Undercut crankshaft

By making the crank webs with an offset to them, it is possible to place the main bearings closer together, closely sandwiching the rod passing between them, where this is now a narrower gap than the bearing size.

The overall shape of the crankshaft and its webs is not a problem, but finishing the bearing surfaces by grinding is.

As a result, each bearing must be made and finish-ground individually; then assembled into a built-up crankshaft, usually by shrink-fitting.

One of the few engines to use undercut crankshafts was the Bugatti U-16 aircraft engine,[1] a typical Bugatti approach, where only their unlimited budget and attention to detail could afford such complexities.

The French Ariès narrow-angle V4 of 1907 had a built-up crankshaft with disc webs.