Vintage Thing No.17 - Dirt-track Douglas

Of all the motorcycles at Wiscombe last weekend this was the one that I liked the most. And there were a lot that I liked very much. It's a much modified dirt track Douglas and it's one of those bikes that the more you look at it, the more you notice interesting details about it. I also had the chance to talk to Malcolm Herwin who was campaigning it.

Malcolm (wasn't he Ogri's mate?) only recently put the bike together. It had been chopped around a bit for grass track racing but that has subsequently added to its specialness. Dirt track Duggies were incredibly popular from the earliest days of speedway. Their long wheelbase and low centre of gravity suited the new craze and in 1929 alone over 1200 were sold. But the JAP 500 single soon rivalled Douglas' early success and riders adopted a different style to suite the more top heavy vertical single. Douglas DT5 500s grew obsolete as the company lurched from one financial crisis to another throughout the 30s. DT5 engines were still highly regarded and Malcolm explained how they became sought after to power the DIY aircraft of the Flying Flea craze. Consequently, very few dirt track Duggies survive.

The frame on Malcolm's bike has had the two top tubes pinched together. Normally there would be a swan's neck curve down from the headstock and then they would run parallel back to the seat post. The fuel tank would then sit between these tubes.


Malcolm added little nylon wheels to the leading corners of the square engine cradle as he thought the frame might dig in on cornering. As we were discussing this we saw that these wheels were indeed well scuffed. Malcolm seemed quietly pleased. "I can REALLY ride it now," he said, " without getting pitched off."

The front wheel is off a Velocette and the rear wheel is from an Ossa. The gearbox is a Norton. and mounted over the rear cylinder and I particularly like the way the primary chain goes up to it.

As this bike's used for sprints and hillclimbs a large tank is not required. Malcolm runs the Duggie on methanol. This has a lower latent heat value so has a much softer bang although the bang is bigger. Much higher compression ratios can be run quite safely and the rearward facing pot doesn't overheat. In fact Malcolm said that after a run he could barely touch the induction pipes downstream from the carb because they were so cold. Very often they would be covered in condensation and sometimes ice.

The only downside to this miraculous fuel is the quantities one gets through. Much bigger carburettor jets are necessary. When one of my Vintage Things was running on methanol with its previous owner he said he had to get extra large jets that ensured neat methanol would run out of the exhaust if the the throttle was opened up with the engine off.


Malcolm told me that a run up the 1000 yard course at Wiscombe and a return trip back to the Paddock was using a third of a litre! I didn't like to ask him how much methanol was a litre.

He told me the small tank made it less likely that he'd run out of fuel. I quizzed him about this and he explained that small amounts of fuel in a large tank could surge so badly on the hills and corners that the motor could die.

But it's the engine that sets these Douglases apart. I really like their vintage appearance with their coarse finning, exposed valve gear and spindly pushrods. The external flywheel is a thing of beauty, too, while on the other side is a gauze covered airbox. I'm no expert but I think those are modern carbs. Original fitment would have been a pair of 15/16" AMACs. Bore and stroke is 62.25 x 85mm and there are hemispherical cylinder heads and good porting so despite the air of antiquity the spec is quite high.


There's a wonderful hand made quality about these motors and an originality in the thought processes in the minds of the men who designed and built them. Try here for more info on Douglas motorcycles.