Information
ZEXEL
407990-6172
4079906172
Rating:
Cross reference number
Zexel num
Bosch num
Firm num
Name
407990-6172
75AM CONTROL UNIT;BCU
Information:
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,
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,