Triumph Thruxton Bonneville

Years produced: 1965 - ?
Total production: 52
Claimed power: 54bhp @ 6,500rpm
Top speed: 140+mph
Engine type: Overhead valve, air-cooled, vertical twin 
Weight (dry): 157kg (350b)  
Price then: $925 (est.)
Price now: If you have to ask ...

2005 Triumph Thruxton 900

Years produced: 2004-present
Total production: N/A
Claimed power: 69bhp @ 7,250rpm
Top speed: 110mph
Engine type: Dual overhead cam, air-cooled, vertical twin 
Weight (dry): 205kg (451lb)
Price now: $7,999

BSA produced just 1,584 Rocket Gold Stars, the iconic pairing of Gold Star cycle parts and 650cc Super Rocket engines. It’s said that only about 2,000 still exist.

Those numbers don’t jibe, of course, and that’s because any time a factory assembles a special motorcycle using over-the-counter parts, unscrupulous shade-tree mechanics will try to make a fast buck by putting together their own. Such is the case with the Triumph Thruxton Bonneville — a bike that propelled Triumph to the winner's circle during the 1960s and inspired the modern Triumph café racer, the Triumph Thruxton 900. Early Thruxtons were created not only by private individuals but by Triumph dealers — at the company’s encouragement. But what is a real Thruxton?

In May 1965, the Triumph factory in Meriden, England, produced 52 tuned Thruxton Bonnies to homologate the type for production racing. It’s known that the 52 came from a batch numbered from DU23129 to DU23181, but other production machines were later diverted for Thruxtonization. And many dealers built Thruxtons from factory tuning parts.

Hints of greatness

Okay, let’s get this out of the way up front: Owner David Haydon can’t be certain whether his 1969-registered Thruxton Bonneville is a genuine factory racer or merely a collection of factory tuning parts fitted by a dealer to a stock Bonnie. But there are several clues that this is a special bike.

Read David Haydon's review of owning and riding a 1969 Triumph Thruxton Bonneville 

When Haydon bought it, the engine was fitted with high-compression, 11:1 pistons — not really suitable for the street. In the valve train, Haydon discovered Triumph competition shop exhaust cam followers, specially designed with a larger radius to not only reduce friction loads on the cam lobes (rapid camshaft wear was a persistent problem with production-racing Bonnies), but to increase valve overlap with the relatively mild cams. The latter were running in needle roller bearings instead of plain, stock bearings, an old racer’s trick. Special, lighter pushrods actuated rockers that were aligned with shims and spacers rather than the stock spring-and-washer arrangement. Valves were standard size — as they were in the Thruxton racers — but Haydon noted some machining work in the ports.