KrAZ 214 Truck: The Curious Engineering of a Two-Stroke Diesel Engine

May 22, 2023, 9:52 p.m
PiataAuto.md editors

Last week, we published a short article with video, in which a KrAZ 214 truck was making its way through Germany, still being operated there, and several readers suggested we talk more about its engineering, which was truly a curious one. Especially since this truck had a two-stroke diesel engine, and often when we talk about such engines, a lot of comments appear, asking if I was wrong and how there can be, in general, two-stroke diesel engines.

But the truth is that there are two-stroke diesels and there were a lot of them in history, installed both on trucks and on locomotives or even ships, and ships still keep such engines today. In just the last few months I’ve written about various vehicles or two-stroke diesel engines — the British truck Commer TS3the American truck Peterbilt 352 Pacemakerthe German truck Krupp Titanthe military truck Oshkosh HEMTTabout the 2-stroke triangular diesel engine Napier Delticabout the most powerful marine diesel engine from the world, about the largest container ship from the world, about a Alfa Romeo van with the same engine time and even about the oldest locomotive in Moldova. All these vehicles have two-stroke diesel engines and, disregarding the emissions generated by them, they gave good combustion efficiency, which is precisely why they have been preserved for so long.

Well, now we return to the KrAZ 214 truck, once produced at the Kremencuk factory, on the territory of today’s Ukraine. KrAZ trucks were designed to be the largest and most powerful of those allowed on public roads, therefore this truck was launched in 1956 with a remarkable ability to tow 50 tons behind it. A year later, the truck was also launched Tatra T141which could tow 100 tons behind it, but for 1956 and the region it was launched in, the KrAZ 214 was an impressively engineered truck.

The truck was created from the start with a 6×6 formula, to be able to have enough grip to tow such heavy weights. There was a torque reducer, which made it possible to transmit a very low torque ratio, and the differentials were mechanically lockable. The front power could be disconnected for road trips, but the maximum speed was not high — 55 km/h.

The truck had a 5-speed gearbox, manual of course. The truck weighed 12.4 tons and had a payload of 7 tons.

The engine, however, is the most interesting part here. It was not created at the factory in Kremenchuk, and that’s because, in fact, for the first three years, the truck was assembled at the engine factory in Yarolav, only then moving to Kremenchuk. The engine was a diesel, two-stroke, as I said, and had a cylinder capacity of 6.97 liters, with the code name given by the factory in Yaroslav — YaAZ-M206B. But that is not his primary source either.

The engine had 6 cylinders in line and developed 205-206 HP. The engineering of this engine was, however, practically identical to that of the American GMC 6-71 engine, where the index 6 meant 6 cylinders, and 71 — the volume explained in cubic inches of a cylinder. Respectively, 71×6 meant 426 inch3, which, translated into cubic cm, gave exactly the same cylinder capacity. And, in fact, the first prototype trucks from Yaroslav had the very same American engine installed on them, without the pretense of being local. The engine had remained in the USSR on trucks that had been given as aid during the Second World War, and the Soviets were not ashamed to copy it after 1945 and start testing prototypes of KrAZ 214 trucks by 1951.

In the end, the launched engine was kept almost identical. Being a two-stroke engine, it had no intake valves, the air being delivered to the cylinders by means of a mechanical compressor through intake jackets directly into the cylinders. The engine had an unprecedented efficiency for that time, without a turbine, from only 6.97 liters of displacement, delivering 205 hp. Instead, it consumed 65 litres/100 km in an easy mode and over 100 litres/100 km when it was made to tow heavy vehicles.

However, the Soviets did not manage to ensure the same manufacturing precision of the two-stroke diesel engine back then, so it was noisier, and the noise also came from greater frictional forces, which also generated more heat. Precisely because of this, the drivers of this KrAZ had to always monitor the engine temperature.

Later on the KrAZ 255B was switched to another 4-stroke V8 engine, but the Americans at Detroit Diesel kept this 2-stroke diesel engine, first released in 1938, for many more years. In fact, they perfected it and they created all kinds of versions, including turbocharged ones, keeping versions with this displacement of 71 inches per cylinder, but also creating poses of 92 inches per cylinder. In fact, one of the most famous American trucks of all time, the famous Peterbilt 352 Pacemaker, had such a pose of the same 6.97 liter two-stroke diesel engine under the hood, similar to the KrAZ truck produced in Kremnchuk!

Foto: Camion Peterbilt 352 Pacemaker

It is interesting that for a while such KrAZ 214B trucks were exported, with engines whose official power was rated at 225 HP at 2,000 rpm, but indicated the same towing capacity of 50 tons. Such specimens were few in number and little information was preserved about them. It is interesting that a large part of the exports were made as military trucks, the same truck also serving as a chassis for a special vehicle with a mechanized bridge installation. Exports were made to almost all countries in the Eastern bloc of Europe, but also to North Korea, Cuba, Vietnam, Pakistan and Egypt. In the archives of the factory in Ukraine today, it is mentioned that during the 10 years of production in its premises, 32,870 copies were manufactured, of which 2,867 were exported.