LINKAGE AR 1795144 - Caterpillar

Recession - The valves and the valve seats are worn over time. This causes the valves to recede into the cylinder head. This condition is called “valve recession”.The exhaust valves and valve seats show the greatest wear due to high operating temperatures. The top end overhaul interval is normally scheduled according to exhaust valve recession.The actual measurement of the valve recession inside of the cylinder head is difficult to obtain. Two simpler methods are used to determine valve recession:
Measure the projection of the valve stem above the cylinder head. It is necessary to remove the rocker arms in order to obtain this measurement. This method is more accurate than measuring the projection of the exhaust valve rotators. Measure the projection of the exhaust valve stems with the 4C-2980 Cylinder Head Valve Projection Group.
Measure the projection of the valve rotator above the cylinder head. It is not necessary to remove the rocker arms in order to obtain this measurement. Measure the projection of the exhaust valve rotators with the 148-2997 Valve Recession Tool Group.Make several copies of this Operation and Maintenance Manual, "Valve Data Sheet" (Reference Materials Section). Record the measurements on the sheets.
Measure the projection of the inlet and exhaust valve stems and the exhaust valve rotators at the first 1000 service hours. This measurement is the baseline. The baseline is a reference for subsequent measurements.
Measure the projection of the inlet and exhaust valve rotators when the engine valve lash is checked. Continue this periodic measurement until the projection of the valve rotator has increased by a total of 1.6 mm (.063 inch). This is 70 percent of the maximum limit. Measure the projection of the valve stems when this occurs. This measurement will determine the actual wear of both the valves and the valve seats.
After 70 percent of the maximum limit has been reached, measure the projection of the exhaust valve stems at every 500 hours of operation.
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 valve recession to exceed this limit. The valve head can break. This will cause severe damage in the combustion chamber and the turbocharger.Consult your Caterpillar dealer for assistance.