The MÁV class 601 (nicknamed as "The Giant" or "Big boy" ) is a class of Hungarian four cylinder Mallet -type locomotives, which was designed to haul long and very heavy cargo on very steep railway tracks. With their 22.5 meter length and 2200 KW power, they were the largest and most powerful steam locomotives which have ever built before (and during) the First World War in Europe.
Based on the good operating experience with the series 651 more powerful locomotives arose at the MÁVAG in Budapest from 1914 on, which were especially provided for the line from Karlstadt (today: Karlovac, Croatia) to Fiume (today: Rijeka). By utilisation of the permitted axial load of 16,5t a locomotive was developed, which alone could move freighttrains uphill even on the steep line in the croatian karst without a banking engine.
Frame and chassis
The required traction power required a very large boiler, so an additional running wheel was placed in front of the six coupled bikes. The coupled bikes were therefore mounted in triplicate in a separate frame in accordance with the Mallet system, while the running wheel was mounted in the front frame as an Adams-Webb type axle with a lateral offset of 42–42 mm. In addition, the rear (driving) wheel of the front frame (i.e. the locomotive's fourth wheel) was turned thinner, and the front (locomotive's fifth) wheel of the rear frame was allowed to move laterally by 12–12 mm. The driven axles were made of 3% nickel steel, while the coupled and running axles were made of liquid steel. The axles of driven and coupled bicycles were completely drilled along the axle line. The suspension of the driven wheels, which were riveted together from 28 mm thick solid iron plates and embedded in an internally arranged frame, was connected by dowels. The first, second and fifth wheels were also fitted with tyre lubricators. The two parts of the frame were connected by the so-called Mallet pin. The complete boiler was mounted on the rear frame - the rear frame extended forward over the front frame to support the front of the boiler - and the cab (in the parlance of the time, the 'locomotive galley'). The extension of the rear frame section rested on the front frame section via a sliding plate. The front frame section could pivot laterally around the Mallet pin, and the straightening and 'anti-snaking' was provided by plate springs.
Engine
The rear frame wheels were driven by high-pressure cylinders and the front by low-pressure cylinders. The steam from the high-pressure cylinders was discharged through the cross-flow tube into the common flow tube, which also served as a receiver, and was fitted with a ball joint at the rear. From the transfer hose, the steam was discharged into the piston chambers of the low pressure cylinders. In each frame, the rear of the nickel-steel rims was the actuator. The right-hand cranks were wedged 90° forward on the wheel axle compared to the left-hand cranks. The piston rod was not a through rod on the rear, only on the front. The piston rod sleeves at the rear of each machine had a Schmidt-type metal seal, while the front of the front machine had a closed bushing. The crossheads were two-wire. The drive and coupling rods were of I-shaped cross-section.