On Yer Bike: Motorbikes are no longer the preserve of petrol-heads, as recent developments reveal.

With questions over their power-to-weight ratio, size and limited rpm, potential diesel engines have historically been seen as unsuitable for motorcycles. But the lure of 200 mpg-plus fuel economy continues to drive the quest for a commercially-successful diesel motorbike to go on sale.

The first diesel motorcycle built in 1904 by Jan Dopper was a fairly rudimentary affair: its two-speed BRONS-type engine producing just 2bhp at 700rpm. Further Developments led him to produce a three-wheeler in 1910 before war intervened. During both World Wars and in the intervening period, various prototype diesel motorbikes were developed primarily for military purposes but it wasn’t until the 1950s that manufacturers started to seriously experiment with machines with civilian potential. In the early 1950s, BSA built a number of motorcycles with Daimler-produced engines, whilst Arthur Sidney developed a successful 500cc diesel Norton motorcycle. Power from the aluminium-blocked engine was around 10 to 14bhp, with top speed around 55mph.

Military demand continued to drive development though, with many governments wishing to use diesel for all their military machinery. In many cases diesel engines were simply transplanted into petrol motorbikes, rather than designing a completely new diesel motorcycle from scratch. By the 1980s, many NATO forces in Europe had re-fitted their bikes with diesel engines. Air-cooled single-cylinder engines built by Lombardini were popular, with some achieving similar sub-70mph performance to petrol motorbikes and fuel economy of more than 100 miles per gallon. In 2005, the United States Marine Corps modified the M1030M1 an off-road motorcycle based on the Kawasaki KLR650 with an engine that could run on diesel or jet fuel. Further development at Cranfield University and California-based Hayes Diversified Technologies led to the production of the Kawasaki KLR650 diesel motorbike. A liquid-cooled single-cylinder 584cc four-stroke, it produced 28bhp and boasted a top speed of 85mph. There was talk of producing a civilian bike in parallel too, but that has so far not come to fruition. Perhaps due to a perceived lack of demand for a diesel bike in the Western World?


In India, however, there were no such reservations, especially as the price of diesel was so low. Royal Enfield sold 325cc single-cylinder diesel-engined Taurus motorbikes in very large numbers from the 1990s, until recent pollution laws caused production to cease, but most of them are still in running condition. And in the last few years, with the growth in popularity of other diesel-powered vehicles, companies in India, the USA, Holland and Germany, among others, have all been seeking to mimic Royal Enfield’s commercial success in a financially and environmentally-viable way.

DIY CONVERSIONS
Bespoke diesel motorcycles where a diesel powerplant is transplanted into an existing Royal Enfield motorbike are actually more popular than you might imagine, with many enthusiasts fitting engines made by Ruggerini, Lombardini and HATZ. Specialists like Pricepart Motorcycles are happy to help, and could convert your existing Royal Enfield to diesel power from around £2,500 including VAT.

CURRENT PRODUCTION BIKES
Diesel motorbikes currently in proper production include the 11bhp Sommer Diesel 462, capable of 65mph and 95mpg, and powered by a HATZ diesel motor. They are assembled by hand in small batches in Eppstein, Germany, with all of the remaining components supplied by Royal Enfield of India.

Dutch company E.V.A. Products BV started to sell their Track T-800CDI diesel motorcycle in 2009, although production has currently been halted. Priced at £15,995 in the UK, its 50bhp Mercedes 800cc engine gives the Track T-800CDI a 102mph top speed and fuel economy figures of 76mpg.

Hayes Diversified Technologies’ M1030M1 diesel Military motorcycle is currently in production for the US and other NATO armed forces including the British Army.

Based on a modified Kawasaki KLR650, top speed is 90mph and fuel consumption is rated at 96mpg. A civilian version the D650A1 Bulldog was originally intended for release in 2006, but due to increased military production demand, this is currently on hold.

French defence manufacturer HDT also makes a military diesel motorcycle the 670cc 1030M2 which can even run on jet fuel and biodiesel, whilst German company Star Twin Motors produced a 70bhp Thunder Star 1200 TDI, with a modified 1.2-litre Volkswagen Lupo diesel engine.

Elsewhere in Germany, Neander Motors have produced a twin-cylinder turbodiesel 100bhp diesel motorbike called the Neander which is capable of reaching 60mph in just 4.5 seconds and plan to produce around 60 bikes a year. And although production of the highly-successful Taurus model has now ended, Royal Enfield in India is currently developing a replacement diesel-powered bike to launch into the Indian market too.

So what does the future hold for diesel motorcycles? Small-capacity, forced-induction diesel engines are definitely the way forward, and if emissions and purchase price can be kept within sensible limits, then a contemporary commercially-viable diesel motorbike won’t be very far away. In the meantime, the technology will continue to be driven by specific military applications.