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BSA Gold Star
The BSA Gold Star is a motorcycle made by BSA from 1938 to 1963. They were 350 cc and 500 cc single-cylinder four-stroke production motorcycles known for being among the fastest bikes of the 1950s. Being hand-built and with many optional performance modifications available, each motorcycle came from the factory with documented dynamometer test results, allowing the new owner to see the horsepower (bhp) produced.
The Gold Star was almost continuously developed over its lifetime by BSA's engineers and riders, who improved its capabilities and increased output from its essentially simple push-rod petrol engine beyond what had been thought possible[by whom?]. It was highly successful across almost all areas of motorcycle sport for well over a decade and is widely regarded by enthusiasts as a notable design of its era.
In 1937, Wal Handley lapped the Brooklands circuit at over 100 mph (160 km/h) on a BSA Empire Star and was awarded one of the traditional Gold Star badges. That inspired BSA to produce the BSA Gold Star. The first Gold Star was an M24 model. It had an all-alloy 82 mm × 94 mm (3.2 in × 3.7 in) bore and stroke, 496 cc (30.3 cu in) displacement, with a separate rocker box, bolted to the aluminium head, pushrod valve actuation, an Elektron (magnesium alloy) gearbox with close ratio option, and a rigid frame and girder forks made of Reynolds 531 light tubes devoid of sidecar attachment lugs. This model continued up to the start of World War II.
There were two variants of the M24; 1938, JM24 and 1939, KM24. Both had a capacity of 496cc Several modifications were made to the design during its lifespan. The 1939 KM model used a redesigned crank and crankcase with timing gears on fixed shafts, supported by a strong steel "outrigger" plate (a feature carried on throughout the Gold Star's entire production period.) The earlier JM model had cams that ran directly in the timing cover, with the potential for premature wear, hence the re-design. Power outputs were around 30bhp. The cast Elektron gearbox was dropped in 1939 to use the side-valve M20's cast aluminum shell but with close gear ratios as an option. Some KMs were used by the military at the start of WW2. 266 JM24 models were produced and 298 KM24, of which 120 were sent to destinations outside the UK. There are over 100 recorded survivors on the bsa-m24.com website
After the war, in 1945–46, BSA introduced the iron engine 348 cc (21.2 cu in) B31 and subsequent 499 cc (30.5 cu in) B33. In preparation for the 1949 model season, and to attract sporting buyers, the 71 mm × 88 mm (2.8 in × 3.5 in) bore and stroke, all alloy 348 cc ZB32 type Gold Star was first shown at the Earls Court motorcycle show at the end of 1948, with an extensive list of optional components. Unlike the pre-war M24 engine, the cylinder head was a strong one-piece casting, with the rockers incorporated into the unit. The all-new spring frame had so-called plunger suspension, halfway between the earlier rigid and later swingarm types. These used undamped springs mounted on shafts and forgings on either side of the rear wheel spindle and although they offered more comfort for regular road riding compared to rigid frames, they came in time to be regarded by competition riders and racers as often criticized by competition riders as heavy and difficult to handle.[citation needed] Once ordered the bike was assembled by hand, and the engine bench tested and not released unless an acceptable power output was achieved,[citation needed] which was around 25 bhp (19 kW), depending on specification.[citation needed] They were 20 lb (9.1 kg) lighter than the comparable 17 bhp (13 kW) cast-iron barrel and head B series single. They were almost immediately successful, winning the Manx Grand Prix Clubmans 350 class from 1949 and remained so until 1956 when the class was discontinued. They could be specified in tourer, trials, ISDT, scrambles, racing or Clubman trim. Racing models used the well-established[opinion] Amal TT carburettor.
The rest of the 1948 BSA OHV B range "YB" models in the standard and competition forms had heavy but reliable[opinion] cast iron heads and barrels. BSA reportedly experimented with new prototype components.[citation needed] It has been suggested[by whom?] that a very small number of YB32 competition engines may have had aluminum ZB32-type barrels and heads. These would have been "works" prototype bikes rather than true production Gold Stars.[citation needed]
In BSA's model numbering system, Y denotes the year and B the range, followed by the engine number; YB is 1948, ZB is 1949, and so on, except that some models were available for more than one year so the number remained the same over that time.[better source needed] All genuine[peacock prose] bench-tested Gold Stars had the addition of "GS" after the year and range letters; thus ZB32GS, followed by the actual engine number. A standard YB32 or subsequent years competition machine was not a Gold Star as it did not have a bench-tested engine or the full "GS" engine number. In subsequent years BSA produced competition machines delineated with a stamped "A" to signify an aluminium engine. They were not bench-tested Gold Star engines, despite the physical similarities and use of some of the same parts.
In 1949 the B32 Gold Star was in full production. The 499 cc B34 Gold Star was introduced, with a modified heavier crankshaft, stronger drive side crankcase, larger diameter drive-side main shaft, and a different design main bearing. The 350 cc continued as before. Spring plunger frames were most commonly used, along with a standard B-type rigid option for trial competition use. In 1950 both received larger 8" front brakes. In late 1951 the 500 gained a new barrel and Bert Hopwood design head with a separate rocker box, and the 350 had a new barrel and head of that design the following year The earlier 7+3⁄8 in (190 mm) connecting rod was shortened by 1⁄2 in (13 mm), which with other improvements gave an increase in power beneficial for performance. This engine redesign initially used sand-cast heads and barrels, still designated as ZB. After engine number ZB32GS-6001 production moved to die castings which allowed a more accurate and cleaner finish.
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BSA Gold Star
The BSA Gold Star is a motorcycle made by BSA from 1938 to 1963. They were 350 cc and 500 cc single-cylinder four-stroke production motorcycles known for being among the fastest bikes of the 1950s. Being hand-built and with many optional performance modifications available, each motorcycle came from the factory with documented dynamometer test results, allowing the new owner to see the horsepower (bhp) produced.
The Gold Star was almost continuously developed over its lifetime by BSA's engineers and riders, who improved its capabilities and increased output from its essentially simple push-rod petrol engine beyond what had been thought possible[by whom?]. It was highly successful across almost all areas of motorcycle sport for well over a decade and is widely regarded by enthusiasts as a notable design of its era.
In 1937, Wal Handley lapped the Brooklands circuit at over 100 mph (160 km/h) on a BSA Empire Star and was awarded one of the traditional Gold Star badges. That inspired BSA to produce the BSA Gold Star. The first Gold Star was an M24 model. It had an all-alloy 82 mm × 94 mm (3.2 in × 3.7 in) bore and stroke, 496 cc (30.3 cu in) displacement, with a separate rocker box, bolted to the aluminium head, pushrod valve actuation, an Elektron (magnesium alloy) gearbox with close ratio option, and a rigid frame and girder forks made of Reynolds 531 light tubes devoid of sidecar attachment lugs. This model continued up to the start of World War II.
There were two variants of the M24; 1938, JM24 and 1939, KM24. Both had a capacity of 496cc Several modifications were made to the design during its lifespan. The 1939 KM model used a redesigned crank and crankcase with timing gears on fixed shafts, supported by a strong steel "outrigger" plate (a feature carried on throughout the Gold Star's entire production period.) The earlier JM model had cams that ran directly in the timing cover, with the potential for premature wear, hence the re-design. Power outputs were around 30bhp. The cast Elektron gearbox was dropped in 1939 to use the side-valve M20's cast aluminum shell but with close gear ratios as an option. Some KMs were used by the military at the start of WW2. 266 JM24 models were produced and 298 KM24, of which 120 were sent to destinations outside the UK. There are over 100 recorded survivors on the bsa-m24.com website
After the war, in 1945–46, BSA introduced the iron engine 348 cc (21.2 cu in) B31 and subsequent 499 cc (30.5 cu in) B33. In preparation for the 1949 model season, and to attract sporting buyers, the 71 mm × 88 mm (2.8 in × 3.5 in) bore and stroke, all alloy 348 cc ZB32 type Gold Star was first shown at the Earls Court motorcycle show at the end of 1948, with an extensive list of optional components. Unlike the pre-war M24 engine, the cylinder head was a strong one-piece casting, with the rockers incorporated into the unit. The all-new spring frame had so-called plunger suspension, halfway between the earlier rigid and later swingarm types. These used undamped springs mounted on shafts and forgings on either side of the rear wheel spindle and although they offered more comfort for regular road riding compared to rigid frames, they came in time to be regarded by competition riders and racers as often criticized by competition riders as heavy and difficult to handle.[citation needed] Once ordered the bike was assembled by hand, and the engine bench tested and not released unless an acceptable power output was achieved,[citation needed] which was around 25 bhp (19 kW), depending on specification.[citation needed] They were 20 lb (9.1 kg) lighter than the comparable 17 bhp (13 kW) cast-iron barrel and head B series single. They were almost immediately successful, winning the Manx Grand Prix Clubmans 350 class from 1949 and remained so until 1956 when the class was discontinued. They could be specified in tourer, trials, ISDT, scrambles, racing or Clubman trim. Racing models used the well-established[opinion] Amal TT carburettor.
The rest of the 1948 BSA OHV B range "YB" models in the standard and competition forms had heavy but reliable[opinion] cast iron heads and barrels. BSA reportedly experimented with new prototype components.[citation needed] It has been suggested[by whom?] that a very small number of YB32 competition engines may have had aluminum ZB32-type barrels and heads. These would have been "works" prototype bikes rather than true production Gold Stars.[citation needed]
In BSA's model numbering system, Y denotes the year and B the range, followed by the engine number; YB is 1948, ZB is 1949, and so on, except that some models were available for more than one year so the number remained the same over that time.[better source needed] All genuine[peacock prose] bench-tested Gold Stars had the addition of "GS" after the year and range letters; thus ZB32GS, followed by the actual engine number. A standard YB32 or subsequent years competition machine was not a Gold Star as it did not have a bench-tested engine or the full "GS" engine number. In subsequent years BSA produced competition machines delineated with a stamped "A" to signify an aluminium engine. They were not bench-tested Gold Star engines, despite the physical similarities and use of some of the same parts.
In 1949 the B32 Gold Star was in full production. The 499 cc B34 Gold Star was introduced, with a modified heavier crankshaft, stronger drive side crankcase, larger diameter drive-side main shaft, and a different design main bearing. The 350 cc continued as before. Spring plunger frames were most commonly used, along with a standard B-type rigid option for trial competition use. In 1950 both received larger 8" front brakes. In late 1951 the 500 gained a new barrel and Bert Hopwood design head with a separate rocker box, and the 350 had a new barrel and head of that design the following year The earlier 7+3⁄8 in (190 mm) connecting rod was shortened by 1⁄2 in (13 mm), which with other improvements gave an increase in power beneficial for performance. This engine redesign initially used sand-cast heads and barrels, still designated as ZB. After engine number ZB32GS-6001 production moved to die castings which allowed a more accurate and cleaner finish.
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