In 1916, neither V twin motors nor multi-speed gears were new to Lewis. In fact both had entered the Lewis model line-up around 1905-6, when at least one machine was fitted with a V twin Minerva motor, and the NSU two-speed epicyclic gearbox, fitted to the engine shaft and operated by a coffee-grinder handle at the top tank rail, became a common fitment to machines across the Lewis range. In following years, new V twin motors came from A. W. Wall (1909) and F. E. Baker (late 1912), and alternate transmissions from Endrick (two speeds, mounted at the pedal bracket), and Armstrong (and possibly Sturmey Archer) who offered three speeds, bicycle style, inside the rear hub.
In early 1916 the "standard low-built Lewis" was little changed from the 1914 catalogue illustration below. The 6 h.p. motor was effectively the proprietary Precision except that the crankcases did not carry the Precision name. Lewis never hid the fact that their motors were made in England (a badge of honour at the time), but they always referred to is as the "Lewis motor".
If a customer wanted a clutch and gears - essential for sidecar service - he had the choice of the NSU two-speed pulley or an Armstrong three-speed hub. In March 1916, Lewis paraded an entirely new model before the crowd at the Angaston Show, featuring at last a countershaft gear box (the well known Sturmey Archer CS, as used on thousands of Triumph machines from late 1914) with chain-cum-belt transmission. Although we have no illustration of this model, there is a survivor which was registered in April 1917 and remains to this day in the same family. The motor was a 6 h.p. "Lewis" (Precision), and the frame was one built almost entirely of Chater Lea lugs, including the Chater Lea front fork which was little changed since its first use by Lewis in 1910.
Manufacturing motorcycles in war-time Australia using British components was not easy, and in April 1917, a year after the introduction of the Lewis 6 h.p. Countershaft Model, the Precision motor was replaced by a JAP of the same nominal horse power. The 6 h.p. Lewis JAP, shown below from an undated but c. April 1917 single sheet brochure, is essentially identical to the surviving Precision-engined bike.
A common feature of the Precision and JAP countershaft Lewis twins was the use of Chater Lea fittings and forks and "a special bracket fitted to the frame to carry the countershaft gear, so arranged as to give plenty of ground clearance for [the] gearbox". This clever but slightly crude "bracket" is distinctly different from the usual lug used by Australian manufacturers to mount the Sturmey Archer gear box. It mounts neatly between the standard Chater Lea rear engine mount and back fork lugs which are usually joined by a large diameter tube. Two additional attachment points accept the saddle tube, and a bracing tube which arches over the gear box platform. Note that the lug joining the arch and the saddle tube appears identical to that used to attach the the lower tank directly above it. The crudeness of the finish on the lug and its uniqueness to Lewis frames (has anyone seen it elsewhere?) suggest local manufacture. In the absence of knowledge of the true inventor, I propose we attribute the design to Tom O'Grady, Vivian Lewis' "motor expert" and 25-year "right hand man". Sadly Tom died in September 1916, six months after the distinctive lug was used for the first time.
As the war continued, supply of British components all but dried up, and between September 1917 (only six months after the announcement of the Lewis JAP) and October 1919 no evidence has been found for manufacture of the 6 h.p. twin. If any were built in this period the number was likely very small indeed. In September 1919 Lewis announced that they were "Booking New Orders for The Famous 6 h.p. Lewis JAP twin cylinder, with 3-speed gear box and kick starter". Although they claimed that these "are entirely new models and [they] embody all the very latest improvements", the model on display at the Autumn Show in March 1920 sounded awfully like a 1917 model: "The fittings used throughout in the manufacture of the frames are the well-known Chater Lea, including their magnificent patent spring forks". Perhaps it was simply the shortage of motors - and not lugs - that halted production of Lewis twins.
Beware, then, when trying to date the Lewis JAP motorcycle. From existing evidence it seems likely that those built in March-September 1917 and those built in September 1919-March 1920 may have been very similar indeed. Adding to the problem is that, as part of the post-war export drive, 1917 and 1918 JAP engines - some stamped "WAR PRODUCT" - were sent out to Australia and fitted into new Australian-built machines in 1919 and 1920. What could be more problematic with the Australian cut-off date for the "veteran" era set at 31 December 1918?
The Lewis JAP did live on beyond the supply of Chater Lea lugs, and was built in the period 1920 - 1922 using other lug sets and the almost-universal Druid front fork.