Diesel Locomotive Classes – Metre Gauge & Narrow Gauge

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Information on broad gauge diesel locomotives can be found on this page.

Metre Gauge Locomotives


Originally class 'DY', these were among the first MG main-line diesels, and were survivors from the second batch of North British diesel locos supplied in 1955. 25 of them were made originally. Paxman V12 RPHXL II engines developing 634hp, with L36R Voith hydraulic transmission. B-B bogies of welded construction. They were originally used by WR for goods haulage on lines near Gandhidham where water supply for steam locos was problematic. Many later transferred to SCR. CLW replaced the engines on these with Maybach engines (Mak/CLW L6 6M 282 A(K), 700hp) around 1975 (1974-1976 according to Hughes). These locos were phased out in the early 1990s.

YDM-1 class loco
YDM-1 Class. Photo courtesy Richard Cripps.
YDM-1 Specs
Builders North British Locomotive
Engine Paxman V12 RPHXL II; 634hp; 1250rpm max, 525rpm idle; 178mm x 197mm bore/stroke; compression ratio 16:1; centrifugal pump cooling system driven by a belt fan
Governor Hydro-mechanical
Transmission L36R Voith Hydraulic
Horsepower 634hp (542hp site rating)
Bogies B-B
Weight 43.6t
Starting TE 10.9 tons at 25% adhesion
Max. Speed 88km/h
Length Over Buffers 10630mm

41 of this class were built by CLW in mid to late 1980s. CLW-MaK 6M282 A(K) engines; 700hp delivered via a Voith L4R4ZU2 hydraulic transmission. These locos share many components and sub assemblies with other CLW diesels like the WDS-4, ZDM-4 etc. The shell is also a modified version of the ZDM-4A. All of them were at SCR's Maula Ali shed initially, but were transferred to Golden Rock on SR when the lines around Hyderabad began to be converted to BG. On SR, they were used to run commuter shuttles in the Trichy area to Kumbakonam. In the early 2000s, they were seen hauling passengers and freight on the Chengalpattu - Kanchipuram section before being scrapped.

YDM-2 Class
YDM-2 Class. Photo courtesy IRFCA Gallery.
YDM-2 Specs
Builders CLW
Engine MaK-6M28A(K) in line 6-cylinder 4-stroke; Brown Boveri HDC VTR 250 supercharger; 900rpm max, 440rpm idle; 240mm x 280 bore/stroke; compression ratio 12.2:1; Behr type hydrostatic cooling system
Transmission Voith L4R4ZU2 Type (Hydraulically reversible)
Horsepower 700hp
Axle Load 12t
Bogies B-B
Weight 48t
Starting TE 14.4 tons at 30% adhesion
Max. Speed 75km/h
Length Over Buffers 11000mm

GM (EMD) designs, model GA12, delivered between 1961 and 1962. EMD 576C 12-cylinder, 2-stroke engine delivering 1390hp. Bo-Bo, with EMD D49MC traction motors, 4.598:1 gear ratio. Towards the end of their life, they were based in WR handling branch line and freight duties around the Ahmedabad area. Sabarmati shed had the last 2 YDM-3's (#6073, #6074). Both these are now preserved at DLW. All were withdrawn from service in the mid 1990s.

YDM-3 Class
YDM-3 Class. Photo courtesy IRFCA Gallery.
YDM-3 Specs
Builders GM-EMD
Engine EMD 576C 12-cylinder, 2-stroke; GM Roots blower supercharger; 800rpm max, 275rpm idle; 216mm x 254mm bore/stroke; 16:1 compression ratio; centrifugal pump cooling system (907l/min @ 2245rpm), fan driven by belt (35hp @ engine rpm 800rpm).
Governor Woodward
Transmission Electric, EMD D-25 generator (800rpm, 1000V, 1710A)
Traction Motors EMD D49MC
Horsepower 1390hp (1259hp site rating)
Axle Load 11t
Bogies Bo-Bo
Weight 58.5t
Starting TE 14.3 tons at 32.5% adhesion
Max. Speed 80km/h
Length Over Buffers 13790mm

Workhorse MG diesel loco for IR. First units were built by ALCo between 1961 and 1964, later made by DLW (1968-1993). ALCo 251B (251D DLW) inline 6-cylinder, 4-stroke engine, 1400hp; Co-Co; DC-DC transmission; 12t axle load; Dynamic brakes; Vacuum train brakes initially, some dual systems later; Max speed of 100km/h (though there are reports of faster runs with crack trains like Pink City and Vaigai Expresses).

YDM-4 Class
YDM-4 Class. Photo courtesy IRFCA Gallery.

YDM-4A are identical to YDM-4, except that they were supplied by MLW (1964) – the Canadian batch consisting of about 99 locos. Some of the MLW locos did not have the 'A' suffix in the class designation. In later years, YDM-4A also designated locos equipped with both vacuum and air train brakes.

Initially, DLW exported some (15 each) of these to Tanzania and Vietnam (1976-1985), and to Bangladesh (2000?). The ones for Bangladesh were classed YDM-4BR and had dual cabs, a change achieved without modifying the length of the loco. This variant turned out later to have major cooling problems. DLW continues to export rebuilt YDM-4s to African nations. Malaysian railways (KTM) acquired 39 used YDM-4's from IR in 1996. It is not clear if they were leased or sold. Of these, 14 were returned to India by 1999. In Malaysia they retained their IR road numbers (between 6352 and 6725).

YDM-4 Specs
Builders ALCo, MLW, DLW
Engine Alco 251B-6 (Alco/MLW), Alco 251D-6 (DLW); 6-cylinder, 4-stroke, inline; ALCo 350B supercharger; 1110rpm max, 400rpm idle; 228mm x 266mm bore/stroke; 12.5:1 compression ratio; Cooling via centrifugal pump with an Eddy current clutch fan (41hp @ 1100rpm)
Transmission Electric; GE GT581, BHEL 10919 AZ traction generator
Traction Motors GE 761A3, BHEL 253 AZ
Horsepower 1400hp (1300hp site rating)
Axle Load 12t
Bogies ALCo Co-Co trimount
Weight 72t
Starting TE 18.9 tons at 26% adhesion
Max. Speed 100km/h
Length Over Buffers 15208mm

GM (EMD) design, model GA12, delivered between 1963 and 1964. Similar in most aspects to the YDM-3 (see above), except for a tweaked traction motor (EMD D69MC) and higher weight (69t vs 58t for YDM-3) to improve adhesion characteristics and tractive effort (21.7 ton starting TE at 31.5% adhesion). The first loco to be homed at Sabarmati shed was a YDM-5. All of them retired in the mid 1990s, with the last run being in February 1998 (#6098). This loco is now plinthed outside the GM's office at DLW.

YDM-5 Class
YDM-5 Class. Photo courtesy IRFCA Gallery.

For other specifications, refer to YDM-3 class above.

Narrow Gauge Locomotives


Built by Jung in 1956, these were the original class 'DZ' on NR (Kalka-Shimla Railway). Identical to NDM-1 (see below), but with 2'6" gauge. Twin MWM TRHHS 518S engines, 145hp each, mounted on either side of the cab. B+B arrangement like a Garratt. The two engines shared a common hydraulic transmission with dog clutches. All five were re-gauged to 2'0" gauge and converted to NDM-1 units and sent to the Matheran Light Railway later when the ZDM-3 locos became available (1972-1982). NR #704 was converted back to 2'6" and sent to Pragati Maidan, New Delhi to haul a short train at the exhibition centre. #704 was later moved to the NRM, where it is now preserved. All-India numbers #543-547 were allotted but never displayed on the locos. They are almost always referred to by their NR/KSR numbers #700-704.

ZDM-1 Class
ZDM-1 Class. Photo courtesy IRFCA Gallery.
ZDM-1 Specs
Builders Arn Jung
Engine Two MWM TRHHS 518S, inline 6-cylinder, 4-stroke; Brown Boveri VTR 160/26H supercharger; 1100rpm max, 500rpm idle; 140mm x 180mm bore/stroke; 19:1 compression ratio; Direct injection; Cooling via centrifugal pump with two belt driven fans (16hp @ 1540rpm)
Governor Bosch, centrifugal
Transmission Hydraulic, Twin Voith L33U
Horsepower 145hp (125hp site rating)
Axle Load 7.35t
Bogies B+B
Weight 20.3t
Starting TE 8.79 tons at 30% adhesion
Max. Speed 33km/h
Length Over Buffers 9524mm

25 of these B-B locos were supplied by MaK in 1964 to operate in hilly terrain like the KSR and Kangra Valley Line, but they eventually ended up working the most in the Nagpur area. Reverse governed Maybach 8-cylinder MD-435 engines, 700hp, Suri hydraulic transmission. Max. axle load of 8 tons. Many of these locos were rebuilt in the 80s and 90s and feature an "R" suffix to the class. It is believed these locos were fitted with a KPC made simplified hydraulic transmission instead of the failure prone Suri during their rebuild.

ZDM-2 Class
ZDM-2 Class. Photo courtesy IRFCA Gallery.
Builders Maschinenbau Kiel (MaK)
Engine Maybach MD-435 8-cylinder 4-stroke; Maybach AGL-85 supercharger; 1700rpm max, 660rpm idle; 185mm x 200mm bore/stroke; 16.2:1 compression ratio; Indirect injection via a Lagrange type pump; Cooling via centrifugal pump with one Behr hydro-static fan
Governor Maybach-Suri R321GF
Transmission Suri Hydro-Mechanical
Horsepower 700hp
Axle Load 8t
Bogies B-B
Weight 32t
Starting TE 10.5 tons at 33% adhesion
Max. Speed 50 km/h
Length Over Buffers 10244mm

There are two very different types of locos assigned this class! The original series was built by CLW between 1971 and 1982 and has a similar design to diesel locomotives made during that period. The newer locos, built by Parel Workshops starting in 2009 are completely different featuring dual-cabs, better engine and modern control and diagnostics. It is a mystery why these aren't designated as a new class.

The original ZDM-3 made by CLW have MaK reverse governed 6M 282 A(K) engines (700hp), with a Suri hydro-mechanical transmission. A later batch (made in 1980-81, #178-#197) have a simplified KPC made hydraulic transmission, but retain all other characteristics of the first batch. Many ZDM-3 were rebadged as ZDM-3A later, but it is not known what changes were made. 35t loco weight; 9.25t max. axle load with a starting TE of 10.5 tons at 30% adhesion. 10 ZDM-4 units (see below) were converted to ZDM-3 class by removing one axle from each bogie (numbers remained unchanged).

ZDM-3 Class (Original 1971-82)
ZDM-3 Class (Original 1971-82). Photo courtesy IRFCA Gallery.

In 2009, CR's Parel Workshops started manufacturing a completely redesigned B-B locomotive, still classified as ZDM-3 (RDSO has them listed as ZDM-3D, but all of IR's materials refer to them as ZDM-3 only). These locos feature dual cabs reminiscent of EMD models, 12-cylinder Cummins VTA-28L2 engines (800hp @ 2100rpm), with two Holset turbochargers, KPC hydraulic transmission, an "on demand cooling system", dual brakes, auto emergency braking (enforced at 10% higher than rated line speed), vigilance control device, cold start capabilities to start in Himalayan weather, and a TFT screen to display diagnostics and engine parameters. Max. axle load 9.25t. Max. speed 40km/h.

ZDM-3 Class (New 2009-)
ZDM-3 Class (New 2009-). Photo courtesy IRFCA Gallery.

Built by CLW, these are very similar to the ZDM-3, but have an extra axle (1-B-B-1) to reduce axle loading. The first lot had issues with excessive wheel slip and the locos were all converted back to ZDM-3 by removing an axle from each bogie. The ZDM-4A addressed these issues in the bogie and added an updated CLW-MaK 6M282 A(K) 700hp engine. The ZDM-4A also features a toggle device to limit the maximum tractive effort and prevent wheel slips. Voith L4R2U2 hydraulic transmission; 9.25t max. axle load; Loco weight of 38.5t.

ZDM-4A Class
ZDM-4A Class. Photo courtesy IRFCA Gallery.

The first batch ZDM-4A were allotted to the Barsi Light Railway, but they worked the lines around Nagpur later. Subsequent batches of these locomotives were badged rather confusingly as ZDM-4, though they had the improved characteristics. Further confusion was caused by sheds during overhauls not following a common scheme and badging them as either 4 or 4A. Working locomotives are found at the Pathankot shed, servicing the Kangra Valley Railway. A few are preserved at Nainpur, Murtizapur and Pathankot, while others have been scrapped or await condemnation (February 2022).

ZDM-4A Specs
Builders CLW
Engine CLW-MaK 6M282 A(K) inline 6-cylinder 4-stroke; Brown Boveri HDC VTR 250 supercharger; 900rpm max, 440rpm idle; 240mm x 280mm bore/stroke;12.2:1 compression ratio; direct injection; Cooling via centrifugal pump with one Behr type hydro-static fan
Governor MaK
Transmission Hydraulic, Voith L4R2U2
Horsepower 700hp
Axle Load 7t
Bogies 1-B-B-1
Weight 38.5t
Starting TE 7.8 tons at 30% adhesion
Max. Speed 50km/h
Length Over Buffers 10300mm

These locos were built to address needs of lines where the permissible axle loads were limited to 6 tons. They feature a Kirloskar-Cummins KTA-1150L 6-cylinder engine delivering 450hp. Voith hydraulic transmission, with drive to axles done by cardan shafts. 5.5t max. axle load; Max. speed of 50km/h. They were predominantly found in the Baroda area servicing the Dhaboi NG system, though in recent times, they operate trains out Dholpur. Four of these were sent to the Jayanagar Janakpur railway in Nepal in 1994. The NDM-5 is mechanically very similar, but on the 2'0" gauge.

ZDM-5 Class
ZDM-5 Class. Photo courtesy IRFCA Gallery.
Builders CLW
Engine Kirloskar-Cummins KTA-1150L, inline 6-cylinder, 4-stroke; 1900rpm max, 600rpm idle; 159mm x 159mm bore/stroke; 14.5:1 compression ratio
Transmission Hydraulic, KPC L4R2U2-450
Horsepower 490hp (450hp site rating)
Axle Load 5.5t
Bogies B-B
Weight 22t
Starting TE 6.6 tons at 30% adhesion
Max. Speed 50km/h
Length Over Buffers 8800mm

Articulated 2'0" gauge loco, mechanically similar to the 2'6" ZDM-1. Originally intended for the Kalka Shimla Railway (and classed ZDM-1), they were regauged and sent to the Matheran Light Railway when ZDM-3s became available for the former. The first one, #500, was ZDM-1 #543 (NR #700), regauged as an experiment. Three more ZDM-1 locos (504-506, ex-ZDM-1 #544-546, NR #701-703) were also regauged later. Three (#501-503) were supplied with original gauge 2'0".

NDM-1 Class
NDM-1 Class. Photo courtesy IRFCA Gallery.

The Parel Workshops have been making newer versions of these locos as a replacement for the older lot since 2015. These newer ones are air-brake only to match the rolling stock. It is not known what engines or hydraulic transmission these newer models use. #550 and #551 are badged as NDM-1A to indicate air-brake only.

For other specifications, refer to ZDM-1 class above.


2'0" gauge variant of the ZDM-5 class. Mechanically similar to its larger gauge brother, except that the first three NDM-5 had L2R2ZU2 hydraulic transmissions made by SAN Engineering. The rest of this class has KPC built L4R2U2-450 transmissions. Eleven were built between 1987 and 1989. Equipped with dual brakes, with many converted to air-brake only in the mid 2000s. These were used on the former Scindia Railway lines around Gwalior. With those lines undergoing conversion starting 2021, this class is expected to be scrapped soon. One, #804, is preserved at the Modern Coach Factory, Rae Bareli.

NDM-1 Class
NDM-5 Class. Photo courtesy IRFCA Gallery.

#812, #813 and #814 are new units built by Parel Workshops and feature twin cabs (like the ZDM-3 variant), a wider body than the original and modern loco features. These are air-brake only. Other specifications are not known.

For specifications of the older model, refer to ZDM-5 class above.


First introduced in 1997 as a replacement for the aging NDM-1 class on the Matheran Light Railway. Made by SAN Engineering, these are two-axle bogie less locomotives. Kirloskar-Cummins NTA-855L, 6-cylinder engine mated to a reversible Voith hydraulic transmission. Leaf springs are used for the suspension. The front suspension springs are inter connected by a compensating beam, which counter balances shock. Note: SAN (the manufacturers) in their documentation describe these as '0-B-0', which is plainly incorrect as these are 4-wheeled locos.

6 of these were ordered (#600-#605), with the first four destined for Matheran, and two for the Darjeeling Himalayan Railway. Around 2016, all were transferred to the DHR. #604 is named 'Maverick', #605 is 'Buccaneer'.

NDM-6 Class
NDM-6 Class. Photo courtesy IRFCA Gallery.
Builders Suri and Nayar (SAN) Engg. and Loco Co
Engine Kirloskar-Cummins NTA 855L inline 6-cylinder 4-stroke; Holset AR-3522294 supercharger; 2100rpm max, 600rpm idle; 139mm x 152mm bore/stroke; 13.5:1 compression ratio; Cooling via a belt driven centrifugal pump (518l/min)
Governor Mechanical variable speed built in fuel pump
Transmission SAN-Voith Hydraulic, L2r2zU2 turbo-reversible with 2-stage reduction in final drive gearbox
Horsepower 335hp
Axle Load 8.61t
Bogies None
Weight 17.23t
Starting TE 9.2t
Max. Speed 30km/h
Length Over Buffers 5848mm