The Hymeks (I speak from direct experience) were pocket rockets that could perform far better than their physical size implied. They were also very good riders, probably the best of the Hydraulics and I would suggest better than any other UK Bo-Bo on those long wheelbase bogies, and had very comfortable and warm cabs; their replacement on the 90mph 00.35 Cardiff-Peterborough parcels by the risible class 25s was a brutal shock to body temperature, eardrums, and spinal columns. Anyone who saw (or heard!) one lifting over 900 tons out of Aberthaw Cement Works on a dry rail would be somewhat re-assured about their ability in the South Wales coalfield, especially as IIRC the D7101 series were to be lower geared as replacements for the 56xx, another pocket rocket...
But I have doubts that a B-B would have really cut the mustard in the Valleys rough and tumble; the 37, with it's relatively light weight (for a diesel electric, it was still 2 coal wagons heavier than a Hymek) and 6 driven axles, performed very well in the event. One of the reasons for Beyer Peacock going under was that they had laid out cash on the materials for the D7101s but had to wait for delivery for payment from BR. This was during the middle of a loco supply crisis on the Western caused by problems with the Warships blocking bays at Swindon and teething/delivery problems with the Westerns, and was in the nature of a last straw. Fortunately for the WR, EE were in a position to supply class 37s quickly, and they were a proven success already on the ER and NER. The Hydraulic experiment was holed below the water line, and the WR's further type 4 requirements were met by Brush/Sulzer class 47s.
I rather liked Hymeks!
Edited by The Johnster, 23 February 2018 - 16:22 .