AJS 7R3 Tripleknocker

In the early 1950s, AJS needed a new race bike, the 7R was not delivering and the Porcupine was also nearing the end of its development. Development engineer Ike Hatch was put in charge of the next phase of the 7R development. What he came up with was an interesting three valve engine, one that used two exhaust valves arranged radially. This was done for several reasons, the radial arrangement would allow a better shaped combustion chamber with a centrally located spark plug, the two exhaust ports would in theory allow better airflow through the head and the two small valves cooled quicker keeping the incoming mixture cooler.  The valve actuation was inspired, to say the least. 

The engine was still recognizably a 7R, with the cam chain tower on the right side, but now it leaned back to drive just the intake cam. That cam was geared to a layshaft, which drove two individual exhaust cams running fore and aft- one to each exhaust valve. The drawing below shows an idea of the layout, I'd love to see it as an exploded view.

 In 1952 the bike was quite competitive but limited development meant that 1953 was less successful. In 1954, the engine remained much the same but the chassis was lowered and with much of the fuel tank below float bowl height, required the addition of a fuel pump. 

 That was the end, the factory decided to continue with production based 7Rs in 1955.