10/28/2009
Click on a thumbnail to see the full-size image
BMW Head Bolt Threads Pulling Out of Block During Engine Reassembly
Affects all BMW models equipped with M52TU and M54 engines
While performing the torque procedure on the cylinder head during engine reassembly, the head bolt
threads strip out of the block on some BMW M52TU and M54 engines. Typically, this occurs during the repair of an engine that has been overheated.
The cause of the problem is due to an overheat condition that has weakened the structure of the aluminum block assembly in the area of the bolt threads.
In cases where an M54 engine needs to be disassembled due to an overheating event, the following steps should be taken:
Before removing the cylinder head, loosen and re-torque each head bolt to ensure thread strength and integrity.
If all head bolts achieve correct torque, proceed with cylinder head removal. Once removed, use a straight edge on the block surface, as well as the cylinder head, to determine any deviation caused by the overheat. Be especially aware of any protrusion of the cylinder liners above the surface of the block.
If a head bolt strips during the re-torque, BMW recommends replacing the engine/block.
Some or all of the technical information was provided by the
Automotive Parts Remanufacturers Association (APRA). For more
information on technical bulletins available through APRA call
703-968-2772 or visit www.AutoBulletins.com.