The first Sisu with British made Leyland engine came already in 1948. From the early 1950s Leyland was virtually the standard power source in Sisu's for during the following three decades; about 30 different types were in use. Some of the types were very robust but also technically failed units appeared with repeating problems; the Leyland O.801 V8 diesel is particularly mentioned as one of the worst. By the early 1970s Leylands had remained too weak for the increased permissible vehicle total weights in Finland.