Northern Pacific Challengers

The Northern Pacific ordered 21 "Challengers" from the American Locomotive Company in 1936 and took delivery of them during 1936 and 1937. These 4-6-6-4s were designated Class Z-6 and were assigned road numbers 5100 through 5120. They had four 23 x 32 cylinders, 69" drivers, a 250 psi boiler pressure, exerted 104,500 lbs of tractive effort and weighed 624,500 pounds.

In 1941, another six "Challengers" came from ALCO. These were designated Class Z-7 and they carried road numbers 5121 through 5126. They had four 23 x 32 cylinders, 70" drivers, a 260 psi boiler pressure, exerted 107,000 lbs of tractive effort and weighed 644,000 pounds.

The last steam locomotives bought by the Northern Pacific were the 20 "Challengers" it purchased from ALCO during 1943 and 1944. This group designated Class Z-8 was assigned road numbers 5130 through 5149. The Class Z-8 locomotives were very similar to the Class Z-7 except they were oil burners.

There are no surviving Northern Pacific "Challengers".

Class	Road Number	Year Built	Builder	Locomotive Weight
Z-6	5100-5111	1936	ALCO	624,500 lbs
Z-6	5112-5120	1937	ALCO	624,500 lbs
Z-7	5121-5126	1941	ALCO	644,000 lbs
Z-8	5130-5149	1943-44	ALCO	639.000 lbs

Specifications
	Class Z-6	Class Z-7	Class Z-8
Wheel Arrangement:	4-6-6-4	4-6-6-4	4-6-6-4
Length:	119' - 8"	119' - 8"	119' - 8"
Drivers:	69" dia.	70" dia.	70" dia.
Weight on Drivers:	435,000 lbs	448,500 lbs	435,500 lbs
Locomotive Weight:	624,500 lbs	644,000 lbs	639,000 lbs
Locomotive & Tender Weight:	1,023,000 lbs	1,081,000 lbs	1,081,000 lbs
Grate Area:	152.3 sq ft	152.3 sq ft	152.3 sq ft
Cylinders (dia. x stroke):	(4) 23" x 32"	(4) 23" x 32"	(4) 23" x 32"
Boiler Pressure:	250 psi	260 psi	260 psi
Tractive Effort:	104,500 lbs	107,000 lbs	107,000 lbs
Tender Capacity:
Water:	20,000 gals.	25,000 gals.	17,000 gals.
Coal:	27 tons	27 tons	? tons

Northern Pacific Challengers

References