Two-stroke engines are nowadays, actually only found in small motorcycles and in the really big Diesel engines. In the four-wheel sector, for well known reasons, nothing is offered. Going back more than fifty years, it was a different story. The above shown V4-engine with charging pump is an example of what was found in the upper-class cars at that time.
At first glance, one could mistake it for a V6-engine. Having a closer look at picture 1, it can be seen that the two lower pistons are different from the other four. These two pistons
function as a charging pump. They are sealed against the oil sump through small pistons and with each stroke they build up pressure for the other cylinders, alternatively from the top side and then again from the underside. The other cylinders work on the, at that time, common principle of cross-flow scavenging.
The pre-compression in the crankcase is taken over by the charging pump. This is why the pistons have oil rings and a crankcase like those found in four-stroke engines. However, the con-rod and crankshaft have needle-bearings and are not lubricated by the oil circulation but by splash lubrication like in a manual gearbox. The oil is taken up by small tongues on the con-rods dipping into the oil bath providing a droplet shaped oil-mist.
The engine was developed from approx. 1927 onwards and was conceived for the somewhat larger front-wheel drive models. Indeed, even the, in 1929 planned serial introduction, could not be adhered to. When it finally went into production it really proved to be a problem-child, in addition, it also did not achieve the planned advantage of having a lower fuel consumption.
It was not yet adapted for the Schnürle-loop scavenging found in other models and was also pretty much infested with bugs as well. Damages to the, pretty expensive crankshaft, piston-seizure and overheating led to a great deal of customer dissatisfaction, despite the fact that the series was small. Naturally, this didn't get any better with the stronger 1000- and 1100cc versions.
It is said, that the customer service even provided individual house visits, unimaginable nowadays. Only after a, much cheaper to produce three cylinder in-line engine appeared, were the problems solved. It would appear, that the charging and the larger cylinders in two-strokes, could simply not be bundled up into an efficient machine. 11/11