Class M-2 - compound (Locobase 352)

Data from GN 1916 Locomotive Diagram supplied in May 2005 by Allen Stanley from his extensive collection.

Similar to Southern Ls engines, these M-2s were heavier, and had slightly smaller drivers, smaller boilers with GN's trademark Belpaire fireboxes, lower superheat ratio, and a different assortment of tubes. Fitted with Emerson superheater of 1,777 sq ft in the tubes, which was soon removed. and a feedwater heater. The specifications show the locomotives after the Emerson superheater was removed.

Some were simpled; see the M-2 simple entry (Locobase 2800). 22 were converted in 1929-1931 to 69"-drivered 2-8-2s and designated O-7s.

Class M-2 - simple (Locobase 2800)

Data from GN 1- 1929 Locomotive Diagram supplied in May 2005 by Allen Stanley from his extensive collection.

One of the few classes of locomotives delivered with the odd 2-6-8-0 arrangement. Drury (1993) speculates that it was adopted as a way to get more adhesion. As delivered they were M-1 compound engines (see Locobase 352) , but they were simpled in 1921. In keeping with their unusual arrangement, the rebuild gave them front cylinders 22" in diameter, the rear ones 23 1/2". See Larry Bohn photograph (http:/www.prostar.com/web/gngoat/gn27013.htm) for an illustration of the rebuild.

Charles R. Wood, in Lines West (New York: Bonanza Books, 1967), comments about these engines (p 66): "Essentially, [they] were slow-speed locomotives and any attempt to push the speed was hard on the engine and track." Watching the side rods carve great swaths of space close to the ground led some enginemen to dub them "grass-cutters." Wood continues: "Rough -riding at any speed above 25 mph, they vibrated with a fierce clatter of gangway plates and jingle of cab gauges. As one engineer put it, 'I couldn't even keep my shoelaces tied.'"

Under another photo of the M-2 on p 67, Wood attributes the roughness to large counterweights on the last set of drivers under the cab. And the lack of trailing truck meant that a backing M-2 "...met every rail joint and switch point head on, and changed the angle of direction with a very positive lurch." Yet, Wood concedes, these engines had their place in the GN's scheme of operations:

"[W]ith all their faults, they could move tonnage - not very fast to be sure - but between Butte and Great Falls they would come slogging up the grade under a vast canopy of smoke and cinders while the front bandstand articulated to the curves and the exhaust bounced off the hills and mountainsides."

By the end of the decade, 22 had become O-7 Mikados.