Maine Central 4-6-2 "Pacific" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class C, C-1, C-2 (Locobase 6527)

Data from 1923 and 1924 Maine Central locomotive diagrams supplied by Allen Stanley in May 2005 from his extensive Raildata collection.

The first eight of this large class of Pacifics were designated class C. 450-451 (works numbers 42439-42440 in April 1907) were the lightest of the sixteen, showing an adhesion weight of 144,200 lb, an engine weight in operating condition of 222,600 lb, and 140,000 lb in a full tender.

The other six C class--452-457, works numbers 46036-46038 in March 1909, 47731 in June 1910, and 49205-49206 in February 1911) weighed as shown in this entry's spcifications.

The next five--458-462--designated C-1 (works numbers 50940-50941 in April 1912, 52985-52986, 53291 in March 1913) were the first to be delivered with superheaters. C-1s had only 8 sq ft (0.75 sq m) of arch tubes, trailed a heavier tender (146,500 lb) that had 7,500 US gallons, but weighed slightly less overall . Firebox heating surface area amounted to 183 sq ft (17.0 sq m), which combined with the tube and flue heating surface area for an evaporative heating surface area of 2,718 sq ft (252.5 sq m).

The last three--463-465--were dubbed C-2 (54568-54570 in March 1914). They put a bit more weight on the drivers (150,000 lb/68,039 kg). The center axle (which took the thrust from the main rod) turned inside journals that had 9 1/2" (241 mm) diameter and a length of 19" (483 mm), a sizable difference compared to the 9 x 12 (229 x 305 mm) journals of most of the earlier locomotives or even the 9 1/2" x 16" (241 x 406 mm) later fitted to 450-451. The 1923 diagram book shows a firebox heating surface area of 237.6 sq ft (22.07 sq m) that included 23 sq ft (2.15 sq m) of arch tubes.

All sixteen had 12" (305 mm) piston valves.

By the time of their retirements in the mid-1950s, most of the class had had the 8 sq ft of arch tubes (i.e., one arch tube) removed from the firebox in favor of 51 sq ft of thermic syphons. In addition to increasing direct heating surface area, the change raised overall heating surface area to the figure given in the specifications.

Class C-3, C-3B (Locobase 2803)

Data from 1923 Maine Central locomotive tables and diagram and MEC-PTC 4 -1956 Locomotive Diagrams supplied by Allen Stanley in May 2005 from his extensive Raildata collection. Works numbers were 57885-57887 in 1917 and 65554-65555 in 1924 . (Thanks to Chris Hohl for his July 2014 reporting the loaded tender weight. Chris also noted the class's trailing truck booster.)

These were the last five Pacifics bought by the MEC and they arrived in two batches -- three in 1917, two more in 1924. Cylinder volume increased considerably over the C, C-1, and C-2s (Locobase 6527) while boiler pressure was set 15 psi lower. Weights and tender capacities in this entry represent the first three as delivered in 1917. They had 14" (356 mm) piston valves and Ragonnet power reverse. The last two--designated C-3B--came seven years later.

Refits in 1933-1934 reduced cylinder diameter by an inch and increased boiler pressure rose to 195 psi; see Locobase 15893.

Class C-3, C-3B-24"" cylinders (Locobase 15893)

Data from MEC-PTC 4 -1956 Locomotive Diagrams supplied by Allen Stanley in May 2005 from his extensive Raildata collection.

In 1933, the Maine Central reworked the C class Pacifics that entered service in 1917 and 1924 (Locobase 2803), adjusting the balance between cylinder volume, boiler and firebox areas, and boiler pressure. They retained their 14" (356 mm) piston valves and the grate area remained the same. Cylinder diameter decreased by an inch; the 10 psi rise in boiler pressure didn't fully ameliorate the decrease in tractive effort. On the other hand, rearranging the firebox to hold two arch tubes totalling 12.7 sq ft (1.2 sq m) of arch tubes and two thermic syphons comprising 51.7 sq ft (4.7 sq m) of heating surface area contributed to more vigorous steam production. A further striving for efficient steaming came in the adoption of the Coffin feedwater heater.

The Waterville, Maine website (, last accessed 11 April 2008) carried an article by David Albert from 2006 in which he describes 470's service in greater detail:

"The 470 was built to handle the heavy 10 or 12 car passenger trains between Portland and Bangor. She operated on such trains as the (Flying Yankeeö, (Pine Tree Limitedö, (Bar Harbor Expressö. (The Kennebecö, (State of Maine Expressö and the (Gullö, an overnight Boston to St. John, New Brunswick train. The 470 also hauled trains on the Portland to Boston route over the Boston & Maine RR when the two roads were under joint management. It was not uncommon to see the 470 and other Maine Central locomotives at North Station in Boston during the period 1932 to 1953."

Specifications by Steve Llanso of Sweat House Media
ClassC, C-1, C-2C-3, C-3BC-3, C-3B-24"" cylinders
Locobase ID6527 2803 15,893
RailroadMaine Central (MEC)Maine Central (MEC)Maine Central (MEC)
Number in Class1655
Road Numbers450-465466-470466-470
Number Built165
Valve GearWalschaertBakerBaker
Locomotive Length and Weight
Driver Wheelbase (ft)131313
Engine Wheelbase (ft)33.6733.6734.34
Ratio of driving wheelbase to overall engine wheebase 0.39 0.39 0.38
Overall Wheelbase (engine & tender) (ft)6768.5068.50
Axle Loading (Maximum Weight per Axle) (lbs)
Weight on Drivers (lbs)146,800159,900177,200
Engine Weight (lbs)228,000268,300280,600
Tender Loaded Weight (lbs)140,000157,000190,800
Total Engine and Tender Weight (lbs)368,000425,300471,400
Tender Water Capacity (gals)700080009200
Tender Fuel Capacity (oil/coal) (gals/tons)111413
Minimum weight of rail (calculated) (lb/yd)828998
Geometry Relating to Tractive Effort
Driver Diameter (in)737373
Boiler Pressure (psi)200185195
High Pressure Cylinders (dia x stroke) (in)22" x 28"25" x 28"24" x 28"
Tractive Effort (lbs)31,55937,69736,619
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.65 4.24 4.84
Heating Ability
Firebox Area (sq ft)226273311.70
Grate Area (sq ft)50.2056.5056.50
Evaporative Heating Surface (sq ft)276129733033
Superheating Surface (sq ft)574636636
Combined Heating Surface (sq ft)333536093669
Evaporative Heating Surface/Cylinder Volume224.12186.89206.88
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation10,04010,45311,018
Same as above plus superheater percentage11,74712,33412,890
Same as above but substitute firebox area for grate area52,88459,59671,114
Power L117,89014,23716,693
Power MT806.01588.88623.05


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