• side by side
• Articulated (master and slave)
The side by side means that the opposite cylinder banks are offset by the width of the bottom end bearing. It means a slightly longer engine, with corresponding longer crankpin journals. However access is not restrictive, and spares are the same for both sides.
With the articulated or forked arrangement, the cylinders are diametrically opposite. This gives the shortest possible engine, but access into the crankcase can be awkward, and because the con rods and bearings are different for both banks of cylinders, then this leads to increased costs because of the extra spares required.