Veteran motorcycles with overhead valves are rather rare, but it seems that a number of Australian-assembled motorcycles used ohv Precision motors. My c1913 Bullock - a product of the Bullock Cycle Works in Adelaide - uses the 2 3/4 hp version in pure Sun cycle parts. The machine was discovered in the Milang area in the 1960s, where it had reputedly been once owned by the local police sergeant.
Viewed against its big brothers - the 500cc ohv Precision in air-cooled or water-cooled Green-Precision form - the 2 3/4 is tiny, scaled down substantially in all features. The magneto chain cover has Bullock cast into it, together with the brass Precision badge rivetted on, suggesting that it left the Precision factory in the UK in that form. My best guess is that Bullock ordered the sporty ohv motor specially from F.E. Baker at the Precision Works - for themselves or a customer - and fitted it to Sun cycle parts that probably started life with the side-valve version of the same motor. The bronze engine plates look decidedly hand crafted, but also sufficiently battle scarred to be sure that they have had a long life in the machine. Another tell-tale sign of long association between the motor and cycle parts is wear on the underside of the frame tank rail where poorly adjusted rockers have left their mark.
It must be said that the Bullock has had a somewhat difficult re-birth. I restored the bike 4 years ago, but having expended an enormous amount of effort, I've not been able to get it to run properly. Very disappointing. There are two things that have me deeply worried: the very high compression ratio (6.7:1, which seems inappropriate for a veteran motorcycle, even a sporty one) and the outrageous valve timing (where the exhaust valve stays open for 300 degrees).
The bike has been sitting at the back of the shed in disgrace for a couple of years. I guess it is nearly time to drag it out again and see what can be done.