| Message: | | This reponse to my engine failure thread on the bmwm5.com board was just posted. I had asked this individual whether he had experienced a failure or whether he worked for BMW.
"I work at a BMW/MB/Porsche service/tuner shop in Beverly Hills, a few minutes away from Beverly Hills BMW. I've got a few friends at the dealer and inside BMWNA, who seem to have cited the problem as a defective rod bearing, usually cylinder #3. The E36 Euro M3s (S52 double vanos 3.2L => 321HP version), were rumored to also have rod bearing problems. The problem has to do with the tremendous inertial stresses the crank/rods are exposed to. As a comparison, the Acura NSX 3.2L V6 (8000 RPM redline) has bore/stroke dimensions of 93mm/78mm...shaped more like a short stroke F1 engine to allow for high rpms, while minimizing intertial forces at the upper revband. However, the consequence of over-square engine dimensions is less low-end and overall torque. An F1 car does not have to worry about low-end torque as it only weighs about 1200 lbs. This is why the NSX was designed with an all-aluminum composite chassis/body in order to conserve weight and still allow for great acceleration. The engineers at ///M are faced with a different task. The M3 is targeted towards a different market segment, very different from the NSX. The NSX tips the scales at 2900lbs, the M3 3400lbs. Hence, an over-square engine design will not suffice and consequently the M3's S54 has a slightly under-square engine with a bore of 87mm and a lengthy stroke of 91mm. The advantage is a powerful, flat torque curve as illustrated by the M3's 262ft.lbs vs. the NSX's 224ft.lbs (out of the same displacement). However, the trade-off is tremendous inertial stress on the bottom-end above 7000 RPMs. It really is no big surprise then, why the M3's are blowing engines...the high redline mixed with a long stroke will garner some amount of engine failure, but considering the amount of failures vs. total production, BMW is actually in good shape. However, I can pretty much guarantee you that the next M3 will have a smaller displacement V8, most lilkely a tuned variant of the new N62 Valvetronic 4.4L V8 currently found in the 745i".
Many thanks to the above for helping us understand more about what may be happening. In an engine as highly stressed as the E46 M3's, it's easy to see how one component that is supplied to BMW that might be even slightly out of 'spec' can cause tremendous problems, i.e. catastrophic engine failure.
thebishman
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