Austin Seven Powered Motorcycles an Overview by Titch Allen
Source - The Association Magazine 1998B
Titch Allen will be known to readers, not only as a contributor to this magazine, but as founder of the Vintage Motor Cycle Club. Titch has been known to compare the roughness and noise of the Austin Seven engine unfavourably with the smoothness and silence of a vintage motorcycle engine (yes, really!), so I felt bound to send him a copy of the preceding article, drawing attention to the bit about the vibrationless power unit and the minimal engine noise. Well, I had to laugh too, but it's all relative. Titch, bless him, responded with the following notes. Ed. (The Association Magazine 1998)
Quite a few Austin Seven engines were fitted to motorcycles by engineer enthusiasts, particularly in the later thirties and during the war, but only one manufacturer, George Brough, went into production with one (if you can regard an output of nine as production). He used the complete two bearing engine plus clutch and three speed gearbox and, as is well known, ran the prop shaft between twin rear wheels either side of the crown wheel and pinion. It was intended for sidecar work only though it could be ridden solo with knack and soft rear tyres.
George's own prototype had a warmed up engine, 60 thou bore, high compression alloy head and twin carbs, and was capable of 65 mph with sidecar. Production models seem to have had standard engines and a maximum not much over 50. Legend (probably put about by George) has it that Sir Herbert had agreed to sell him engines, but it seems more likely that he bought second hand engines and rebuilt them. Certainly his own hot job started that way.
As a sidecar outfit the Austin Broughs fell between two stools registration-wise. The MoT's Construction and Use Regulations regarded the twin rear wheels as one because they were less than twelve inches apart, but local taxation offices insisted the outfits were four wheelers and had to pay car tax. Well, they would, wouldn't they, on the basis of if in doubt, charge the higher rate. Not that a man who could afford a Brough would have been that worried, but he would have been worried about the lack of performance compared with a bike engine of that capacity. The tax snag made a good excuse for George to drop the model after he had wrung a lot of publicity from it.
I rode a couple of them briefly and they were very disappointing; a decent Chummy was a lot more fun. But an Austin Brough sidecar outfit was the last machine George rode - at a parade at Mallory Park - before he died a few months later. I know - I was riding shotgun on the back!
Most DIY constructors of Seven-engined bikes ended up disappointed with the performance and many had boiling problems because the front wheel and mudguard blanked off a lot of a front radiator. Jackson, I see, placed his radiator under the scat; it must have been nice for him in the winter!
The only Seven engined bike that impressed me was built by an old workmate, Bob Collier, an ace at special building. He built the engine into a simple light frame for sidecar trials and achieved a good power/weight ratio. With low gearing it could fly through mud, but the trouble was, this soon blocked the radiator, which boiled dry. Not to be beaten, he hacked off the water jacket, welded fins to the bare cylinders, and went air cooled. O.K. for a while until the oil burned on the cylinder wall next to the valve chest area where he couldn't weld fins. This was scraped off in flakes of carbon by the piston rings and bridged the plug points. After that, he went back to bike engines.