G3500J Engines Caterpillar

Scheduling a Major Overhaul

Generally, a major overhaul is performed for every fifth top end overhaul. The need for a major overhaul is determined by several factors. Some of those factors are the same factors that determine the in-frame overhaul:

• An increase of oil consumption

• An increase of crankcase blowby

• A decrease and variation of cylinder compression

Other factors must be considered for determining a major overhaul:

• Power output

• The service hours of the engine

• Reduced oil pressure

• 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: Oil analysis can 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 generator or 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.

Major Overhaul Information

A major overhaul includes all the work that is done for top end overhauls and in-frame overhauls. A major overhaul includes more parts and labor. More parts and labor are required in to rebuild the engine. Sometimes, the engine is relocated for disassembly.

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.

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 Cat 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 to help Cat 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 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 toward replacement parts. Consult your Cat dealer about repair options for your engine.

If you elect to perform an overhaul without the services of a Cat dealer, be aware of the recommendations in Table 1. Your Cat dealer can provide these services and components.