GEAR (29 Teeth) 1P1610 - Caterpillar

Valve Recession - The valves and the valve seats are worn over time. Wearing 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 is normally scheduled according to the exhaust valve recession.It is difficult to obtain an accurate measurement of valve recession inside the cylinder head. Use the following method in order to determine the valve recession:
Remove the valve cover. For instructions, see the Service Manual, "Disassembly and Assembly" module.
Move the rocker arm from the top of the valve stem.
Use a depth micrometer. Obtain the measurement from the tip of the valve stem to the cylinder head. Obtain this measurement for each exhaust valve. Make several copies of this Operation and Maintenance Manual, "Valve Data Sheet" (Reference Materials Section). Record the measurements on the sheets.
The projection of the exhaust valve stems should be measured after completion of the initial start-up tests and the engine commissioning. This measurement is the baseline. The baseline is a reference for subsequent measurements.
Measure the projection of the exhaust valve rotators at the first oil change interval. Illustration 1 shows schedules for determining subsequent intervals.
Illustration 1 g00320513
(A) Schedule
(B) Schedule
(C) Schedule
(Y) Valve recession in millimeters (inches)
(X) Hours of operation
(1) 0.254 mm (0.0100 inch)
(2) 0.218 mm (0.0086 inch)
(3) 0.152 mm (0.0060 inch) To determine intervals, use the point on the graph in Illustration 1 that is closest to the measurement for each cylinder.For example, suppose that the measurement that was obtained at the initial oil change shows a valve recession of approximately 0.152 mm (0.0060 inch). According to Schedule (C), the next interval for measuring that cylinder is at 5000 service hours. Another cylinder may have a valve recession of approximately 0.254 mm (0.0100 inch). According to Schedule (A), the next interval for measuring that cylinder is at 3000 service hours.
After 70 percent of the maximum limit has been reached, measure the projection of the exhaust valve stems at every 750 hours of operation (turbocharged engines).
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 (0.09 inch). Do not allow the valve recession to exceed this limit. The valve head can break. Breaking of the valve head will cause severe damage in the combustion chamber and the turbocharger.Consult your Cat dealer for assistance.