Soviet State 4-8-0 Locomotives in Russia

Class M (Locobase 20639)

Data from D[ennis] Rock Carling, 4-8-0 Tender Locomotives (New York: Drake Publishers, Inc, 1972), p. 39-40 and serial 77 on table VI [6], pp.98-99. See also "Diagrams [of] Locomotives and 'Passports' [sic--meaning "tenders"]", published in Moskva (Moscow), 1935 p. 42-43, PDF supplied by Teemu Koivmaki in his 5 October 2019. (Many thanks to Teemu for sending what might never have fallen into Locobase's hands. An indispensable addition to Locobase's library.)

These "unmistakably Russian" locomotives nevertheless straddled the older Imperial tendencies and the new Soviet idea. Designed originally by Ravetsky (who died in 1924), this class was a home-built successor to the very useful 424 class locomotives supplied by Hungary to the USSR as reparations after World War I.

Ravetsky apparently intended to produce a three-cylinder compound locomotive, but after his death, other designers chose the all-high pressure layout that went into production. But Russian/Soviet locomotive designers tended to find unique solutions to common problems and in the Ms, they almost certainly over-innovated. Many of their choices seem to tried to solve problems caused by other design features.

One such was arguably the long coupled wheelbase for a 4-8-0. Long piston rods reached out from the cylinders and moved through two crossheads. One was located over the rear bogie axle and the other over the first driver. As Carling remarks, "Keeping both sets of slide bars in alignment must have been a fitter's nightmare." Even with that odd arrangement, the outside main rods measured 11 ft 3 1/4 in (3.45 m).

Locobase wonders what if any unfavorable consequences may have flowed from adopting two different diameters for the bogie wheels. The rear wheels measured an unusually large 1,320 mm (52"), the front a more typical 1,050 mm (41.625 in). Carling noted that the rear axle might be loaded more heavily because the spherical bogie pivot lay 55 mm (2 1/8 in) behind the center of the long bogie wheelbase, "but not so as to require wheels so much larger."

Valve gear arrangement featured both a second return crank on the upper end of the expansion link (rather than the more typical rocking shaft) on the left side. Another rocking lever linked the end of the radius rod with the top of the combination lever, Carling noted.

Two other noticeable characteristics were the locomotives' great height, the 3.45 m (11 ft 3 7/8 in) centerline measuring higher than all other European locomotives. The other was the large and quite rectilinear Belpaire firebox.

Despite these failings, Putilov produced 98-100 of the class in 1927-1930. Soon after M class engines entered service, their unsteady running put the 100 kph (62 mph) maximum speed mostly out of reach. Instead they were placed on slower trains.

Some were later refitted with two cylinders because of widespread problems with crankshafts (at times half of the stud was in the shop for repairs).