| Pennsylvania Railroad M1 |
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PRR M1a on display at the 1939 World's Fair. Pipe on the smokebox and box behind stack are components of the feedwater heater. |
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| Specifications |
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Configuration:
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| • Whyte | 4-8-2 |
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| Gauge | 4 ft 8+1⁄2 in (1,435 mm) |
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| Driver dia. | 72 in (1.829 m) |
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| Wheelbase: | |
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| • incl. tender | 79.32 ft (24.18 m) |
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| Length | - Loco: 54 ft 11 in (16.74 m)
- Tender: 52 ft 11 in (16.13 m)
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| Width | 10 ft 0 in (3.05 m) |
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| Height | 15 ft 6 in (4.72 m) |
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| Axle load | 67,750 lb (30,700 kg; 30.7 t) |
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| Adhesive weight | 271,000 lb (123,000 kg; 123 t) |
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| Loco weight | 390,000 lb (177,000 kg; 177 t) |
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| Tender weight | 378,360 lb (172,000 kg; 172 t) |
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| Total weight | 768,360 lb (349,000 kg; 349 t) |
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| Water cap. | 22,090 US gal (83,600 L; 18,390 imp gal) |
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| Tender cap. | 31.5 short tons (28.6 t; 28.1 long tons) |
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| Firebox: | |
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| • Grate area | 69.90 sq ft (6.494 m2) |
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| Boiler | 84+1⁄2 in (2,146 mm) |
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| Boiler pressure | M1a: 250 psi (1.72 MPa),
M1b: 270 psi (1.86 MPa) |
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| Cylinders | Two |
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| Cylinder size | 27 in × 30 in (686 mm × 762 mm) |
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| Valve gear | Walschaerts |
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| Valve type | Piston |
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| Performance figures |
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| Maximum speed | 70 mph (110 km/h) |
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| Power output | M1a: 4,034 hp (3,008 kW) |
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| Tractive effort | M1a: 64,550 lbf (287.1 kN),
M1b: 69,700 lbf (310.0 kN) |
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| Factor of adh. | M1a: 4.20,
M1b: 3.89 |
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| Career |
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| Operators | Pennsylvania Railroad |
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| Class | M1, M1a, |
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| Number in class | M1: 201, M1a: 100 |
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| Numbers | M1: 6699, 6800–6999, M1a: 6700–6799 |
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| Retired | 1957 |
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| Preserved | 1 |
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| Disposition | #6755 preserved, one tender preserved and set to be used on T1 new build, remainder scrapped |
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The M1 was a class of steam locomotive of the Pennsylvania Railroad (PRR). It was a class of heavy mixed-traffic locomotives of the 4-8-2 "Mountain" arrangement, which uses four pairs of driving wheels with a four-wheel guiding truck in front for stability at speed and a two-wheel trailing truck to support the large firebox needed for sustained power. Although built for both passenger and freight work, they spent most of their service lives hauling heavy high-speed freight trains. Many PRR men counted the M1 class locomotives as the best steam locomotives the railroad ever owned.
