|The air cooled Lewis
Better known for their water-cooled
motors, Lewis offered air-cooled models in each of its production years. Prior to
1903, Lewis experimented with a range of power units, including their own (O'Grady's
engine in the Lewis motor triplet),
Kelecom, MMC and early clip-on Minervas. The power units listed below, all sourced from
established makers, cover the majority of air-cooled Lewis output.
||When Lewis settled into "routine"
motorcycle production around 1903, they did so with the 2 h.p. Minerva unit that was used
so successfully by hundreds of manufacturers world wide. For 1903 it featured fully
mechanical valves (previously the inlet valve was atmospheric) and a spray carburettor.
Vivian Lewis, Alf. Lykke and Norman Jackson rode Lewis machines powered by this motor at
the Opening Run of the Automobile Club of
South Australia in November 1903.
||For 1904, Lewis used the 2 3/4 h.p. vertical
||Lewis used the magneto-ignition 2 3/4 h.p.
Minerva motor for the bulk of its output in 1905-06. The magneto here is a low-tension
Eisemann, which was driven by an eccentric coupling rather than the usual chain or gears.
The magneto fed a high tension coil housed in a compartment in the fuel tank. The sleeve
that couples the exhaust pipe to the port was characteristic of this period, but is
unknown on Minervas used elsewhere. The Minerva motor may have been used by Lewis as late
as early 1908. At least one Lewis used a 4 1/2 h.p. Minerva V twin.
||The first of the Lewis-branded side-valve motors
appeared in water-cooled form 1907, but the earliest reference I have to the air-cooled
version of the 3 h.p. motor is in March 1908 when it was described as a "distinct
novelty". This illustration is from the 1909
catalogue. This motor was sourced from the Stevens Motor
Manufacturing Co., Ltd. in Wolverhampton. A key identifier is the somewhat
heart-shaped timing chest, whose cover was bronze on the earliest models, but later became
aluminium. One survivor has a cast-iron timing cover. Production ran into 1910.
||The 3 1/2 h.p. motor used by Lewis in 1909-1910
is the same as used in the contemporary ROC motorcycle, built by A.W.
Wall Ltd. in Birmingham. It is not known whether Wall built the motor themselves, or
sourced it from elsewhere. In detail it is a little more sophisticated than the 3 h.p.
Stevens motor, but it was used only for a short period and was discontinued when Precision
motors became available. The engine numbers on these motors are in the same sequence as
the 3 h.p. motors, and are interlaced in the period when both motors were offered.
||This is the 5-6 h.p. Lewis twin from the 1909 catalogue. There are some obvious
similarities with the 3 1/2 h.p. motor from the same catalogue (particularly in the timing
chest and tappet layout, magneto drive from the rear cam, and in the cylinder finning) so
it comes as no surprise that the same motor was offered in a ROC
motorcycle. Unlike the 3 1/2 single, the twin motor seems to feature bolt-on exhaust
ports. Is there a survivor?
||From late 1910, Lewis began sourcing motors from
F.E. Baker in Birmingham. The Precision motor as used by Lewis was offered in two
sizes: 3 h.p. and 3 1/2 h.p. This is the larger of the two, 85 x 88 mm giving 499 cc,
recognisable by the relatively wide spacing of the valves. The illustration is from the 1914 Lewis catalogue, but shows a
1912-pattern motor. The barrel on the Lewis motor differed from the catalogued Precision
item: the latter was "square" in shape, with the exhaust port angled further
forward than the Lewis item. The Precision brand was not used on any Lewis motor from
Baker, possibly to avoid problems with the local Precision distributor.
||Changes were relatively minor over the 5 year
lifespan of the Lewis Precision motor. On the 1914 pattern motor, the only noticeable
departure was the rounded bottom to the timing gear case. Engine numbers on these later
Lewis motors fit in with the standard Precision sequence.
||Around 1913-14, Lewis built a small number of
overhead valve machines for racing and competition work, based on the Precision 499cc Type
D.O. motor. As for the side valve engines, the timing covers and magneto chain cases of
these machines had the Lewis name cast in, but were otherwise identical with the Precision
item shown here from an undated catalogue, c1914.
||The 6 h.p. Precision twin, shown here from the 1914 catalogue, was used around
1914-15. Unlike the singles, the twin seems identical in specification to the catalogued
Precision item, except that the Lewis engine does not carry the Precision brand, which was
cast on the standard Precision crank case.
||The 4 h.p. twin was a late inclusion in the 1914 catalogue: registration records
show it appearing in very small numbers in 1915-16. Again the motor is a standard
||The 6 h.p. JAP twin, and later its almost
identical 8 h.p. big brother, was used by Lewis from around 1916 through into the early
1920s. The JAP engine was almost always coupled with a three-speed gearbox with
chain-and-belt transmission. It is possible that the smaller 5 h.p. JAP was also used, on
occasion, in the mid teens.
||A new model for 1920 used the 3 1/2 h.p. (350
cc) Precision two stroke.
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