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 BSA M24 HISTORY
On 30th June 1937, unknown to the higher echelons
of the company management, the competition department at BSA, managed by Bert Perrigo, entered a modified M23 500cc OHV Empire
Star machine in 2 races at a mid-week BMCRC meeting at Brooklands motor racing circuit. The bike was ridden by none other
than W.L. (Wal) Handley, who had been persuaded by his friend Perrigo to come out of motorcycle racing retirement for this
event. Handley had retired from motorcycle racing in 1935 after an illustrious career, which included a number of TT &
Ulster GP victories, and had opened a motor dealership in Birmingham as well as taking up 4 wheel racing & flying. He
and Bert Perrigo were both members of the Midland Aero Club.
Wal Handley and the 1937 Brooklands Empire Star
The bike was built by Len Crisp, and
the engine work done by Jack Amott, in the competition workshop at BSA. The engine , with a standard iron cylinder head and
barrel, was highly tuned, with a 13:1 high compression piston, special cams, a racing magneto, and ran on methanol fuel. Gear
ratios were altered to suit the Brooklands circuit. Power output was estimated at 34bhp. Handley started the first 3-lap race with a 9 second handicap,
and by the second lap had taken the lead. He went on to win the race by a huge margin, with an average speed of 102.27mph,
and averaged 107.57mph on his fastest lap. He was awarded a Brooklands Gold Star for achieving 100mph in the 500cc class.
In the next race, a two-lap affair, he again roared through the field after a handicap start, but on the second he collided
with another rider and crashed, fortunately without serious damage to himself. The Empire Star was damaged beyond repair.
Meanwhile,
BSA were developing an all-alloy 500cc single cylinder sports motorcycle, and it seemed only natural, in the wake of Handley’s
achievement, to call it the “Gold Star”.
Production of
the new machine started during the summer of 1937, and the first prototypes were ready in the autumn. One of these was used
for publicity photographs, and displayed at the Olympia Motorcycle show in November. There is no record
of how many pre-production bikes were made.
BSA publicity drawing of a pre-production M24 Gold Star
Pre-production M24 engine
1938 JM24 Gold Star
The first production bikes differed in certain
minor details from the prototype shown above. To overcome oil leakage problems, the cylinder head and barrel castings were
altered to incorporate two additional cylinder head fixing bolts on either side of the push rod tunnel, and the rocker box
was recast with two additional mounting bosses, again to overcome oil leaks. An Amal 10TT Carburettor was
fitted in place of the standard Amal type 76. The silencer on the production bikes had a separate tail
pipe, so that the overall length of the exhaust could be adjusted for optimum performance.
1937
BSA Engine brochure
Following the arrival at BSA
in 1936 of Val Page, the new range of motorcycles for 1937 revealed a significant redesign of the single cylinder engines,
with the adoption of dry sump lubrication. The all new M20 500cc side-valve engine, and the M19, M22 & M23 OHV engines
as pictured above, were to form the basis for all larger capacity BSA single cylinder engines until the final 500cc Gold
Star in 1962.
1938 BSA 500cc Empire Star
Based very closely on the
500cc M23 Empire Star, first produced for 1937, the 1938 production model Gold Star shared most of the older model’s
cycle parts, except the frame, which was constructed of lighter Reynolds 531 high-tensile tubing, the petrol tank, which was
unique to the Gold Star in having an integral tool box in the top, in place of the instrument panel, and the rear brake drum
which sported thin fins around its diameter. The ammeter and light switch were housed in a panel in the headlamp shell. The
other main visible differences were the all-alloy engine with built-in pushrod tunnel, the TT carburettor, and the “Elektron”
gearbox cases. The M24 also had a small tubular oil pressure indicator mounted above the timing case in place of an indicator
button in the tank top instrument panel of the M23. The
first production M24s , bearing Engine and Frame numbers starting at 101 and prefixed JM24, were built in
November/December 1937, and the first batch of 10 were dispatched on 17th December.
Production of 1938 Gold Stars continued
until the autumn of 1938, when the factory switched to production of the new 1939 model. The last one, engine JM24 365, in
frame JM24 404, was despatched on 6th July 1939 to the British Army for the 1939 ISDT.
A total of approximately
266 1938 JM24 bikes were built, and of these, 85 were despatched to destinations outside the UK.
1939 KM24 Gold Star
1939 BSA Catalogue drawing for 1939 Gold Star
1939 bikes carried the KM24 engine and frame number
prefix, again starting at 101.
Numerous
changes were made for 1939, including a new
petrol tank with tank-top instrument panel which housed
Lucas ammeter
& light switch, the oil pressure indicator
button and a Lucas mobile inspection light. A new shape
oil tank
was fitted, with the frame-mounted tool box below
and behind it. A short side-stand was added to the nearside
lower frame rail.
The 8in Lucas Headlamp reverted to a plain shell, a
valanced rear mudguard was fitted,
the exhaust
pipe profile became more angular and the silencer lost its
separate tail-pipe.
The magnesium gearbox
shell was dropped in favour of
aluminium alloy, and a close ratio gearbox was offered as
standard, with the option
of the wider ratios of 1938.
Minor external changes
were made to the cylinder head
and barrel pushrod tunnel, and the engine breather was
moved to the upper nearside
crankcase. Internally,
improvements were made to the timing gear and pushrods,
an additional ball bearing was
added on the timing side
of the crank shaft, and minor changes were made to the
carburation. Production continued until the outbreak of World War II
in September 1939, when BSA production
largely switched
to War Department orders for WD M20 military bikes. The
last KM24 bike made, KM24 422 was
despatched on 6/9/39
to the War Office. A total of 298 KM24 bikes were produced,
and of these,120 were despatched
to destinations outside
the UK.
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