0433249 JOHNSON INTAKE MANIFOLD ASSY., Stbd.

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 "PS8965" as the Part Number and "7755" as the Group Number. If administered before failure, use "56" as the Warranty Claim Description Code and use "T" as the SIMS Description Code. If administered after failure, use "96" as the Warranty Claim Description Code and use "Z" as the SIMS Description Code.
Termination Date
August 31, 1997Problem
Some CH55 engines may have the governor torque limiter adjustment set incorrectly from the factory. The incorrect adjustment can result in very little torque rise as the engine is lugged below rated speed of 2100 rpm, and cause customer complaints of "low power" or poor response in the field. The CH35 and CH45 governors have different specifications, and were not affected by the incorrect factory adjustment procedure.
Affected Product
Model & Identification Number
CH55 (7DM1-334, 7DM511-Up7DM560, 7DM563-569, 7DM571-577, 7DM579-581, 7DM589-593 , 7DM595-604, 7DM606-607)
Parts Needed
1 - Dealer Seal and Lockwire for Governor (after adjustment)
1 - 1192940 Gasket-Valve Cover (only if needed)
1 - Dealer Seal and Lockwire for Fuel Setting (only if Static Fuel Setting has been adjusted)
Action Required
READJUST THE GOVERNOR TORQUE LIMITER SETTING:
The governor Torque Limiter setting can be re-adjusted. For this Program, the preferred method of adjustment is done on-machine using a PTO dynamometer and the attached Procedure, " PTO Dynamometer Adjustment of Governor Torque Limiter". This method is the easiest. In this case, it is not necessary to remove the governor from the engine.
- The PTO dynamometer is used to lug the engine so that the Torque Limiter adjustment can be set properly under load. This Program and the Procedure does not include a complete dynamometer test of horsepower.
- If a PTO dynamometer is not available to perform the Torque Limiter adjustment, it will be necessary to remove the governor from the engine, and adjust the Torque Limiter setting on the Governor Calibration Bench. An abbreviated procedure, " Governor Calibration Bench Adjustment of Governor Torque Limiter" for the CH55 governor is attached for the purpose of checking & setting the Torque Limiter only.The Governor Calibration Bench adjustment procedure will take longer, due to time needed to removestall the governor from the engine, and to check the Static Fuel Setting of the engine after the governor has been re-installed on the engine.
- Some machines may have previously had a dealer adjustment of the engine Static Fuel Setting because of a low power complaint.When performing this Program, if machine has a "red" dealer seal on the Static Fuel Setting (under the valve cover), the Static Fuel Setting should be checked, and reset (if needed) to the Static Fuel Setting specification listed on the Engine Information Plate (Label), within 0.10mm.The original factory seals are "yellow".
DISCUSSION - The CH55 Engine Governor is equipped with an externally adjusted "Torque Limiter" to provide a limit on the amount of torque-rise that the governor can provide.The internal torque-cam of the CH55 governor provides extra torque rise (increases dynamic rack) as the engine lugs below the rated speed of 2100 rpm.At 1900 rpm lug (2000 rpm lug on earlier CH55s), theTorque Limiter acts directly on the servo to limit the maximum governor output and prevent any further increase in dynamic rack due to the torque cam.When the governor servo contacts the Torque Limiter screw during lug, no further dynamic rack increase can occur as the engine lugs down, and engine is then limited to its "natural" torque rise.The torque limiter adjustment is originally set during governor calibration at the factory.
The governor Torque Limiter feature is used to assure the engine cannot exceed its operating limits (cylinder pressures & temperatures, exhaust temps, etc) if engine is lugged below 1900 rpm. Excessive torque rise below 1900 rpm could result in overheating and/or engine damage such as head gasket failures or burned valves.
Service Claim Allowances
If PTO dynamometer is not available, and governor is removed for bench test according to the alternate procedure provided, then the labor allowance is:
Parts Disposition
Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.Attach.
Attach.(1-Rework Procedure)Rework Procedure
PTO Dynamometer Adjustment of Governor Torque Limiter
(Preferred Method for This Program)
CH-55 Tractors Only
NOTE 1: If dealer has previously re-adjusted the Static Fuel Setting of the machine due to a "low-power" complaint, the Static Fuel Setting should be checked again, and reset to the Static Fuel Setting specification shown on the Engine Information label within 0.10mm. This should be done before making the Torque Limiter adjustment using the PTO dynamometer procedure shown below.If the original "yellow" factory seal is still in place on the Fuel Setting adjustment under the valve cover, then it is not necessary to check/adjust the Fuel Setting.Do not remove the seal from the Static Fuel Setting unless the setting is incorrect. The Static Fuel Setting can be checked without removing the seal. The seal and lockwire must be removed in order to make an adjustment of the static Fuel Setting.Dealer seals are "red" in color.
NOTE 2: Before beginning this test, dealer must examine the Governor Information Plate, and determine the Governor Group Number (GOV GRP).Adjustment depends upon which part number of governor the engine is equipped with.
1. Set up CH55 Tractor on PTO dynamometer. It will NOT be necessary to measure fuel flow, temperatures, etc for this abbreviated procedure to adjust the Torque Limiter. It is necessary to be able to monitor engine rpm, and to be able to stabilize and hold a full load (lug) condition for several minutes. Use of the 9U7400 Multitach Group (phototach), or equivalent, is recommended to monitor engine rpm while making the adjustment.- Remove governor seal and lockwire
- Remove the small hexagonal-shaped cover-plug on the side of the governor so that the Torque Limiter adjustment