TUBE AS 3T6539 - Caterpillar

D398, D399, G379, G398, G399 EnginesAccording to field reports, some of the above model engines have nuts on the main bearing caps which are smaller than standard size (undersize) across the flat sides of the hex. This has no effect on the engine or bearing service life, but can cause problems with tools during engine service work.
To remove the undersize nuts, it will be necessary to use either a 1 11/16" (42.9 mm - 1.69") six-point (single hex) socket, or a 42 mm (1.65") socket.
The tool normally used to remove or install the 3S1356 Nuts is a 1 11/16" (42.9 mm - 1.69") twelve-point (double hex) socket. This socket will not turn the undersize nuts. Also, since this is the size and type of socket used in the 8M9379 Wrench Assembly, it can not be used for access to remove the nuts through the engine inspection covers.
When any of these undersize nuts are found during engine service work, the recommendation is to install new 3S1356 Nuts at assembly.