- An increase of oil consumption
- An increase of crankcase blowby
- A decrease and variation of cylinder compression
Other factors must also be considered for determining a major overhaul:
- 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 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.
For the major overhaul, all of the bearings, seals, gaskets, and components that wear are disassembled. The parts are cleaned. 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.
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 is 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 for a credit on replacement parts. Consult your Caterpillar dealer about repair options for your engine.
If you elect to perform an overhaul without the services of a Caterpillar dealer, be aware of the recommendations in Table 1.
| Recommendations for the Major Overhaul | |
|---|---|
| Service | Component |
| Rebuild | Centrifugal oil filters |
| Cylinder heads | |
| Starting motor | |
| Vibration damper | |
| Replace | Accessory group bearings |
| Camshaft bearings (1) | |
| Connecting rod bearings (2) | |
| Cylinder head valves and valve guides | |
| Cylinder head valve spring guides | |
| Exhaust manifold bellows | |
| Exhaust shields | |
| Front gear train bearings (3) | |
| Fuel injectors | |
| Main bearings (2) | |
| Oil pump bearings | |
| Oil temperature regulators | |
| Turbocharger bearings and bushings | |
| Water pump bearings | |
| Water temperature regulators | |
| Inspect | Aftercooler cores |
| Alarm and shutoff controls | |
| Camshafts (1) (4) | |
| Crankshaft (2) (4) | |
| Cylinder block | |
| Cylinder liners | |
| Cylinder sleeves | |
| Exhaust manifolds | |
| Front gear group (3) | |
| Oil cooler | |
| Oil pump bushings | |
| Oil suction screen | |
| Pistons and piston rings | |
| Priority valve | |
| Rear gear group (3) | |
| Rear gear train bearings (3) | |
| Rocker arm bearings | |
| Thermocouples | |
| Thrust bearings | |
| Valve mechanism group | |
| Replace the gaskets and seals of these components. | Air inlet lines |
| Camshaft front covers | |
| Camshaft drive gear covers | |
| Central structure covers | |
| Crankcase side covers | |
| Crankshaft (5) | |
| Crankshaft vibration damper | |
| Cylinder heads | |
| Exhaust manifold | |
| Front housing group | |
| Fuel lines | |
| Fuel transfer pump | |
| Gear inspection group | |
| Oil cooler | |
| Oil lines | |
| Oil temperature regulators | |
| O-ring seals and plugs | |
| Power take-off covers | |
| Priority valve group | |
| Rear gear train | |
| Rear housing group | |
| Rear structure covers | |
| Turbocharger | |
| Valve covers | |
| Water lines | |
| Water pumps | |
| Water temperature regulators | |
| ( 1 ) | Inspect the camshaft for damage to the journals and the lobes. Inspect the camshaft bearings and the camshaft followers for signs of wear and/or scuffing. |
| ( 2 ) | Inspect the crankshaft for these conditions: deflection, damage to the journals and bearing material that has seized to the journals. Inspect the profile and the taper of the crankshaft journals. Compare the crankshaft journals to the wear patterns in the connecting rod bearings and the main bearings. |
| ( 3 ) | Inspect the gears and the bushings of the gear trains for worn gear teeth, unusual fit, and unusual wear. |
| ( 4 ) | If the crankshaft or the camshaft are removed for any reason, use the magnetic particle inspection process to check for cracks. |
| ( 5 ) | Inspect the area around the front seal and the rear seal of the crankshaft. It is not necessary to replace a crankshaft seal if the seal is not leaking. |