FAQ for BMW M3 Service Action
I'm with BMW of North America, LLC. Following are answers to some of the questions you've had about the M3 engine service action.
Why are the connecting-rod bearings affected and not the main bearings?
The piston loads produce higher stress and strain on the connecting rod bearings, compared to the stresses imposed on the main bearings. The force produced by the piston is applied directly to the connecting rod bearings whereas it is indirectly applied to the main bearings. As a result, the connecting rod bearings are subject to greater stress and if there is insufficient lubrication, they could experience premature wear.
In addition, the main bearings have a bigger surface area than the connecting rod bearings, which means that the load is better distributed along the surface, so they can resist higher loads. In the M3 engine failure cases we’ve seen, the connecting rod bearings have always failed prior to the main bearings.
Why does the service action only affect the M3 and not the M Roadster / Coupe.
The M3 and the M Roadster and Coupe engines have different torque and power characteristics:
“Red Line” (max. engine speed)
M Roadster/Coupe – 7600 rpm
M3 – 8000 rpm
M Roadster/Coupe – 315 hp
M3 – 333 hp
The M3’s engine is higher revving and produces more power compared to the M Roadster / Coupe. As a result the M3 engine is subject to greater stress and strain. Unfavorable tolerances of the oil pump and extreme driving conditions can lead to insufficient lubrication of the engine which in turn can cause the connecting rod bearings to experience premature wear. The lower powered / revving M Roadster and Coupe engines receive lower stresses on the connecting rod bearings.
If you have any questions, you can reach us at 800-831-1117.
BMW NA Customer Relations