BSA A50 Royal Star

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The BSA Royal Star, also called the A50 Star or Star Twin, was a 498cc twin made by Birmingham Small Arms (BSA) from 1962 to 1970. It followed the A7 and fed a growing market with a robust, easy-to-handle motorcycle. The bike used unit construction, with the engine and gearbox cast as one piece, which reduced oil leaks and gave a cleaner engine look. This change came as Lucas switched motorcycle electrics from magnetos to alternators, prompting a move to full unit construction.

Launched in 1962 as the 500cc BSA A50 Star, it was exported mainly to the US and Australia and sold well in the UK. In export markets it was known as the Royal Star; in the UK it was called the Star or Star Twin. From 1966 onward, the Royal Star name was used in all markets. It shared many parts with the larger A65 Star 650 twin and was built to be durable, even in busy touring use.

Key specs
- Engine: 498cc air-cooled twin
- Power: about 33 bhp at 5800 rpm
- Transmission: four-speed gearbox driving a chain
- Wheelbase: 54.75 in (139 cm)
- Length x width: 81 in x 11.7 in (approx. 210 cm x 30 cm)
- Seat height: 32 in (81 cm)
- Weight: about 392 lb (dry)
- Fuel capacity: 4 gallons

Design and performance
- The Royal Star used a small 1" Amal Monobloc carburetor early on, later upgraded to a Concentric carb.
- In 1964, pistons were updated to 8.5:1 and the gearbox was improved for better performance.
- Top speed was around 90 mph, and the bike stayed relatively smooth with low vibration.
- A common early fault was a plain crankshaft bearing on the timing side that could wear and lower oil pressure. In 1965, BSA addressed this with a drive-side roller bearing and a bronze timing-side bushing.

Cyclone variants
- The Cyclone was the higher-performance version of the same basic bike.
- A50 Cyclone Competition (1964, US): dual 1 1/16" carburetors, 10.5:1 compression, magneto ignition, larger front brake, 2-gallon fuel tank, upswept exhaust, no road lights.
- A50C Cyclone Road (1964–65): dual carburetors, 9:1 compression, battery ignition, larger front brake, 2-gallon tank, road lights.
- UK market versions offered 9:1 compression, battery ignition, and 4-gallon tanks.

Overall, the Royal Star was a sturdy, well-engineered bike that helped establish BSA’s unit-construction twins and found popularity in both the UK and overseas markets.