain into the chamber above the control piston. Spring (7) now moves master piston (6) up to the NEUTRAL position of the master piston and away from rocker arm adjustment screw (8). The time that is necessary for the system to stop operation is approximately 1/10 of a second. The compression brake will not be able to operate now until the solenoid is activated again.Controls for the Compression Brakes
Illustration 4