SEAL 3956815 - 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 can be difficult. A simpler method is used to determine the valve recession:
Measure the projection of the valve rotator above the cylinder head.Measure the projection of the exhaust valve rotators with a 334-7085 Valve Recession Tool. Follow the instructions that are provided with the tool.Record the measurements on the Operation and Maintenance Manual, "Valve Data Sheet" (Reference Materials Section).
Measure the projection of the exhaust valve rotators after 250 service hours. This measurement is the baseline. The baseline is a reference for subsequent measurements.
Measure the projection of the exhaust valve rotators at the first 1000 service hours.
Plan for the top end overhaul as the projection of the valve rotator approaches the maximum limit. Perform the top end overhaul when the projection of the valve rotator 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. This break will cause severe damage in the combustion chamber.
Check the measurement data 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.