The most commonly mentioned Air Cleaner is the "Vokes" filter
(refering to the manufacturer). There were however more designs.
The first filters found on 30 ties type Norton
motorcycles are seen on bikes destined for Palestine and India . These
bikes show a biscuit tin like round box, mounted at the right hand
side of the rear wheel. The wheel itself is valanced with a sheet of
metal, most likely mounted in the same way as later seen on the
lefthand front side of the Big 4 combinations. The valance obviously
serves as a shield to deflect stones and dirt in general from reaching the
filter. This filter is described in 1936 spare parts list
(contract C8753) with Norton numbers. The Cleaner was
described in the Norton Assembly books as "Vokes C1a Protectomotor Air
Cleaner", so it was obviously made by Vokes.
Left: 1936 16H most likely destined for Palestinenad or India, likely from
Contract C8753. Right: Bernhard Hope in 1942 after Alamein. The bike still sports the
tubular Air Cleaner first seen in 1936! Was this one of
those bikes destined for Palestine?
Only the speedometer is additional to the pictures of 1936.
"He was riding East to
Barrani from Tobruk, Libya, and he was doing at least 60 hence his
ANZAC slouch hat hanging round his neck" (remark from the
Picture left: Possibly a picture from a bike as proposed for an "India" contract. It shows the 1938 engine (no oil tell tale), upswept
silencer, large crankcase shield, front mudguard stays with lifting
handle, pillion seat, saddle with knee padding and lugage carier, all given in
a 1939 spare parts list (Government of India contract Y6730/8279). Contrary to that
spare parts list however, it still shows the earlier round dust
Picture right: A tank top Vokes Air Cleaner on a pre/early wartime
production machine, also sporting a petrol tank with the rear end
cut-off to facilitate the hose. It seems that this is not a machine as initially
described as India machines. The picture came from Australia, but
the provider could not tell much about it. It has the oil tell tale indicating
it to be the 1937 spec engine. It shows to have a fixed, one
piece, elbow, contrary to the later types using an
adjustable 3 piece elbow. The bike
itself is as made upto October 1940.
The first mention of a "Vokes Air cleaner, modified" is found on
15th of November 1937 in relation to bikes for the Nizam Forces in
India. Athough there is no description of the filter, the addition
of "Modified" may be referring to the Vokes Tank top
filters. An even likely explanation of "modified" could be the C1a
denomination of the biscuit tin Air Cleaner. Norton had the habit
of identifying modified parts with a suffix "a". No mention of a modified petrol
tank as well in 1937. The first rather certain indication for the
Tank Top mounted Vokes is seen on
pictures of a prototype Big4 machine (Military reg C385695) of
1938 which is clearly provided one (below, left hand picture). It
also shows the right rear end of the tank being cut-off, and fixed
non adjustable straps to the kneegrip screws and non adjustable
elbow to Carburetter. The right hand picture shows the Air
Cleaner mounted on a later 16H bike with adjustable fixing straps
The spare parts list of the Norton Contract S5161 shows a VAOS
(Vocabulary of Army Ordnance Stores) parts number MT12/NC/11783 for
the Air Cleaner complete.
Within the VAOS spareparts system, part numbers with NC are Norton
spare part numbers. Even the Airfilters described in a Arial WN/G
spare parts list refer to these same VAOS numbers (as also shown in the
latest book of O&M).
The consistent reference to Norton suggests a
strong link between the design and Norton. As Vokes was a renowned air filter manufacturer,
it is most likely that they either did (participate in) the design for
Norton, or the Norton design was taken over as is, in the end becoming the
"Universal Air Cleaner".