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BSA B25
The BSA B25 was a series of 250 cc (15 cu in) unit construction single-cylinder OHV four-stroke motorcycles made by the Birmingham Small Arms Company. Developed from the BSA C15, the machines were produced between 1967 and 1971. The B25 was the fastest British production 250.
The 247 cc engine was a higher performance development of that used the existing C15. Bore and stroke of 67 x 70 mm was retained, but a new alloy barrel and cylinder head were introduced featuring square fins. The pushrod tunnel was cast into the barrel rather than being a separate item as on earlier models. Tappet adjustment was by eccentric rocker shaft.
To improve performance the inlet tract was opened up and bigger valves fitted along with the newly introduced Amal Concentric carburettor. Compression ratio was increased to 10:1 and a sports camshaft used. Power output was 26 bhp (19 kW) at 7250 rpm, (later reduced to 22.5 bhp (16.8 kW) on the P34 models) The engine was free-revving and would rev to over 8,000 rpm.
Unlike the later C15s, which used a roller bearing big end, the B25 reverted to a plain big end and split conrod. The model gained a reputation for unreliability due to big end and conrod failures. BSA attempted to address this in the P34 models by fitting a conrod with a larger shoulder. The oil pump was also changed to a cast iron body design, the earlier zinc alloy bodies tending to distort and reduce oil pressure. An inline paper oil filter was also added to improve oil quality.
A duplex chain took power to a wet, multi-plate clutch. The gearbox had 4 speeds and final drive was by chain.
Developed from the competition C15s, the all-welded frame had a single downtube that split into two to form a cradle under the engine. The later P34 used a frame where the oil was stored in the top spine, this frame was shared with the B50 models.
Electrics were upgraded to 12v (the C15 used a 6v system). The output from the alternator was regulated by a zener diode with a large heat sink mounted between the front forks.
The first model of the series was introduced in 1967 as the C25 Barracuda in the UK and the B25 Starfire in the USA (although the US models had frame and engine numbers prefixed C25). The model was a more sporty replacement for the C15 and, in the UK, aimed at learner riders.
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BSA B25 AI simulator
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BSA B25
The BSA B25 was a series of 250 cc (15 cu in) unit construction single-cylinder OHV four-stroke motorcycles made by the Birmingham Small Arms Company. Developed from the BSA C15, the machines were produced between 1967 and 1971. The B25 was the fastest British production 250.
The 247 cc engine was a higher performance development of that used the existing C15. Bore and stroke of 67 x 70 mm was retained, but a new alloy barrel and cylinder head were introduced featuring square fins. The pushrod tunnel was cast into the barrel rather than being a separate item as on earlier models. Tappet adjustment was by eccentric rocker shaft.
To improve performance the inlet tract was opened up and bigger valves fitted along with the newly introduced Amal Concentric carburettor. Compression ratio was increased to 10:1 and a sports camshaft used. Power output was 26 bhp (19 kW) at 7250 rpm, (later reduced to 22.5 bhp (16.8 kW) on the P34 models) The engine was free-revving and would rev to over 8,000 rpm.
Unlike the later C15s, which used a roller bearing big end, the B25 reverted to a plain big end and split conrod. The model gained a reputation for unreliability due to big end and conrod failures. BSA attempted to address this in the P34 models by fitting a conrod with a larger shoulder. The oil pump was also changed to a cast iron body design, the earlier zinc alloy bodies tending to distort and reduce oil pressure. An inline paper oil filter was also added to improve oil quality.
A duplex chain took power to a wet, multi-plate clutch. The gearbox had 4 speeds and final drive was by chain.
Developed from the competition C15s, the all-welded frame had a single downtube that split into two to form a cradle under the engine. The later P34 used a frame where the oil was stored in the top spine, this frame was shared with the B50 models.
Electrics were upgraded to 12v (the C15 used a 6v system). The output from the alternator was regulated by a zener diode with a large heat sink mounted between the front forks.
The first model of the series was introduced in 1967 as the C25 Barracuda in the UK and the B25 Starfire in the USA (although the US models had frame and engine numbers prefixed C25). The model was a more sporty replacement for the C15 and, in the UK, aimed at learner riders.