Top end overhauls are scheduled according to the recession of the exhaust valve stems. This measurement provides an accurate indication of the rate of valve wear. This measurement can be used to predict when a cylinder head requires replacement. For more information, refer to this Operation and Maintenance Manual, "Valve Stem Projection - Measure/Record" topic.
Note: The generator or the driven equipment may also require service when the engine overhaul is performed.
A top end overhaul involves servicing the cylinder heads and turbochargers. Also, some other engine components are inspected.
Top end overhauls require more tools than preventive maintenance. The following tools are needed for restoring the engine to factory specifications:
- Torque wrenches
- Dial indicators
- Accurate measurement tools
- Cleaning equipment
- Rebuilding equipment
Caterpillar dealers are equipped with these tools. Caterpillar dealers can provide a flat rate price for a top end overhaul.
Unexpected problems may be found during a top end overhaul. Plan to correct these problems, if necessary.
- Buildup in the cylinders from excessive oil consumption
- Buildup in the cylinders from contamination of the fuel
- Plugging of the aftercooler from coolant that is poorly maintained
- Plugging of the aftercooler from contamination of the inlet air
- Degradation of the oil cooler from hydrogen sulfide in the fuel
Inspect the following components according to the instructions that are in Caterpillar reusability publications. Refer to Guidelines for Reusable Parts and Salvage Operations, SEBF8029, "Index of Publications on Reusability or Salvage of Used Parts".
Your Caterpillar dealer can provide these services and components. Your Caterpillar dealer can ensure that the components are operating within the appropriate specifications.
If you elect to perform an overhaul without the services of a Caterpillar dealer, be aware of the following recommendations.
The following definitions explain the terminology for the services that are performed during an overhaul:
Inspect - Inspect the components according to the instructions that are in Caterpillar reusability publications. Refer to Guidelines for Reusable Parts and Salvage Operations, SEBF8029, "Index of Publications on Reusability or Salvage of Used Parts". The guidelines were developed in order to help Caterpillar dealers and customers to avoid unnecessary expenditures. New parts are not required if the existing parts can still be used, reconditioned, or repaired. If the components are not in the reusability guidelines, refer to the Service Manual, "Specifications" module.
Rebuild - The component can be reconditioned in order to comply with reusability guidelines.
Replace - The service life of the part is exhausted. The part may fail before the next maintenance interval. The part must be replaced with a part that meets functional specifications. The replacement part may be a new part, a CAT remanufactured part, a rebuilt part, or a used part. Some worn components may be exchanged with your Caterpillar dealer. Consult your Caterpillar dealer about repair options for your engine.
Note: The cylinder head may be rebuilt, when possible.
Replace the following components during a top end overhaul.
- Alternator and fan drive belts
- Cylinder heads and gaskets
- Hoses and clamps
- Rod ends for the control linkage of the actuator
- Spark plugs
- Spark plug wires
- Water temperature regulator
Rebuild the following components during a top end overhaul:
- Carburetor
- Gas regulator
- Starting motor
- Turbocharger
- Water pumps
Note: Periodic inspection of the turbocharger is recommended for determining when the turbocharger will require an overhaul. In a few applications, the turbocharger may require rebuilding prior to the top end overhaul. An example is an application with loads that vary frequently. In these cases, rebuilding the turbocharger normally occurs separately from rebuilding the cylinder heads. Some applications can operate longer before the turbocharger requires rebuilding. Only experience can determine the actual need.
Clean the following components. Pressure test the components. Replace the components, if necessary:
- Aftercooler core (if equipped)
- Oil cooler core
Note: It is difficult to clean the aftercooler core when maintenance is not performed.
Note: This procedure may be used for cleaning both the aftercooler core and the oil cooler core.
- Remove the core. For the procedure, refer to the Service Manual, "Disassembly and Assembly" module.
- Turn the core upside-down in order to remove debris.
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NOTICE Do not use a high concentration of caustic cleaner to clean the core. A high concentration of caustic cleaner can attack the internal metals of the core and cause leakage. Only use the recommended concentration of cleaner.
Show/hide tableNOTICE Do not use a high pressure spray for cleaning the fins of the core. A high pressure spray can damage the surface of the fins and reduce the flow of air through the core.
- Back flush the core with cleaner.
Caterpillar recommends the use of Hydrosolv liquid cleaner. Use a two to five percent concentration of the cleaner at temperatures up to
93 °C (200 °F) . Refer to Application Guide, NEHS0526 or consult your Caterpillar dealer for more information. - Steam clean the core in order to remove any residue. Flush the fins of the core. Remove any other trapped debris.
- Wash the core with hot, soapy water. Rinse the core thoroughly with clean water.
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Personal injury can result from air pressure.
Personal injury can result without following proper procedure. When using pressure air, wear a protective face shield and protective clothing.
Maximum air pressure at the nozzle must be less than
205 kPa (30 psi) for cleaning purposes. - Dry the core with compressed air. Direct the air in the reverse direction of the normal flow.
Note: The test pressure for the oil cooler is
790 kPa (115 psi) . The maximum differential pressure of water for the aftercooler is44 kPa (6 psi) . The maximum differential pressure of air for the aftercooler is5.1 kPa (0.74 psi) . - Inspect the core in order to ensure cleanliness. Pressure test the core. Many shops that service radiators are equipped to perform pressure tests. If necessary, repair the core.
- Install the core. For the procedure, refer to the Service Manual, "Disassembly and Assembly" module.
For more information on cleaning the cores, consult your Caterpillar dealer.
Inspect the condition of the exhaust bypass (if equipped). Recondition the component, if necessary. Refer to this Operation and Maintenance Manual, "Exhaust Bypass - Inspect" topic (Maintenance Section).
Inspect the governor for proper operation. Make any repairs that are necessary.
The transformers produce a voltage increase. For good operation, the connections must be clean and secure. Inspect the transformers for the following conditions:
- Dirty insulator
- Loose connections
- Loose connector
- Moisture
Test the resistance of the transformers according to the Service Manual, "Specifications" module. Consult your Caterpillar dealer for assistance.