New Zealand Government Railways 2-4-4 Locomotives in New_Zealand

Class M - rebuilt (Locobase 5179)

Data from John Garner's comprehensive site at [] ... (October 2002)

A decade after the NZGR took over 4 Otago 0-6-0 tanks, the shops at Addington rebuilt by removing a driven axle, replacing it with a trailing bogie with closely spaced axles, and adding a leading truck. As Garner notes, the adhesive weight was cut nearly in half. At the same time, the data show us, the cylinder size was cut slightly but the boiler pressure raised. The result is more nominal tractive effort, but a much more slippery engine.

Garner doesn't hazard a guess as to why this makeover seemed necessary. If you look at the factor of adhesion on the earlier arrangement (over 6), however, you see what must have been judged as a lot of weight going to waste. Reducing adhesion might not have had a dire impact and adding auxiliary axles front and rear may have offered more flexibility.

Until their retirements in 1924-1928, the Ms were used primarily as helpers on the grade or switchers in the yard.