ROD 2137538 - Caterpillar

All D348, D349 And 3400 Series EnginesSUPPLEMENT: 02/14/83SERVICE MAGAZINE, NOVEMBER 29, 1982, PAGE 1.In the article, "Improvements Made To Fuel Ratio Control," change the second sentence, in the third paragraph, under the topic "Description of Change" to read: "The new seal is made of a Viton material and causes less friction between itself and the housing."--------------- END SUPPLEMENT ---------------Reference: Service Magazine, March 15, 1982, Page 8. The article "New Diaphragm Used In Fuel Ratio Control", tells about the use of a new gray silicone diaphragm in the control group.Description of Change: Several improvements have been made to the fuel ratio control groups to increase service life and improve performance (faster reaction time). These improvements include new valve assemblies, a lip-type seal, spring retainer, and an improved diaphragm. Also, a new strainer assembly is used in the governor group on 3406 Truck Engines The two new valve assemblies have smoother bore surfaces for a better fit with the 2P8939 Valve. This smoother surface will improve performance.
A new lip-type seal is used with the new valve assemblies. The new seal is made of a Viton material and causes less friction between itself and the housing. Formerly, two seals were used. These seals have worn the housing in some applications.
The new spring retainer is made from stamped metal. It must be installed with the convex side toward the air chamber. If the new spring retainer is not installed correctly, the fuel ratio control will not work correctly.
An improved diaphragm is now used. This diaphragm now has a rib (bead) around the inside diameter to make a better seal around the retainer assembly. This will prevent leakage of oil into the air chamber. The part number of the diaphragm did not change, but for identification purposes the color was changed to white. The former diaphragm was gray in color.
The new strainer assembly is used in 3406 Truck Engines. The new strainer assembly has a smaller orifice which slows (restricts) the flow of oil to the fuel ratio control. This permits slower action of the fuel ratio control in relation to sudden changes in boost, and more time to change gears without a loss of power. The smaller orifice in the new strainer assembly will not decrease normal acceleration of the engine.
Illustration 1. Location of new parts in fuel ratio control group.Adaptable As: The new parts are direct replacements for the former parts as shown in Chart A. All the parts, except the 2W8449 Strainer, are in effect with the serial numbers shown in Chart B. An in effect serial number for the use of the strainer is not available at this time. It is our recommendation to put an "N" mark on any fuel ratio controls that have had all the new parts installed. This "N" mark will make it easier in the future to tell which fuel ratio controls have the new parts. An "N" mark can also be put on the governor housing when the new strainer is installed. See