Triumph 1925 Model SD 550 cc 1 cyl sv

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Triumph 1925 SD  550 cc side valve frame # 342239 engine # 103811

 

The SD (Spring Drive)  was in fact a somewhat modernised version of the famous model H, which had grown out of the “Trusty” veteran Triumph. By the mid-twenties belt drive was losing its appeal to many motorcyclists, so Triumph designed a model with chain secondary drive. 
The primary chain is protected by a well-engineered  aluminium case and runs in an oil bath to minimize maintenance of chain and clutch. The powerful 550 cc engine (bore x stroke =85×97)  has lots of torque. 
The machine is equipped with three speed  Sturmey Archer gearbox,   26×3 beaded edge tyres and  Bosch magneto. 
There is a full acetylene lighting set on board.
 
This older restoration SD is an interesting  example of a vintage British machine in the popular 500cc class. It’s a good runner.