CYLINDER GP-AIR/HYDRAULIC 8W3405 - Caterpillar

Recession - The valves and the valve seats are worn over time. This wear causes the valves to recede into the cylinder head. This condition is called “valve recession”.The top end overhaul is typically scheduled according to the amount of valve recession. The amount of valve recession should be monitored on both intake and exhaust valves. However, measuring the actual valve recession in the cylinder head is difficult. A simpler method is used to determine the valve recession:
Valve stem projection is measured above the cylinder head.Measure the projection of the exhaust valve stems with a 502-1422 Valve Recession Tool Group. Follow the instructions that are provided with the tool group.Record the measurements on the Operation and Maintenance Manual, "Valve Data Sheet" (Reference Materials Section).
Measure the projection of the exhaust valve stems after 250 service hours. This measurement is the baseline. The baseline is a reference for subsequent measurements.
Plan for the top end overhaul as the projection of the valve stem approaches the maximum limit. Perform the top end overhaul when the projection of the valve stem has increased by a total of 2.3 mm (0.09 inch). Do not allow the recession of the exhaust valves to exceed this limit. The valve head can break which will cause severe damage in the combustion chamber.
Check the measurement for a difference in the valve recession that is greater than 1 mm (0.039 inch) for the valves that share a valve bridge. If this measurement is exceeded for two successive measurements, replacement of the cylinder head is necessary.