BOOM & BEARING AS 4592842 - Caterpillar

--------------- END SUPPLEMENT ---------------SUPPLEMENT: 08/00/91Engine News; May 1991; Page 9; "Rear Gear (Cam Drive) Groups t Improved" for 3500 Family Of Engines.In Chart A under the column titled "Model", put a mark through 776B and 777B. The changes to the carburized gears did not take effect on these two models until the serial numbers listed in Chart B. Also, in Chart B, add the serial number "67Z829" for 3512 Generator Set (Slow Speed).
--------------- END SUPPLEMENT ---------------SUPPLEMENT: 07/00/91Engine News; May 1991; Page 9; "Rear Gear (Cam Drive) Groups Improved" for 3500 Family Of Engines.In the Adapt To:section, add the following Note.
The new gears and gear assemblies when used together, along with the other new parts, including the cylinder block modification, are replacements for the former gears and gear assemblies. DO NOT MIX the new shafts, bearings, or gear assemblies with the former shafts, bearings, or other gear assemblies. Since the new shafts are slightly larger in diameter than the former shafts, a former gear assembly bearing used on a new shaft may not have enough clearance for adequate oil film thickness. The former bearings, thrust plates, washers, bolts, etc., are still available for parts service if the gears or shafts are not changed.--------------- END SUPPLEMENT ---------------Description of Change: Several changes have been made to the 3500 Family Of Engines which will improve the service life and reliability of the rear gear groups. These improvements include: - New cam drive gears, idler gears, and cluster gears now have a deeper case depth of hardened material (carburized).- The sleeve bearings in the cluster gears and idler gears have been changed from steel-backed aluminum bearings to steel-backed bronze bearings. This will increase the bearings fatigue resistance.- The cluster and idler gear shafts are slightly larger in diameter. This reduces the clearance between the shaft and the sleeve bearings to minimize gear wobble.- New cluster and idler gear shafts have two smaller oil supply holes instead of just one large diameter hole. This will provide better distribution of the oil to the bearing.- Idler gear shafts have a thicker flange to prevent breakage at the corners of the half flange.- The bolts that secure the idler gear shafts to the cylinder block have been changed from 1/2 to 5/8 inch diameter. Also, the torque has been increased from 135 15 N m (100 10 lb ft) to 240 20 N m (180 15 lb ft). This will help keep the bolts from working loose.- The cylinder block and idler gear thrust washers have been changed to accept the larger bolts.Adaptable To: See Chart A for the effectivity for the carburized gears used in the low speed engines. See Chart B for the effectivity for the remaining improvements (including the carburized gears). Illustration 1 shows a typical rear gear (cam drive) group. The item numbers listed in the illustration are shown in Charts C through G. These charts show the new and former part numbers and descriptions for the