BMW I6 engines with only 4 main bearings?

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BMW I6 engines with only 4 main bearings?

Occasionally an inline-6 engine will be designed with only 4 main bearings. That is, there is no main bearing between cylinders 1&2, nor between 3&4, nor between 5&6.

I think this was common in some of the older American I6 engines, and maybe some aircraft engines too.

On the page for “Straight-six engine”, Wikipedia indicates that BMW has also done this at some point:

“Many of the more sporty high-performance engines use the four bearing design because of better torsional stiffness (e.g., BMW small straight 6, Ford’s Zephyr 6).”

No further details on the BMW engine(s) is given.

Does anyone know which BMW engine(s) used only 4 main bearings as opposed to the normal 7?

I find the concept of the crankshaft being potentially stiffer in torsion very interesting, and would like to research this further.

Thanks!

Nearly all inline-6 cylinder engines employ 7 main bearings. That is, there is a main bearing between each rod bearing, and one at each end of the crankshaft.Occasionally an inline-6 engine will be designed with only 4 main bearings. That is, there is no main bearing between cylinders 1&2, nor between 3&4, nor between 5&6.I think this was common in some of the older American I6 engines, and maybe some aircraft engines too.On the page for “Straight-six engine”, Wikipedia indicates that BMW has also done this at some point:No further details on the BMW engine(s) is given.Does anyone know which BMW engine(s) used only 4 main bearings as opposed to the normal 7?I find the concept of the crankshaft being potentially stiffer in torsion very interesting, and would like to research this further.Thanks!