Information on Longer Main Bearing Cap Bolts Required on Certain 2001-2006 LB7, LLY, LBZ Duramax Diesel Engines

1. Second Design
2. First Design

This bulletin is being published to aid technicians in how to identify the Mid-Year change to the Main Bearing Bolt Lengths. During the early production of 2006 Duramax™ diesel engines, a design change was made to the bearing cap bolt and bore for increased robustness. This change includes a 4 mm (0.15 in) longer main bearing cap bolt along with a deeper tapped hole and a deeper counter bore. The new bolt can be identified by a raised circle formed into the bolt head as shown in the above illustration.

Notice: Use of the incorrect bolt will result in engine damage. The shorter bolt will not have enough thread engagement in the newer blocks due to the deeper counter bore, and the longer bolts will bottom out in the older blocks before achieving the proper clamp load. Measurement of the bolt length is not a reliable method of identifying the bolt, as the bolts will stretch to a varying degree after installation. The main bearing cap bolts should not be reused in service.

When performing service work on ANY model year Duramax™ engine, the main bearing cap bolts must be replaced with the same type of bolt that was originally installed. Use the raised circle identifying mark on the bolt head to determine which bolt to use.

It is possible that a prior year vehicle (2001+) could have the newer block with a deeper counter bore if it had an engine replacement after the block change was implemented in production. This is possible because some long block service engines may be built with new production components, such as engine blocks.

In the event that the raised circle identifying mark on the bolt head cannot be relied upon to determine the correct bolt usage, the engine block production date/time stamp may be used.

The above engine block graphic illustration shows the location of the block’s production date/time stamp behind the oil cooler. This date and time indicates the beginning of usage for the longer main bearing cap bolt. Any block built before this time will require the shorter bolt. The production date and time can be determined as follows:

Parts are expected to be available from GMSPO on January 25, 2006.