Initial test-bed work was performed on a T150 engine which was first fired up on the 7th of December 1972. It was immediately apparent that locating the cam directly across the cylinder head between the inlet and exhaust valves prevented any easy access to the center spark plug. To gain access to the plug the cam box had to be removed!

RIGHT An early drawing of the cam and rocker layout.

As might be expected the main problems were sorting out the cam timing and the correct oil supply to the cam. Various cam and ignition timing settings were tested after the drive-side piston holed and cam faces were badly scored. The drive belt was strengthened to ensure more accurate valve timing. Oiling remained the main problem that needed attention, especially the supply to the cam and the lower belt pulley mounting. The latter causing the sudden destruction of one set of engine cases when it locked up.

LEFT Frontal view showing the belt drive, the distinctive rocker box inspection covers and the external oil feed pipe to the lower belt drive pulley shaft (in the place of the old exhaust camshaft) - the oil feed is taken from the main crankshaft oilway.

On the 10th of May 1973, after about three months of testing, a BSA A75 was prepared for road testing (incidentally, this was the same bike that later carried the four cylinder Quadrant engine). Throughout the summer of '73 the factory road testers, including Percy Tait, Fred Swift, Dave Pickering and J.C., logged some 3,000 miles.

Performance wasn't much different from a stock triple; power was "good" at low rpm and much the same as a stock bike elsewhere in the rpm range. Reliability was below average. There was a variety of fractured or broken parts: seat brackets, rear no plate brackets, brake levers and indicators. The cause seemed to be higher than usual vibration between 5,000 and 6,000 rpm. Fuel consumption was also below average at about 28 mpg.

RIGHT One of the prototype engines installed in a road bike in 1996. Note the elegant design with plenty of room and the neat tachometer cable drive from the end of the cam. Note also the painful access to the middle cylinder's spark plug - none!