0318333 JOHNSON COVER, Cylinder head

Table 1
Estimated Service Hours Before a Top End Overhaul
Fuel Compression Ratio Service Hours
Wellhead gas or natural gas 9.2:1 25000
Natural gas 10.5:1 15000
Bio-gas 9.2:1 10000 to 14000 Top end overhauls are normally scheduled according to the projection of exhaust valve stems. This measurement provides an accurate indication of the rate of valve wear. This measurement can be used to predict when a cylinder head requires replacement.Measure the projection of the exhaust valve stems at the first 1000 service hours. This measurement is the baseline. The baseline is a reference for subsequent measurements. Continue to periodically measure the projection.Plan for the top end overhaul as the valve stem projection approaches the maximum limit. Perform the top end overhaul when the valve stem projection has increased by a total of 2.3 mm (.09 inch). Do not allow the projection of the exhaust valve stems to exceed this limit.Note: Generally, cylinder heads wear out at different rates. In some cases, servicing the cylinder heads at different times may be the most economic decision. This depends on the valve stem projection of the individual cylinders. However, this decision must include the costs of additional downtime that is caused by this procedure. Perform an economic analysis in order to determine if cylinder heads should be serviced as a group or divided into smaller groups.Note: The generator or the driven equipment may also require service when the engine overhaul is performed.Top End Overhaul Information
A top end overhaul involves servicing the cylinder heads and turbochargers. Also, some other engine components are inspected.Top end overhauls require more tools than preventive maintenance. The following tools are needed for restoring the engine to factory specifications:
Torque wrenches
Dial indicators
Accurate measurement tools
Cleaning equipment
Rebuilding equipmentCaterpillar dealers are equipped with these tools. Caterpillar dealers can provide a flat rate price for a top end overhaul.Unexpected problems may be found during a top end overhaul. Plan to correct these problems, if necessary.
Buildup in the cylinders from excessive oil consumption
Plugging of the aftercooler from coolant that is poorly maintained
Degradation of the oil cooler from hydrogen sulfide in the fuelInspect 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".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.
Table 2
Top End Overhaul
Procedure Component
Inspect/Replace Seals for the gas admission valve
Precombustion chambers
Drive coupling
Rebuild Gas pressure regulator
Starting motor
Turbochargers
Replace Connecting rod bearings
Cylinder heads and gaskets
Oil temperature regulators
Spark plug extenders
Water temperature regulators