0124641 JOHNSON SCREW

Table 1
Estimated Service Hours Before a Major Overhaul
Fuel Compression Ratio Service Hours
Wellhead gas or natural gas 7.6:1 100000 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 compressionThe 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 compressionNote: 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 soon. 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 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 vibrationAn increase of wear metals in the lube oil indicates that the bearings and the surfaces that wear may require repair. 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 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 a top end overhaul. A major overhaul can also include all the work that is done for an in-frame overhaul. A major overhaul includes more parts and labor. More parts and labor may be required to rebuild the engine. Sometimes, the engine is relocated for disassembly.For the major overhaul, 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.If you elect to perform an overhaul without the services of a Cat 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 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. Consult your Cat dealer about repair options for your engine.
Table 2
Major Overhaul(1)
Procedure Component
Inspect
Replace Camshafts
Connecting rods
Crankshaft
Rebuild Inlet air piping
Replace Aftercooler
Camshaft lifters
Exhaust manifolds
Gear train bearings
Oil cooler
(1) In addition to these procedures, perform the procedures for both the top end overhaul and the in-frame overhaul.