The Norton Manx "Double Knocker" became the engine to have in 500 racing. Official output was about 50 hp, 10% more than the JAP but specialist tuners managed significantly greater figures. The downside was (and is) the much higher cost and limited availability. Steve Lancefield and Francis Beart became the tuners of choice for the Norton.

The Manx was originally designed in 1927 by Norton’s Chief Designer, Walter Moore. A long stroke (79 X 100mm) overhead cam single, it was reliable and powerful enough to bring Norton success at the Isle of Man in that year. Joe Craig took over responsibility for the racing department and, in 1938, modified the valve gear operation to “double knocker” form.

Through the years, a number of developments were introduced including a combined, forged, main shaft and flywheel, additional piston rings, and the introduction of an all aluminium head. The stroke was reduced several times during the fifties until Norton officially withdrew from racing in 1956.

Installed in a Cooper Mk IX

and installed in the back of a Kieft

"Servicing the Manx" reprinted from Motor Cycling April 1957 - Click Here (Warning large file unsuitable for dial up)