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.

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.

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.

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.

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] They were 20 lb (9.1 kg) lighter than the comparable 17 bhp (13 kW) cast-iron barrel and head B series single.

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.

[8][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.

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 [6] 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.

A small number of the early swingarm frames had a separate cast steel kink welded or brazed in place.

The engines maintained the same die-cast barrel and head with a separate rocker box design as with the late ZB models.

changed to 8 bolts, a stronger crankshaft, an even shorter connecting rod at 6+15⁄32 in (164 mm), oval flywheels (500),[12] improved valve gear with eccentric adjustment, and an Amal GP carburettor.

[citation needed] The DB Gold Star had an improved oil feed to the crankshaft and finned front brakes.

[14] The 500 cc DBD34 was introduced in 1956,[13] with clip-on handlebars, the same big finned alloy engine with a newly designed head,[8] 38 mm ( 1 1/2" ) bell-mouth Amal carburettor and swept-back exhaust.

Amongst the options available were a tachometer and a 190mm full-width front brake that gave a larger lining area than the standard 8" single-sided unit.

[19] Engine modifications included using a 350cc head, which had a better downdraught angle, machined to 500cc dimensions and fitted with a large inlet valve.

[8][21] Rigid framed machines became successful on the USA "Flat Track" scene in the hands of riders such as Dick Mann and tuners like CR Axtell.

[23] US West Coast BSA distributor, Hap Alzina, persuaded the factory to produce a replica named after the race.