The solution, it would seem, lies on the surface: but is it possible to arrange two rows of cylinders parallel to each other? It will turn out a very compact power unit. But motorbikes with such engines were mass-produced: for example, the legendary Ariel Square Four or the more modern Suzuki RG500 * But here's the subtlety: each row was equipped with its “own” crankshaft. As you might imagine, this was not reflected in the cost of the unit in the best way. Why did the designers use such a cumbersome option?
Let's simulate a diagram: two rows of parallel cylinders working on one crankshaft. In this case, the cylinder axes do not pass through the crankshaft axis - the so-called deaxial displacement of the cylinders occurs. And with it, the forces of lateral friction of the pistons against the walls of the cylinders, already not small, increase many times. At the same time, even modern synthetic oils cannot stop rapid wear - they are forced out of the gap due to the frictional force.
In principle, devices for unloading a piston from lateral forces - crossheads - have long been known. But they so increase the size of the internal combustion engine that they are used only in stationary and marine engines.
And so the idea came up: but shouldn't crossheads be built into the piston? Then it can be reduced to a cylindrical guide sleeve, the piston rests on its inner part of the skirt through the friction ring. Slots are made in the sleeve for the passage of the connecting rod and bosses with a piston pin. The sleeve is attached using a flange clamped with bolts between the flanges of the crankcase and cylinder.