Since diesel engines were still very heavy in the 1920s, the Reichsbahn also procured various railcars with benzene engines. Some two- and four-axle examples of these vehicles with riveted car bodies, later also referred to as “heavy-duty versions”, were built in 1926. The four two-axle vehicles were given the operating numbers 701 to 704. The designs envisaged railcars weighing around 20 tonnes with a large compartment for 50 people. With regard to the engine, transmission and other components of the machinery, the aim was to use only commercially available and tried and tested components from truck construction. This was not only intended to reduce manufacturing costs, but also to enable maintenance and repairs to be carried out by regular truck workshops.

A four-stroke benzene engine with six cylinders took over the propulsion, which drove one of the two axles via a mechanical transmission. The engine was housed in the car body and there was a cooler on each end. The gearbox was below the passenger compartment. Due to the use of two types of gearboxes and some other assemblies that were designed differently on a trial basis, each vehicle had a different curb weight. What was special was that the power lever only actuated an electropneumatic circuit that controlled the engine and transmission. This system was developed by AEG exclusively for these railcars and their four-axle relatives with the numbers 755 and 756.

The four vehicles were mostly used in the area of Frankfurt (Oder) or the now Polish towns of Pyritz and Meseritz. Later, a second-class compartment and a toilet were installed, thereby reducing the third-class space. After the end of the war, three of the four cars had already been written off as losses and only number 702 was still available on the territory of the East Reichsbahn. This was no longer used, but was only scrapped in 1957.

A four-axle variant was also developed in parallel with the two-axle railcars 701 to 704. The two locomotives received the numbers 755 and 756. With otherwise almost identical technical equipment, one can say that it is a double version of the two-axle variant. On each side was a six-cylinder benzene engine arranged lengthwise in the driver's cab, which drove the inner axle of the bogie below with mechanical transmission. Around 1930, an additional cooler for each engine was retrofitted on the roof, since the area of application was also in mountainous areas and the rear engine in particular could be cooled better in this way.

Here, too, two different transmissions were tested, so one vehicle received two WG 70 transmissions from the National Automobile Society (NAG) and the other two so-called Mylius transmissions with gear preselection. Doubling the power but significantly less than twice the weight resulted in a better power-to-weight ratio, whereupon the top speed was set a little higher at 60 km/h. With an offer of 65 seats, the capacity was not significantly larger than that of the smaller version. However, from the beginning there was a third-class compartment next to the open fourth-class compartment and a toilet. After a later remodeling, the open compartment was offered as a third class, while one second-class compartment was available.

As with the sister model, no series production followed. The reasons for this are that in the years that followed, more and more lightweight railbuses and heavier railcars with diesel engines appeared, against which these “heavy versions” with benzene engines could not hold their own. One prototype each was housed in Delitzsch and Kassel. The Delitzsch vehicle fell victim to a fire in 1932 and was scrapped. The other example was initially retired at the beginning of the war for economic reasons, but was eventually converted to run on liquid gas and put back into service. However, it did not survive the war without major damage and was subsequently scrapped.

The Furka-Oberalp-Bahn designated two petrol rack railcars that were delivered in 1927 as BCm 2/2. They were supposed to handle all services during low-traffic times and had a toilet and a mail compartment, while the rear cab was used as a luggage compartment. The rack drive and the adhesion drive could not be decoupled from each other. They were also referred to as BCZm 2/2 by the Railway Department.

However, the performance was not convincing, which was mainly attributed to the lack of experience with transmissions in railway vehicles with combustion engines. A maximum of one two-axle car could also be carried, which significantly increased travel times. With electrification in 1941, they became superfluous, although the first was used as a service vehicle for a while and passed to several new owners in the following decades, remaining inoperable. The other was sold to the RhB and used without rack drive until 1956.

In 1904, William Riley McKeen, once the superintendent in charge of vehicle procurement for the Union Pacific, had the idea of a gas-powered, streamlined railcar. Inspired by shipbuilding, he designed a shape that was tapered at the front and rounded at the back. Prompted by the then CEO of UP, the McKeen Company was founded to put this idea into practice. It was hoped that the petrol-powered railcars would be cheaper to operate than steam locomotives and the high acquisition costs and operational limitations of a battery railcar were to be avoided. The first, still two-axle vehicle was completed in 1905 and this was soon followed by a series of four-axle vehicles, which were ordered in large numbers by many operators in the USA.

The body was offered in two lengths of 55 and 70 feet and the interior could be fitted with either a large or small mail and luggage compartment or complete with passenger seats and a smoker's compartment at the rear with panoramic views. The windows were shaped like portholes and thus adapted to the ship-shaped car body. The engine also came from shipbuilding and stood directly on the front bogie. Only one axle was powered via the mechanical power transmission, which in combination with the low torque of the engine made for poor starting performance. From the eighth vehicle, a self-developed engine was installed, which now had 200 or 310 instead of 100 hp. There was no gearbox with reverse gear to change direction, but the camshaft could be shifted like on ships. This made it possible to run the engine in reverse after it had been stopped.

Side view of the 70 feet variant

Railway and Locomotive Engineering, September 1909

A total of 152 vehicles were built, of which 32 went to the Union Pacific and 31 to the Southern Pacific. From 1910 they also were exported. Two units went to Australia to the Victorian Railways and were delivered with a gauge of 5 ft 3 in. Five units were also delivered to the Queensland Railways with a gauge of 3 ft 6 in. Over time it became apparent that mounting the engine on the bogie was becoming a problem for the railcars. Since this was nearly unsprung, all impacts took their toll over time and made more and more vehicles inoperable. As a result, production ceased in 1917 and the Union Pacific dissolved the McKeen Company. Many railcars were later converted to passenger coaches and by the end of the 1930s there were almost no longer any engines on the road. The only example still running today belongs to the Virginia and Truckee Railroad and uses a modern drive train.

For rural, low-traffic lines of the South Australian Railways, J.G. Brill developed the railcars of the models 55 and 75. They differed on the one hand by different lengths and on the other hand by petrol engines with an output of 68 and 186 hp, respectively. The 75 model was also combined with a trailer. They were used almost all over South Australia and were called “Barwell Bulls”. Later, all received more powerful diesel engines. They were replaced by Bluebird and Redhen railcars in rural areas in the 1950s and then used in the suburbs of Adelaide until 1971.

Tatra developed the vehicles, also known as “tower railcars”, to transition passenger transport on branch lines and narrow-gauge railways with low passenger density from steam to internal combustion engines. Designer Hans Ledwinka's idea was to simplify operation and reduce costs with a single, elevated driver's cab. Its chassis corresponded to a two-axle goods wagon and the engine was suspended in the middle. The driver sat above the engine on a rotating chair from which he could see both directions of travel.

Most variants were powered by a petrol engine with an output of between 65 and 120 hp, which was connected to a four-speed gearbox and drove one axle. A conventional reversing gear was installed in the first variants. Later, engines with two camshafts were used, which could turn in both directions and thus made it possible to drive forwards and backwards. The tanks were arranged on the roof in front of and behind the cab. Depending on the engine power installed and the route profile, up to two specially developed trailers could be attached.

The first construction lot from 1928 included three different types. The M 120.3 series with 36 seats and an overall length of 9.20 m, which reached 55 km/h and of which a total of 27 examples were built up to 1930, was created for passenger transport on standard-gauge routes. At the same time, the M 140.1 series for express freight traffic was created, which was only 5.80 m long, was the fastest variant at 70 km/h and was only built four times. Furthermore, the M 11.0 series, which was somewhat narrower and shorter than the M 120.3 series, was built nine times for the Bosnian gauge of 760 mm.

The variants built later were all passenger railcars in standard gauge, which were between 10.53 and 10.70 m long and had a higher engine output. It all started with the M 120.4 series, of which 89 examples were built between 1930 and 1935. They initially had 100 and later 120 hp and were 60 km/h fast. A total of 63 examples of the M 130.2 series were built between 1933 and 1937 with the same dimensions and power data, but a new interior design. At the same time, the M 130.3 series was created, 30 of which had a diesel engine with initially 120 and later 125 hp and were otherwise almost identical to their sisters.

The vehicles were distributed to many branch lines within Czechoslovakia. After the annexation of the Sudentenland by Germany and World War II, some vehicles were removed from their ancestral territory. Just some of the narrow-gauge railcars of the M 11.0 series made it to Austria and later others were on Hungarian or Romanian territory. The majority of the vehicles remained in Czechoslovakia after the end of the war. With the introduction of the modern railcars of the M 131.1 series, the M 120.3 series was at first phased out by 1949. The M 120.4 series lasted the longest, the last examples of which were parked in 1965.