The air cooled Lewis motor

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.

1903 Minerva as used in early Lewis motorcycles

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.

1904 Minerva engine, as used by Lewis

For 1904, Lewis used the 2 3/4 h.p. vertical Minerva motor.

c1906 Minerva motor in Lewis motorcycle

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.

1908 Lewis motor

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.

1909 Lewis motor

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.

1909 5-6hp Lewis twin cylinder

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?

1912 Lewis motor

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.

1914 Lewis motor

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.

Precision 499cc Type D.O. overhead valve

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.

1914 Lewis Precision twin

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.

ac1915twin.jpg (15526 bytes)

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 Precision offering.

c1915 JAP twin

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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