The need for a major overhaul is determined by several factors.
- An increase of oil consumption
- An increase of crankcase blowby
- The total amount of fuel consumption
- The service hours of the engine
- The wear metal analysis of the lube oil
- An increase in the levels of noise and vibration
An increase of wear metals in the lube oil indicates that the bearings and the surfaces that wear may require service. An increase in the levels of noise and vibration indicates that rotating parts require service.
Note: Oil analysis may indicate a decrease of wear metals in the lube oil. The cylinder liners may be worn so that polishing of the bore occurs. Also, the increased use of lube oil will dilute the wear metals.
Monitor the engine as the engine accumulates service hours. Consult your Cat dealer about scheduling a major overhaul.
Note: The driven equipment may also require service when the engine is overhauled. Refer to the literature that is provided by the OEM of the driven equipment.
A major overhaul includes all the work that is done for the top end overhaul. A major overhaul includes more parts and labor. More parts and labor are required to rebuild the engine.
For the major overhaul, all the bearings, seals, gaskets, and components that wear are disassembled. The parts are cleaned and inspected. If necessary, the parts are replaced. The crankshaft is measured for wear. The crankshaft may require regrinding. Alternatively, the crankshaft may be replaced with a Cat replacement part.
Your Cat dealer can provide these services and components. Your Cat dealer can ensure that the components are operating within the appropriate specifications.
Replace the following components during the major overhaul:
- Aftercooler core
- Aftertreatment air regulator
- Aftertreatment air strainer
- Aftertreatment catalysts
- Aftertreatment DEF nozzle
- Aftertreatment DEF pump
- Aftertreatment DEF strainer
- Aftertreatment electrical harness
- Aftertreatment sensors (temperature, level, and pressure)
- Aftertreatment solenoid valve
- Camshaft bearings
- Camshaft thrust washer
- Connecting rod bearings
- Crankshaft seals
- Crankshaft thrust washers
- Crankshaft vibration damper bolts
- Engine sensors (temperature, level, speed, and pressure)
- Engine speed sensors
- Engine wiring harness
- Exhaust manifold bellows, clamps, bolts
- Exhaust manifold seals
- Flex pipe bellows and clamps
- Flex pipe bellows heat shields
- Flywheel bolts
- Fuel injectors
- Fuel transfer pump
- Gear train bearings and bushings
- High-pressure fuel lines
- High-pressure fuel pump
- Inlet manifold gaskets and seals
- Main bearings
- Oil cooler core
- Piston rings
- Turbocharger
Inspection, Reconditioning, or Exchanging of Components
Inspect 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".
Recondition the worn components or exchange the components, if necessary. Your Cat dealer can provide these services and components.
- Aftertreatment CEM structure
- Camshaft followers
- Connecting rods
- Coolant temperature regulator(Jacket Water)
- Crankshaft
- Crankshaft vibration damper
- Cylinder head assembly
- Cylinder liners
- Fuel pressure regulating valve inspect
- Oil cooler bypass valve
- Oil pressure regulating valve
- Oil pump
- Jacket water pump
- Pistons
- Piston pins
- Prelube pump
- SCAC water pump
- Rocker arms
- Rocker shafts
- Starting motors
Inspect 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".
- Camshaft
- Driven equipment (alignment)
- Engine control module
- Engine cylinder block
- Engine heat shielding
- Exhaust manifold
- Exhaust bellows shields
- Turbine outlet elbows
- Flexible pipe heat shielding
- Flywheel
- Flywheel ring gear
- Gear train front
- Gear train rear
- Front gear train (gears)
- Inlet manifold
- Rear gear train
- Software
Inspect the camshaft for damage to the journals and the lobes.
Inspect the crankshaft for any of the following conditions:
- Deflection
- Damage to the journals
- Bearing material that has seized to the journals
Check the journal taper and the profile of the crankshaft journals. Check these components by interpreting the wear patterns on the following components:
- Rod bearing
- Main bearings
Note: If the crankshaft or the camshaft are removed for any reason, use the magnetic particle inspection process to check for cracks.
Replace the crankshaft vibration damper if any of the following conditions occur:
- Engine failure due to a broken crankshaft
- Excessive wear of the front bearing for the crankshaft
- Excessive wear of the gear train that is not caused by a lack of lubrication
Inspect the gears of the gear train and inspect the gear train bushings for the following conditions:
- Worn gear teeth
- Unusual fit
- Unusual wear
In addition to the inspection of components, inspect the alignment of the driven equipment. See the Application and Installation Guide for the engine or see the literature that is provided by the OEM of the driven equipment.
Clean the oil cooler core and the aftercooler core. Then, pressure test both of these cores. For instructions on cleaning the cores, see this Operation and Maintenance Manual, "Aftercooler Core - Inspect/Clean" topic.
Clean the oil suction screen. Also, remove side covers to clean the oil sump. For instructions on removal and installation of components, see the Service Manual, "Disassembly and Assembly" module.
For conventional heavy-duty antifreeze/coolant, check the concentration of supplemental coolant additive (SCA) regularly. The concentration of SCA can be checked with an S·O·S coolant analysis (Level 1). A more detailed coolant analysis is recommended periodically.
For example, considerable deposits are found in the water jacket areas on the external cooling system, but the concentrations of coolant additives were carefully maintained. The coolant water probably contained minerals which were deposited on the engine over time.
A coolant analysis can be conducted to verify the condition of the water that is being used in the cooling system. A full water analysis may be obtained from the following sources:
- Cat dealer
- Local water utility company
- Agricultural agent
- Independent laboratory
Caterpillar recommends an S·O·S coolant analysis (Level II) which is a comprehensive chemical evaluation of the coolant. This analysis is also a check of the overall condition inside the cooling system. The following services are provided:
- Full Level 1 analysis
- Identification of the source of metal corrosion and of contaminants
- Identification of buildup of the impurities that cause corrosion
- Identification of buildup of the impurities that cause scaling
- Determination of possible electrolysis within the engine cooling system
A report of the results of the analysis is provided. Maintenance recommendations are based on the results.
For more information about S·O·S coolant analysis, consult your Cat dealer.