Thompson's class L1 Adriatic suburban tank locomotives were another unsuccessful design. They were powerful machines that should have been well-suited to their duties but their 5 ft 2 inch wheels were too small for fast outer suburban services and they quickly knocked themselves apart. The axle boxes suffered, water tanks split, oil pipes broke off, and crossheads wore rapidly. Class B1 On the other hand, Thompson built one of the most successful LNER designs, the class B1 4-6-0, which was a simple two-cylinder design mixed traffic engine. The B1 was based loosely on Gresley's class B17. The prototype for the B1 was a B17/1 modified with a higher pressure boiler and with its centre cylinder removed. The design proved to be free-steaming, economical and simple to maintain, though some details caused issues in due course. The small amount of balancing of the reciprocating masses (in order to reduce hammer-blow) made for a rough ride and a significant degree of vibration in the cab, and eventually the reciprocating mass percentage was increased. More than 400 B1s were built between 1946 and 1952: British Railways continued B1 production after nationalisation. The Diagram 100A boiler used in the class formed the basis for the rebuilding of many pre-grouping classes, including the class O4 2-8-0 freight locos. The Thompson B1 equalled the LMS Black Five locomotives during the inter-regional exchange trials in the first year of British Railways. The B1 was also cheaper to build than the Black Five. The B1 had poor and very inconsistent ride quality, unlike the relatively smooth riding qualities of a number of Gresley designs, though it must be considered that fundamentally a locomotive with a rear truck/Cartazzi arrangement does generally ride better than one without, and even Gresley's classes reflected this. Poor riding remains a characteristic of the two preserved B1s. Other Rebuilds Thompson also rebuilt a number of different Gresley locomotives, usually using the B1-derived boiler (in turn developed from the B17 type boiler) and 2 20" cylinders (derived from the early Gresley A1 engines). The Robinson 8K (LNER O4) was re-boilered and re-cylindered to create the class O1. Two B17's were rebuilt with 2 cylinders to create the prototypes for the B1 class, and later more B17s were converted. A K4 became the prototype K1/1 and a K3 became the K5. The K1/1 was a particularly unpopular engine: its name MacCailin Mor was not a good