They commissioned Matt Wright, former New Imperial designer, to do a complete redesign. The result was a water-cooled version with barrels and cylinder heads cast in pairs, and fitted with enclosed valves. All exhaust ports now faced rearwards. Initially a thermo siphon design with a radiator on each side of the front frame downtubes, an impeller type water pump was soon added to the left side of the crankshaft to further aid cooling. Supercharger boost was reduced to 6 psi. Instead of the previous pressure lubrication, oil was now added to the fuel. The new duplex frame had integral rear plunger suspension housings, and the Webb-type girder forks were now graced with a deep finned alloy TLS front brake. The bike used a front tyre, and a rear. It had a six imperial gallon fuel tank. In May 1939 A R (Bob) Foster entered one in the North West 200, but it flooded on the start line. At the 1939 Isle of Man TT two bikes, ridden by Walter Rusk and A R (Bob) Foster, were 11th and 13th in the Senior TT and the supercharged BMW 492cc Type 255 Kompressor of Georg Meier and Jock M West took the first two places. Though capable of high speeds, the AJS V4s did not handle well, and blew head gaskets in practice. At the 1939 Ulster GP, the last GP before the War, the two bikes led from the start against Nortons and a supercharged four-cylinder Gilera, but halfway round the first of the laps, already timed at on one section, A R (Bob) Foster retired with plug trouble. Rusk completed the first lap at a record breaking average of and a lead of 34 seconds. On the third lap a fork link broke forcing retirement. It is believed that this was caused by mistaken fitment of a 7R fork link instead of the stronger V4 part during servicing. In 1939 the . dry sump V4 was the first bike to lap the Ulster Grand Prix course at over . Then World War II intervened. In June 1946, the AJS V4 finally won, at Chimay in Belgium, ridden by the same Jock M West who had defeated the AJS on a BMW in the TT before the War, and was now AJS Sales Manager. Walter Rusk did not survive the War, and Jock's mount was the bike Rusk had ridden. A week later at Albi, France, Jock West was in the lead when a crankpin seized and locked.