Billy (William M.) Davy – A 1920s Engineering Wizard?

In June 2009 we featured a piece about W.M. Davy from NZ converting a 2 3/4hp side valve Douglas engine into a OHC. The article came from a 1920s edition of the English motorcycling magazine The Motorcycle. Not much else was printed and so here endeth the story.

Well, Graeme from New Plymouth has passed on some more information and included some interesting photos of both the motorcycle and of Billy Davy.

Billy was from Hawera, and clearly from the outset he was going to be an achiever. Completing his apprenticeship as an electrician with Turnbull and Jones in Wellington qualifying by the age of 19 he was to join his relations firm, Hutchinsons Engineering Works, where his reputation and skills as a machinist were sort after by many from in the region. A keen radio enthusiast Billy was the first to receive an Australian broadcast at his home in Hawera. Treading the boards was another of Billys passions and he became a gifted entertainer, and loved drama taking part in stage productions. Sketching and doing impersonations added to the list of his talents.

Perhaps his love of engineering and invention contributed to his interest in developing what would prove to be quite a challenge, the desire to rebuild a 2 3/4hp Douglas twin to go fast. We will never know what convinced Billy to convert the Douglas to OHC but whatever it was the decision was made with the true belief that this could be the way of the future of performance.

The design of the horizontally opposed Douglas engine may have offered perfect balance, a good basic ingredient for any engine modifications but the lightweight construction of the 350 side valve Douglas crankshaft that could easily flex would have proven challenging. Added to that it seems that the total loss oiling system was still being used. Regulating the oil drips through the sight glass whilst racing around a sometimes dusty oval track would just be one of many issues that Billy would have had to overcome.

A man clearly with a desire to go fast Billy succeeded, with the Douglas winning many races on the bike throughout the North Island. Graeme is the current caretaker of Billys silverware, which includes the NZACU cup for Lightweight Championship, 6 Miles, 1918-19 Season, and a medallion from the NPMCC (New Plymouth Motorcycle Club) for the Taranaki Middleweight Handicap 05.03.21

A catalogue photograph of the original 350 side valve engine that powered the standard road going 2 3/4hp Douglas.

Billy and his Douglas with the first of many modifications. The original motorcycle was from about 1913 as it had the early type oil sight feed glass regulator. The v belt drive to the rear wheel has been changed to chain drive, Billy possibly realising that there would be less power loss from the little 350cc engine. The gearbox has been replaced by a countershaft.

A much cherished photo with creases indicating that it was folded and perhaps kept in a wallet. This is the much modified Douglas with rider.

A close up of the OHC engine and the drive chain. Billy made the barrels, new heads and camshafts.

Having achieved successes with the Douglas Billy moved on to a new project. This involved upgrading a JAP single cylinder engine to OHV. There are no details on the cycle equipment as to whether he made it as well but certainly a lot of thought went into it, including leaf spring front suspension.


The original drawing from Graeme outlining Billys own ideas on how he wanted to build his OHC JAP racer.


The completed racer and rider ready for some serious laps.


A closer view of Billys JAP OHC clearly showing his own cylinder head and barrel. The engines cylinder barrel and cylinder head have been through studded into the crankcase and the finning on the barrel would indicate that the engine is possibly using alcohol fuel.


A nice line up of racers from an event at Easter, 1919. 5 Harley Davidsons and one brave Douglas (with an even braver rider).


Billys contribution to the local motor racing industry was this race course score board that he built for the Hawera Race Course in 1925.


Riders getting ready for the start of a race, perhaps? Motorcycles that can be identified are – #24 Harley Davidson, a Norton in the middle somewhere, #25 Indian


Billy giving back, as a member of the Executive Committee for the Electricians Association, South Taranaki, 1935~1936.

Billy (William. M.) Davy passed away in October 1958, aged 70 years.

And as for his motorcycles, well hopefully somewhere in the corner of somebodies shed lies a couple of broken motorcycles waiting for their historical significance to be recognised. Such would be Billys legacy.

This is the original story from 2009.

Many thanks Graeme for sharing the story.

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