PULLEY-FAN DRIVE 9N0337 - Caterpillar

Caterpillar: Confidential Yellow
The information supplied in this service letter may not be valid after the termination date of this program. Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.
This Program can be administered either before or after a failure. In either case the decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS4612" as Part Number, "7755" as Group Number, and "96" as Description Code.
Although this program can be administered either before or after failure (exhaust valve sticking), it is recommended that it be implemented before failure only in northern or high altitude climates that regularly have winter temperatures of -10°C (15°F) or lower. Do all applicable portions of this Service Letter.
Termination Date
August 31, 1992Problem
Exhaust valve sticking may occur at start up on 1991 model year 3116 Truck Engines rated 215 and 250 hp operating in areas with cold ambient temperatures. Engines rated 170 and 185 hp that have serial numbers beginning with "2BK" are NOT considered to be at risk, and are NOT ELIGIBLE for this update.
Removing four exhaust valve stem seal assemblies (cylinders 2, 3, 4, and 5) reduces the risk of valve sticking while still meeting emissions requirements. Installing a new coolant temperature switch and control module for the air inlet heater, will allow the heater to run up to 20 minutes in cold weather and improve combustion during cold starts. Increasing the engine speed to 1000-1200 rpm after starting in cold weather will decrease engine warm-up time.
Affected Product
Three groups of engines are affected:
Group 1 - Engines built WITH exhaust valve stem seal assemblies installed ON ALL CYLINDERS.Group 2 - Engines built WITHOUT exhaust valve stem seal assemblies ON CYLINDERS 3 AND 4.Group 3 - Engines which already have the exhaust valve stem seal assembly changes and new coolant temperature switch. This group of engines needs ONLY the new control module.Serial number ranges for these three groups overlap due to factory rework.
A complete serial number list is shown below for each group.
The intent of this Service Letter is the same for Group 1 and Group 2 engines (exhaust valve seal changes, coolant temperature switch, and control module). The only difference is that Group 1 engines need 4 exhaust valve stem seal assemblies removed, and Group 2 engines need only 2 additional exhaust valve stem seal assemblies removed. Group 3 engines need ONLY the new control module because the valve seal changes and coolant temperature switch were added at the factory. The table below summarizes the changes being made.
This program affects all 1991 and 1991-I model vehicles with 1991 model year 3116 Truck Engines rated 215 and 250 hp that have serial numbers beginning with "2BK" (1991 emissions).
A separate Service Letter, PS4568, dated March 19, 1991, has been issued to address a similar problem on 1990 model year truck engines that have serial numbers beginning with "7SF" (1990 emissions) in 1990 and 1991 model year