CONNECTOR AS 1488338 - Caterpillar

3408 Industrial, Marine, Generator Set, and Truck Engines;
631D, 633D, 637D, 637D (PP),
639D, 768C Tractors;
769C TrucksSUPPLEMENT: 05/26/86SERVICE MAGAZINE, AUGUST 15, 1983, PAGE 14, "Troubleshooting Engine Vibration; Damper Adapter Can Be Changed".In the Adapter Replacement Chart, the 2W2618 Adapter and the 4N2109 Adapter were referenced by a footnote describing the adapters as having nine bolt holes. Both of these adapters have six mounting bolt holes. Change the Footnote 1 for both of these adapters to a Footnote 3, "These adapters have six mounting bolt holes". In the topic "Modification", change the first sentence to read, "For engines equipped with a damper adapter that has either nine bolt holes or six mounting bolt holes, install a new adapter as shown on the chart".
--------------- END SUPPLEMENT ---------------According to field reports, some customers have had problems with too much vibration in the front end of the engine. Most of these problems have been on engines which have a heavy component (like a large pulley or sprocket) installed on the front of the crankshaft. An analysis shows that this addition of weight can increase the effect of small differences in crankshaft balance, which are normally within (inside) tolerance specifications. The result is too much vibration during operation at normal engine rpm.
In addition to the effect of a heavy weight on crankshaft balance, several other factors can cause engine vibration: ... Any out-of-balance equipment or attachments installed on the crankshaft.... Wrong alignment of equipment driven from the crankshaft.... The relation between the vibration frequencies of the engine and the engine mountings.
Engine vibration caused by any of these three factors (out-of-balance equipment, wrong alignment of equipment, or the engine mountings) can be corrected at the source. Vibration caused by a heavy weight installed on the front of the crankshaft can be corrected by a modification of the damper adapter or the installation of a new adapter. See the chart and the topic "Modification". To find which of the different factors is the source of the vibration, it will be necessary to make an analysis of the problem. A Special Instruction, Form SEHS7914, "Troubleshooting Engine Vibration In Vehicular Equipment" is available, which gives methods and procedures to use for vibration analysis, and can be used as a reference.
MODIFICATION: For engines equipped with a damper adapter that has nine bolt holes, install a new adapter as shown in the chart. For engines equipped with a 6N7787 Adapter (which has twelve bolt holes), make a modification as follows: 1. Turn the engine crankshaft until the piston of number one cylinder is at the top dead center (TDC) position. See the topic "Finding Top Center Compression Position For Number One Piston" in the Service Manual.2. Remove any accessories or equipment (pulleys, sprockets, etc.) fastened to the 6N7787 Adapter.3. Remove the four 2D8426 Studs from the holes shown in the illustration. Be sure to remove the correct studs, as seen from the front of the engine.4. Install four 2D8155 Studs in these four holes only, and tighten to a torque of