The 38th Carole Nash Bristol Classic MotorCycle Show takes place at the Royal Bath & West Showground in Shepton Mallet this weekend, and there’s one very special local bike you should check out on the Carole Nash stand.
Proudly on display…
The only surviving HRD Model P to be fitted with a 500cc Cross rotary valve engine will proudly be on display. The bike, which was rolling test bed for Bath engineer Roland Cross’ innovative rotary valve engine, is the only example of the Cross engine that is still known to be in working order.
Cross purchased a complete rolling chassis from HRD in August 1934 and fitted his innovative engine, which was built upon a Rudge bottom end. The bike became famous for its staggering performance. The Cross HRD was capable of almost 100mph and a small number of engines were built for customers to fit to their Rudges and Royal Enfields.
Replacing poppet style valves
The main innovation of the Roland Cross’ engine was the adoption of rotary valves, which he believed could replace the more common poppet style valves. While that would not immediately be the case, the technology has been trialled on Formula One engines in recent years, while Honda’s current flagship CRF450R uses a rotary valve design which they claim offers more power and torque from a lighter and more compact cylinder head.
While the initial Cross engines proved to be more powerful than the other engines of the day, this in turn created a problem as off the shelf cast iron piston rings broke under the additional stress and damaged cylinder after cylinder. Despairing, Roland was heard to mutter “If I cannot buy rings that don`t break, I will design and make my own” which this he did. Taking round, drawn wire of an appropriate diameter from a specialist manufacturer he designed and made his own rolling machines to transform the round wire to rectangular section and then designed and developed a hot coiling process so that the longitudinal grain flow became circumferential. Following some rather special and innovative heat forming a piston ring was produced that was almost unbreakable. Manufacturing piston rings remains a cornerstone of the Cross business today.
The engine in GL1722 also features an aluminium liner-less barrel, special Cross piston and piston rings together with a four speed Burman foot-change gearbox. Performance was outstanding, with a compression ratio of 10.5 to 1 and running at 7,400 rpm speeds of 90 mph were easily achieved.
With the war looming large in 1938, GL1722 was parked up in a corner of the Cross workshop. It would sit there for almost 25 years, when young test rider and production engineer Cyril James begged the owner to ride it.
“My career with commenced in 1957 when I secured a position as a trainee production engineer,” said Cyril. “I was fortunate in that Mr Cross remembered my mum, who had worked for him at his house some years previously, and the interview was very limited indeed. On a beautiful, sunny Saturday morning Mr Cross asked me ‘So, you want to be an engineer?’ ‘Yes Sir’ I replied, to which he responded ‘I remember your Mum, will you be as hard a worker as she was?’ I said that I would and I started work on Monday 26th August 1957.”
Cyril, who now looks after GL1722, fell into his testing role by accident. As a rider of a 250cc Francis Barnett Cruiser 80, he gained the position by default when Des Cormack, the previous tester, left the company in 1959. After 30 months riding the Royal Enfield Crusaders they were developing, Cyril asked Roland Cross if he could ride the old HRD development bike.
“He told me ‘my son, if you can start it, you can ride it’. I did start it and I rode it. The bike was again put into storage, only being exhibited as a static display at various rallies or to support illustrated talks by Roland Cross.
“My career progressed and promotions at regular intervals saw me ascend to Head of Production in 1990. I had always retained my interest in the very special Cross engines and with the HRD/Cross 500cc rotary valve being such a special motorcycle, I firmly believed it should run again. Roland Cross had sadly passed away many years previously in 1970 and with his son Rodney now being Chairman, I discussed the possibility of restoring the HRD/Cross but it was clear that I could not be spared from my production management responsibilities.
“Just before my retirement, in 2006, a chap applied for a job and during the interview he revealed that he was a qualified motorcycle technician and in his spare time restored bikes. This chap was Chris Hawkings and I persuaded Rodney Cross to allow Chris the time to get GL1722 running again. We were very fortunate in that Des Cormack, although of mature years, was living only a few miles from Bath and I was in touch with him. Des was able to provide an amazing amount of advice and guidance to Chris and myself. So, in 2008 the HRD/Cross 500cc rotary valve was running again and I was able to ride it again, 47 years after I had last ridden it in 1961.”
Today Cyril continues to work with Cross on a part-time basis. In addition to looking after the very special Cross bikes and engines in the company’s in house museum, he continues to administer the company’s work experience scheme and regularly visits local schools and colleges to speak about mechanical engineering as a career.
He regularly rides GL1722 at rallies and events, while Cross remains a successful engineering consultancy company – working in partnership with leading aerospace and automotive companies and producing components including piston rings and turbocharger seals.