BSA M24 HISTORYOn 30th June 1937
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.
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”.
Wal Handley and the 1937 Brooklands Empire Star
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 pre-production publicity
for the new Gold Star
Pre-production M24 engine 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.
1938 JM24 Gold Star
BSA Engine brochure
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
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.
of approximately 266 1938 JM24 bikes were built, and of these, 85 were despatched to destinations outside the
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.
changes were made for 1939, including a new
petrol tank with tank-top instrument panel which housed
& light switch, the oil pressure indicator
button and a Lucas mobile inspection light. A new shape
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,
pipe profile became more angular and the silencer lost its
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
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
Production continued until the outbreak of World War II
in September 1939, when BSA production
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