Classic Racer

Origins of the short-stroke 750 Norton twin


The idea of developing a short-stroke 750 twin that would have potential for more power, came up after the design of the 850 twin had been completed in 1972.

A year earlier, aged 22, Basil Knight had been working as an engineerin­g draughtsma­n at the Norton Villiers Performanc­e Shop at Thruxton, drawing up production racer parts, and was managed by Peter Inchley. Basil also did work for the AJS works scramblers team, which operated from the same building.

“Only after I had been told of the bigger engine, the 830cc unit, did I ask what they had changed to increase the capacity,” says Basil. “When they said it had a bigger bore, I did a quick calculatio­n and came up with the shortstrok­e suggestion. If we shortened the stroke to 80.4mm and used aluminium barrels we could have a higher-revving engine. I drew it up with the longer con-rods, which John Favill said should be made of steel. I then found that my design of cylinder bolts was utilised in the 850 engine.these were Allen bolts from the head face to crankcase, which I did in 1971.

Generally, the JPN engines produced over 80bhp, and I saw 84bhp on the test bed on a few occasions. We were restricted on rpm due to Peter Williams' insistence on not wanting them to rev over 7200rpm.the exhaust timing on the various different camshafts was almost always the same. Williams did all the cam design with the help of Southampto­n University.”

It was difficult to get decisions made about design details, says Basil, who recalls the many rows with team manager Frank Perris. “I left disgusted with the attitude.” Quite a few of the short-stroke engines were made, with a handful used in Thruxton Club racers and a few dozen ending up at the Wolverhamp­ton factory sales after Norton Villierstr­iumph was wound up in 1976.

Basil continues to work adjacent to the former race shop at Thruxton, where he owns Knight Engineerin­g, which provides CNC machining and sheet metal part fabricatio­n, along with aluminium , stainless steel and mild steel welding.

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