The need for a major overhaul is determined by several factors.
- An increase of oil consumption
- An increase of crankcase blowby
- A decrease and variation of cylinder compression
The following changes in the three conditions normally require a scheduled overhaul:
- A 300 percent increase in oil consumption
- A 200 percent increase in crankcase blowby
- A 20 percent loss of cylinder compression
Note: These indications do not require an engine to be shut down for service. These indications only mean that an engine should be scheduled for service in the near future. If the engine operation is satisfactory, an immediate overhaul is not a requirement.
The engine does not require an overhaul if the engine is operating within acceptable limits for oil consumption, crankcase blowby, and cylinder compression.
Other factors must also be considered for determining a major overhaul:
- 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 need to be serviced. An increase in the levels of noise and vibration indicates that rotating parts require service.
Note: It is possible for oil analysis to 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 Caterpillar 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 of the work that is done for top end overhauls. A major overhaul includes additional parts and labor. Additional parts and labor are required in order to completely rebuild the engine. In some cases, the engine is relocated for disassembly.
For the major overhaul, all of the bearings, seals, gaskets, and components that wear are disassembled. The parts are cleaned and the parts are 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 Caterpillar replacement part.
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 the major overhaul.
- Alternator
- Alternator and fan drive belts
- Camshaft bearings
- Connecting rod bearings
- Crankshaft bearings
- Crankshaft seals
- Crankshaft vibration damper
- Cylinder liners
- Cylinder head and gaskets
- Exhaust manifold
- Gaskets and seals
- Gear train bearings
- Governor
- Hoses and clamps
- Main bearings
- Piston rings
- Rod ends for the control linkage of the actuator
- Spark plugs
- Spark plug wires
- Transformers
- Valve rotators
- Water temperature regulators
- Wiring harnesses
Rebuild the following components during the major overhaul. If the components cannot be rebuilt, replace the components.
- Carburetor
- Cylinder packs
- Exhaust bypass
- Gas regulator
- Inlet air piping
- Oil pump
- Starting motor
- Turbocharger
- Water pumps
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".
- Aftercooler
- Camshafts
- Camshaft followers
- Connecting rods
- Crankshaft
- Gears of the gear train
- Gear train bushings
- Governor
- Inlet air piping
- Oil cooler
- Oil pump
- Pistons
- Transformers