Top : Square Four 4G Mk1 1952 Bottom : Square Four 4G Mk11 997cc 1957 McIntosh
After the war the factory produced an uprated version in 1948 , with telescopic forks . In 1953 the 4G Mk11 had a new cylinder head with four instead of two down-pipes . Power had been raised to 40bhp at 5000rpm . This raised top speed to 105mph ( 169km / h ). Many believe that had Ariel taken seriously the suggestion that liquid-cooling would have solved the over-heating problem with the rear cylinders , which had plagued the model throughout its life span , things would have been very different . There are countless examples of motorcycles with rear cylinders presenting overheating problems , and it was liquid-cooling that ultimately solved the problem . Ariel joined the BSA group in 1958 , which turned out to be the beginning of the end for the Square Four . Wisdom , at the time dictated that four-stroke engines should be dropped in favour of two-strokes . What followed was the production of the Leader , a commuter two-stroke , which would bring to a close almost thirty years of a brave experiment that will be remembered fondly by anyone who ever rode one . It is
KIWI RIDER 85