86776 Mercruiser LATCH

1.1 Air Compressor
The air compressor, installed at the flywheel housing on the left side of the engine, is driven at one-half the engine speed by the air compressor gear that is in mesh with the engine timing gear. A coupling is mounted at the rear end of the crankshaft to drive the injection pump.The aluminum alloy piston has three compression rings and an oil ring.The connecting rod, made also of aluminum alloy consists of connecting rod proper and connecting rod cap, installed in the crankshaft pin with connecting rod bolts.The cylinder head has suction valve, delivery valve and unloader valve installed. For lubrication of the air compressor, refer to Group 12 Lubrication. When the piston moves down, resultant negative pressure causes the suction valve to open, allowing air to be introduced to the cylinder. When the piston moves up, the suction valve spring causes the suction valve to close, compressing air.When the piston moves up, compressed air overcomes the force of delivery valve spring, forcing the valve to open and feeding air to the air tank under pressure. The unloader valve acting with the pressure governor provides adjustment of pressure in the air tank. When the air pressure in the air tank exceeds specified level (pressure governor operating pressure), the pressure governor opens to fed compressed air to the unloader valve to push it down. At the same time, it keeps the suction valve forced open so that the air compressor is run under load free condition.When the air pressure in the air tank drops below specified level, the pressure governor again operates to discharge compressed air from the upper portion of the unloader and the unloader valve is made to return to initial position by the unloader valve spring. Then, the suction valve starts to operate. The cylinder head is either water-cooled or air-cooled by fins in order to prevent overheating by the compression heat of the air compressor.The water-cooled type has coolant led from the oil cooler to cool cylinder head valves. Coolant is then returned to the rear end of the engine cylinder head.1.2 Pressure Governor
The pressure governor controls compressor operation to keep the air tank pressure within specified limits.To the high pressure valve of the diaphragm, the same air pressure as in the air tank acts always through the filter, thereby balancing with the adjusting spring force. When the pressure in the air tank increases to exceed that opening pressure of the high pressure valve, the air forces up the high pressure valve seat of the diaphragm. This causes increase of acting area so that the diaphragm moves up quickly to close the seat of the low pressure valve.When the low pressure valve is closed, air now flows through the valve body to force down the unloader valve of the air compressor, thereby stopping air supply to the air tank.As the air pressure in the air tank gradually drops, the diaphragm is forced down by the adjusting spring and the low pressure valve opens and the high pressure one closes. As a result, the air on the unloader side is exhausted through the exhaust hole and air supply to the air tank is resumed.2. Specifications
3. Service Standards
3.1 Service Standards Table
(1) Air Compressor (2) Pressure Governor 3.2 Tightening Torque Table
(1) Air compressor (2) Pressure governor 4. Special Tool
5. Service Procedure
5.1 Air Compressor
Removal and installation
The removal and installation procedures of the air compressor are same as those of the pump drive case. See Group 13 Fuel and Engine Control.Disassembly
Disassembly(1) Removal of suction valve holder Using special tool, Air Compressor Suction Valve Tool, remove the suction valve holder.(2) Removal of delivery valve holder (Air-cooled type only) Using special tool, Air Compressor Delivery Valve Tool, remove the delivery valve holder.(3) Removal of piston ring Using special tool, Piston Ring Tool, remove the piston ring.Inspection
Inspection(1) Piston to cylinder liner clearance Calculate the clearance and if it exceeds the limit, replace the piston or cylinder liner.(2) Piston ring to ring groove clearance Measure the clearance and if it exceeds the limit, replace the piston ring or piston. Measure over entire circumference of the piston.(3) Piston ring open end gap Fit the piston ring to a new cylinder liner or gauge and measure the open end gap. If the gap exceeds the limit, replace the ring. Push in the piston ring flat by the piston and measure.(4) Piston to piston pin clearance Calculate the clearance and if it exceeds the limit, replace the piston or piston pin.(5) Piston to connecting rod clearance Calculate the clearance and if it exceeds the limit, replace the piston pin or connecting rod.(6) Crankshaft pin to connecting rod bearing clearance Calculate the clearance and if it exceeds the limit, replace the bearing.(7) Connecting rod end play If the end play exceeds the limit, replace the connecting rod.(8) Crankshaft journal to bearing clearance Calculate the clearance and if it exceeds the limit, replace the bearing.(9) Unloader valve assembly If the unloader valve has been worn heavily, replace the unloader valve assembly.Reassembly
Reassembly(1) Installation of delivery valve holder (Air-cooled type only) Using the special tool. Air Compressor Delivery Valve Tool, install the delivery valve holder.(2) Installation of suction valve holder (a) Using special tool, Air Compressor Suction Valve Tool, install the suction valve holder. (b) After tightening the suction valve holder, stake at three places using a punch. Do not stake at area that will be O-ring sealing surface.(3) Installation of connecting rod. Assemble aligning match marks on the connecting rod and connecting rod cap.(4) Installation of piston ring Using the special tool, Piston Ring Tool, install the piston ring. Locate open ends of each piston ring as illustrated above.(5) Installation of air compressor gear Install aligning match marks on the crankshaft and air compressor gear.