BMW 330xi Drive train thumping / banging in turns

Vehicle Details: 2006 BMW 330xi.  121000 miles

Technician: Todd

Client Concern:

Client noticed thumping or banging noise when in sharper turns like when navigating a driveway.  Also noticeable but not as pronounced when doing faster turns at speed (merging off a freeway).

Diagnostic Process:

Initially the client took his car back to his tire shop since this problem seemed to occur shortly after having tires replaced.  The tire shop could find nothing wrong with the basic suspension and drive train components (eg:  ball joints, axles and CV joints, struts, etc) and thus they advising seeing a BMW specialist.

Upon arrival Todd performed the same inspection as the tire shop but when that proved to be fruitless he checked the engine mounts – knowing the pattern failure of engine mount to cylinder block bolts.  Sure enough the bolts were broken (engine mount bracket removed in this picture):

BMW N52 engine - broken engine mount bolts

BMW N52 engine – broken engine mount bolts

Repair Process:

The repair requires extraction of the bolts and replacing them with new.

N52 engine mount bolts

N52 engine mount bolts

N52 right side engine mount bracket

N52 right side engine mount bracket

Once re-secured the vehicle is test drive to ensure the client’s concern has been resolved.  We have NOT seen this escalate into bigger problems yet but we suspect that driving one of these cars with a broken / detached engine mount will eventually cause other problems.

 

Technical Discussion:

The reason BMW use this fastener (bolt) style is the N52 engine has a magnesium block.  A steel fastener, in this application, would cease in the block thus aluminum fasteners are employed.  Unfortunately they aren’t as strong as steel and can break.  On a positive note we have only seen this problem with the all-wheel-drive (xi) vehicles / we suspect this is due to additional rotational forces from the front axles.