The description of the class 164A Garratt stated that, "It was on the RSR that the Garratt locomotive, like several other types, saw its final development." That statement was overtaken by events in 2010 and 2011. Artur Gorote's department, after several years of stagnation, caused mainly by the frustrations of the 465A and 675A projects, produced the Garratt design seen here. Gorote was also fortunate in being able to bring Albert Leaworthy, a former Beyer Peacock draughtsman, out of retirement for the duration of the development project. Gone are the tandem outside cylinders of the 655A, gone is the twelve-coupled rigid frame, gone is the long, slender boiler that taxed the exhaust to the limit, and gone are cylinders crammed up against the firebox. The advantages of the Withuhn-style opposed cylinder layout, which conquered at last the problem of balancing the reciprocating masses, are here combined with the excellent steam generating capacity of the short, fat Garratt boiler, which was retained almost unchanged from the 164A. The boiler is fitted with two superheaters of different sizes, the larger one supplying steam to the rear engine unit at a higher temperature to compensate for heat losses in the long live steam pipe. Each engine unit is a triple-expansion compound, the cylinders at the inside ends using high and intermediate pressure steam and those at the outside ends low pressure. This arrangement was adopted to minimise the distance travelled by the live steam. Krauss-Helmholtz trucks are fitted throughout. The design shows, unusually for these days on the RSR, Walschaerts valve gear; the reason for this was given as restricted space at the inner ends of the engine units.

Text and graphics © Norman Clubb 2011