WINDOW AS-CAB 2584093 - Caterpillar

Valve 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 scheduled according to the recession of the exhaust valves. However, measuring the actual valve recession in the cylinder head is difficult. A simpler method is used to determine the valve recession:
Measure the projection of the valve stem above the cylinder head.Measure the projection of the exhaust valve stem for G3500C and G3500E engines with a 502-1422 Tool As.Record the measurements on the Operation and Maintenance Manual, "Valve Data Sheet" (Reference Materials Section).
Measure the projection of the exhaust valve stem after 250 service hours. This measurement is the baseline. The baseline is a reference for subsequent measurements.
Measure the projection of the exhaust valve stem at the first 1000 service hours.
Illustration 1 shows schedules for determining subsequent intervals. Determine the increase in the valve stem projection from 250 service hours to 1000 service hours. After determining the increase, find the schedule that best fits the measured increase in the valve stem projection.
After 70 percent of the maximum limit has been reached, measure the projection of the exhaust valve stem at every 1000 hours of operation. The 70 percent is 1.60 mm (0.063 inch).
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. This condition 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.
Illustration 1 g01115573
(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, the "Valve Data Sheet" (reference section) shows that the increase in the valve stem projection at the initial 1000 service hour measurement shows a valve recession of 0.152 mm (0.0060 inch). This measurement would allow you to use Schedule (C). According to Schedule (C), the next interval for measuring that cylinder is at 5000 service hours. Another cylinder may have a valve recession of 0.254 mm (0.0100 inch). According to Schedule (A), the next interval for measuring that cylinder is at 3000 service hours.When different cylinders require different schedules, the schedule that requires the most frequent measurements should be used for all cylinders. Subsequent measurements can result in changing the schedule that is used. For example, if the first measurement indicates that Schedule (A) should be used, the next measurement