John believes it originated with a York-based Triumph dealer but from then on it’s variously described as possibly a Norton or even a Honda.

Its original registration states that it is a ‘Jax Special’.

Mr Mongomery said: “It looks like a Seeley Mk.II or is maybe a little Rob Northish but it is neither. My investigations show that a Triumph dealer in York in the 1970s produced this machine.

“There is a company called Jax Motorcycles in York. I have spoken to the guys there and they are now Yamaha dealers. They bought the company from the owner who passed away some five years ago. He was a Triumph dealer in the 1970s in York called Jack Cawthorne. My machine was originally described as a Jax Special when it was originally registered.

“York council archives have an entry which reads ‘YVY 38 – Jax Special – Bicycle – 650cl – 101901 – T110 D151 – 16/7/1971’.

The 101901 is the frame number and it was fitted with a 1960 Tiger pre-unit engine.

It has many changes through its life.
“In fact the V5 says it’s a Honda.

“In 1977 the DVLA records detail changes on March 1, 1977, turning it from a Norton to a T4. The engine changed to CB750E 2032125 – the ‘1’ might not be there since the photocopy is bad.

“It is decribed as rebuilt in the ‘for the official use only’ section. I wonder if someone wanted a special frame for his Honda engine? The reason for keeping the reg number as 1971 is that it’s tax free and 1977 would not be.

“Next change of owner was on March 13, 1977. Twelve days later the documents show a change from T4 to Honda. In 1980 the bike received another engine change to CB750E 1108538.”

He said changes of owners continued until September 1, 2002, where the engine changed to its current one – a 1964 Triumph 650.

“My first question would be, have you any record of or have you heard of a Jack Cawthorne making frames – Jax specials?”

If you can help, contact John at jwauctions@e-mile.co.uk