930113-0600 Tohatsu NUT

Top End Overhaul Information
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 equipmentCaterpillar dealers are equipped with these tools. Cat 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.
Build up in the cylinders from excessive oil consumption
Build up 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
Leaks in the internal coolant passages in water-cooled exhaust manifoldInspect the following components according to the instructions that are in Cat reusability publications. Refer to Guidelines for Reusable Parts and Salvage Operations, SEBF8029, "Index of Publications on Reusability or Salvage of Used Parts".Your Cat 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 Cat dealer, be aware of the following recommendations.Replacing of Components
Replace the following components during a top end overhaul.
Cylinder heads and gaskets
Oil temperature regulators
Water temperature regulatorsRebuilding of Components
Rebuild the following components during a top end overhaul:
Carburetor
Exhaust bypass
Gas regulator
Prelube pump
Starting motor
Turbochargers
Water pumpsNote: 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.Inspecting of Components
Clean the aftercooler core and the oil cooler core. Test the pressure of the components. Replace the components.Note: Cleaning the aftercooler core when proper maintenance is not performed can be difficult. The tank that is opposite of the inlet port and the outlet port cannot be removed for cleaning.Note: This procedure may be used for cleaning both the aftercooler core and the oil cooler core.
Remove the core. For the procedure, see the Service Manual, "Disassembly and Assembly" module. Refer to the "Reference Materials" topic for more information.
Turn the core upside-down to remove debris.
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.
Back flush the core with cleaner.Caterpillar recommends the use of Hydrosolv liquid cleaner. Hydrosolv liquid cleaners are available from your Caterpillar dealer.Use a 2 to 5 percent concentration of the cleaner at temperatures up to 93 °C (200 °F). Refer to Application Guide, NEHS0526 or consult your Cat dealer for more information.
Steam clean the core 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.
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 is 44 kPa (6 psi). The maximum differential pressure of air for the aftercooler is 5.1 kPa (0.74 psi).
Inspect the core to ensure cleanliness. Test the pressure of the core. Many shops that service radiators are equipped to perform pressure tests. If necessary, repair the core.
Install the core. For the procedure, see the Service Manual, "Disassembly and Assembly" module. Refer to the "Reference Materials" topic for more information.For more information on cleaning the cores, consult your Cat dealer.Coupling
For tandem engine arrangements, inspect the coupling for the engines according to the information that is provided by the OEM of the coupling. Check the bolts for proper torque.Governor
Inspect the governor for proper operation. Make any repairs that are necessary.Transformers
Illustration 1 g00850303The transformers produce a voltage increase. For good operation, the connections must be clean and secure. Inspect the transformers for the following conditions:
Damaged connector
Damaged O-rings
Dirty insulator
Loose connections
Loose screws in the top ground spring
MoistureTest the resistance of the transformers according to the Service Manual, "Electronic Troubleshooting" module. Refer to the "Reference Materials" topic for more information. Consult your Cat dealer for assistance.Oil Suction Screen
Hot oil and components can cause personal injury.Do not allow hot oil or components to contact skin.