BSA A10


THE HORSEPOWER RACE IS ON
The BSA A10 was the inevitable result of the relentless drive for more & more horsepower. Driven mostly by the performance-hungry US market (which also happened to be the largest by far), every British motorcycle maker scrambled to build a 500cc vertical twin after the war, in the mold of Edward Turner's game-changing 1938 Triumph Speed Twin.

THE A7 GIVES BIRTH TO THE A10
BSA Motorcycles followed suit with their own 500 twin, the BSA A7 in 1946. It was a fine machine and by 1950, it had proven itself to be sturdy & reliable. But, the pressure was on for more power, always more. Triumph had just punched their 500 twin out to a 650 in the 6T Thunderbird. BSA Motorcycles put their best men on it, Bert Hopwood & David Munro. Following British tradition, they started with the existing model, the 495cc BSA A7 as the template, then built off of that.

ALL NEW AND YET...THE SAME
Externally, the BSA A10 engine looked surprisingly similar to the BSA A7's engine & was laid out the same way, with one cam behind the cylinder block, driven off the right. And while they did, in fact, share some components in common, almost everything was different. They took the A7's 62mm bore & 82mm stroke & pushed them out to 70mm X 84mm for a new displacement of 646cc. The bore spacing was wider, so the crank was longer, so the crankcases were bigger & stronger. The one-piece forged steel crank benefited from BSA's advanced metals division as the rod journals were 'induction-hardened, ground & polished'. The A10 also got 2-piece lightweight alloy connecting rods made of RR56 aluminum.

A NEW HEAD
While the BSA A7 soldiered on with an iron cylinder head, the A10 got an all-new lightweight alloy head with a shallower valve angle, reworked finning for greater airflow & enhanced cooling & a single rocker box instead of two, as on the A7. This is probably the easiest & fastest way to differentiate the two. A BSA 500 A7 will have two rocker boxes & a BSA 650 A10 will have one big one.

NEW BRAKE, SAME OLD FRAMES
When the A10 debuted, it carried with it a new 8-inch SLS (Single Leading Shoe) front brake with a 1-3/8" wide hub made of Millenite (a high-grade iron alloy that again came from BSA's able metalworks). But the frames were the same as offered on the BSA A7. The new A10 could be ordered with either the older rigid frame or a plunger frame, until the new swingarm frame arrive in 1954.
ABOVE: 1958 650 BSA Golden Flash, an A10 model.

MODEL DESIGNATIONS
The first BSA A10 to be introduced in 1950 was the BSA 650 Golden Flash, & it ran through until replaced by unit construction in 1963. In 1953, BSA needed to hologate some production races, so they introduced the A10 Super Flash & killed it off in 1954, replacing it at that time with the hot new BSA Road Rocket which ran until 1957. From 1958 to 1963 BSA came out with the A10 Super Rocket complete with Amal TT racing carbs.

THE ULTIMATE A10
But the cream of the crop, the top dog, the big kahuna of not just all BSA A10's, but all BSA twins period, before or since, has to be the 1962-63 BSA Rocket Gold Star. This combined a tuned Super Rocket 650 twin engine with a single-cylinder BSA Gold Star frame, to get one of the fastest, best handling bikes of its day.
ABOVE: 1963 BSA A10 Rocket Gold Star

ANTI-CLIMAX
After helping write the book on vertical twins in the 1950's, BSA moved forward with plans to abandon it's popular pre-unit twins in favor of a whole new generation of 'modern' unit construction engines. The irony is that while these new engines certainly were better in many ways, they were never as popular as the older units they replaced & BSA began its slow slide to oblivion. The new unit construction BSA A65 650 twin & it's little brother that BSA A50 500 twin never sold in the kinds of numbers that BSA had become accustomed to in the late 1940s & throughout the 1950s.

BELOW: 1960 BSA A10 Spitfire Scrambler

BSA A10 YEAR-BY-YEAR


1951 BSA A10


1954 BSA A10


1957 BSA A10


1958 BSA A10


1959 BSA A10


1960 BSA A10


1962 BSA A10


1963 BSA A10



Check out these BSA BOOKS


HISTORY OF BSA MOTORCYCLES


GOLD STAR BUYERS COMPANION, 5th ED.


BSA PRE-UNIT TWINS


THE BSA GOLD STAR: MOTORCYCLE HISTORY


BSA PRE-UNIT TWINS


BSA MOTORCYCLES: THE FINAL EVOLUTION


BSA SINGLES RESTORATION, BY ROY BACON


BUILDING BUDGET BRITS: REFURBISHING BSA & TRIUMPH TWINS


BSA: ILLUSTRATED MOTORCYCLE LEGENDS BY ROY BACON


BSA UNIT SINGLES WORKSHOP MANUAL BY HAYNES


ILLUSTRATED HISTORY OF BSA MOTORCYCLES BY ROY BACON


BSA & TRIIUMPH TRIPLES: GOLD PORTFOLIO


BSA SINGLES 1964-1974 GOLD PORTFOLIO


BSA A50 & A65 TWINS 1962-1973 SHOP MANUAL BY HAYNES


BSA 500 & 650 TWINS: ESSENTIAL BUYER’S GUIDE


TUNE YOUR BEEZA BSA A10


BSA A7 & A10 TWINS, 1947-1962 SHOP MANUAL BY HAYNES


BSA UNIT SINGLES: THE COMPLETE STORY


BSA TWINS A50 & A65 GOLD PORTFOLIO


BOOK OF OHV & SV BSA SINGLES 1945-1954


BOOK OF OHV & SV BSA SINGLES 1954-1970


THE GOLD STAR BUYER’S COMPANION


BOOK OF THE BSA: SHOP MANUAL FOR PRE-WAR BSAs


BSA UNIT CONSTRUCTION SINGLES


MAINTENANCE MANUAL FOR THE BSA M20


HOW TO RESTORE YOUR BSA ROCKET III/TRIUMPH TRIDENT


BSA PRE-UNIT SINGLES SHOP MANUAL, 1954-1961 BY HAYNES


BSA TWINS A7 & A10 GOLD PORTFOLIO


BSA SINGLES 1945-1963 GOLD PORTOLIO


BSA TWIN RESTORATION BY ROY BACON


BSA UNIT TWINS


BSA BANTAM SHOP MANUAL, 1948-1971 BY HAYNES


BSA A50/A65 TWINS: ALL MODELS BY ROY BACON


BSA GOLD STAR & OTHER SINGLES BY ROY BACON


BSA BANTAM OWNERS MANUAL


BSA: CLASSIC MOTORCYCLES


CHILTON’S BSA MOTORCYCLE MAINTENANCE MANUAL


CLYMER’S SECOND BOOK OF BSA 500 & 650 TWINS, 1962-1969


RUPERT RATIO BSA UNIT SINGLE ENGINE MANUAL


BSA BANTAM BIBLE, 1948-1971


BSA BANTAM


BOOK OF THE BSA, ALL SINGLES & V-TWINS 1936-1952


BSA M20/21 SUPER PROFILE


BSA MOTORCYCLES 1935-1940


BSA ROCKET 3 & TRIUMPH TRIDENT 1968-1976 BY ROY BACON


BSA MOTORCYCLES SINCE 1950


BSA MOTORCYCLING ANNUAL 1937


1971-72 BSA 250-500 OWNERS MANUAL


1967 BSA BANTAM D1/D3/D5 OWNERS MANUAL


BSA TWINS & TRIPLES BY ROY BACON


HAYNES 1954-1961 BSA PRE-UNIT SINGLES SHOP MANUAL


BOOK OF BSA 500 & 650 TWINS 1948-1962 BY CLYMER


BSA: THE SCRAPBOOK SERIES


BSA BANTAM: THE ESSENTIAL BUYERS GUIDE


HAYNES 1947-1962 BSA A7 & A10 OWNERS SERVICE MANUAL BY HAYNES


BSA REPLACEMENT PARTS LIST 1971 BSA A75 ROCKET 3


BSA REPLACEMENT PARTS LIST 1968 BSA A75 ROCKET 3


BSA INSTRUCTION MANUAL: MODEL D10 BANTAM


BOOK OF THE BSA BANTAM


BSA GOLD STAR: PORTRAIT OF A MOTORCYCLING LEGEND


BSA COMPETITION HISTORY


BSA GOLD STAR SUPER PROFILE


HAYNES 1958-1972 BSA SINGLES OWNERS SERVICE MANUAL


TRIUMPH & BSA TRIPLES: THE COMPLETE STORY OF THE TRIDENT & ROCKET 3


BSA MOTORCYCLE CATALOG 1929


1949 BSA BROCHURE: WORLDS LARGEST MOTORCYCLE MANUFACTURER


BSA BANTAM, ALL MODELS BY ROY BACON


BSA GOLD STAR: MOTORCYCLE HISTORY


BSA PRE-UNIT SINGLES, B, C & M RANGES 1937-1963 BY ROY BACON


BSA UNIT SINGLES C15 TO B50, 1958-1973


BSA A7 & A10 TWINS, ALL MODELS 1946-1963 BY ROY BACON


BSA A50 & A65 TWINS, ALL MODELS 1962-1972 BY ROY BACON


ILLUSTRATED BSA BUYERS GUIDE BY ROY BACON


BSA FACTORY SERVICE SHEETS FOR THE 1950s


BSA BANTAM OWNERS POCKET BOOK


TRIUMPH TRIDENT & BSA ROCKET 3 SHOP MANUAL






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