For Immediate Release - Diesel Press



The programme by the Royal Military College of Science [RMCS] and Hayes Diesel Technologies [HDT] to design and develop a diesel motorcycle was undertaken to meet the requirement for all NATO armed forces to operate their entire inventory of powered equipment on either diesel fuel or aviation kerosene. This capability has major logistic advantages in obviating the need to carry other fuels to battle, and the lower flammability of these fuels compared to petrol greatly reduces fire hazards.

The design and development programme is being carried out by RMCS and HDT under contracts sponsored by the United States Marine Corps [USMC] and the UK Ministry of Defense.

Military motorcycles are used both on the battlefield, and for roadwork such as convoy escort, policing and courier duties. An "all-round" on/off-road performance capability is thus required.


Design and Development
Dr Stuart McGuigan and John Crocker of RMCS designed the diesel power unit for the bike, with development and production being spearheaded by Fred Hayes of HDT. Full collaboration between HDT and RMCS is being maintained throughout the programme.

The aim was to produce an engine having realistic power output and performance characteristics for the duties outlined above. This is achieved by utilizing state of the art high-speed automotive diesel engine technology in the design of a single cylinder engine. (Other attempts at producing diesel-powered motorcycles based on industrial diesel engines (e.g. Ref.1) have not achieved viable power output and performance).

To achieve the required performance, the objective was to produce the best possible torque without resorting to turbo charging, which is impracticable for this application at present, and the highest possible engine speed to maximize the power output. To this end, the engine uses four valves and an indirect injection combustion chamber. Indirect injection also gives lower combustion pressures – enabling a lighter engine construction, less ‘diesel knock’ and reduced particulate emissions.

The military diesel motorcycle is based on a Kawasaki KLR 650 petrol-engined trail bike, a military variant of which is already supplied by HDT for service with the USMC. The engine design is founded on a technical feasibility and ‘technology demonstrator’ programme instigated by RMCS in 1992 (Ref. 2). This programme established that state-of-the-art automotive diesel engine technology could be employed, at low technical risk, to provide a viable power output from a naturally aspirated engine unit suitable for packaging in a motorcycle. Though the current engine has been designed specifically for this application, standard Kawasaki components have been incorporated, where possible, to keep overall production cost to a minimum. A special fuel injection pump, developed by Unique Injection, enables the desired power and throttle response characteristics to be achieved. The primary drive and gearbox are Kawasaki assemblies, modified to account for the power delivery characteristics of the diesel engine. Starting is by conventional motorcycle electric starter, with the aid of a decompressor during cranking. A glow plug is provided to facilitate cold starting.

The engine is a single cylinder four stroke with a four valve cylinder head, which displaces 584 cm3, and currently produces some 18kw (24bhp). A multi-cylinder engine was rejected as unnecessary, on grounds of increased weight and because diesel engines work less efficiently in small cylinder sizes.

The bike has a top road speed of around 80 mile/hour, and general levels of performance and acceleration are comparable to a conventional 250 cm3 petrol-engined bike. However, the low speed torque of the diesel engine is outstanding. The need and desire for gear changing are thus much reduced, which aids cross-country riding over difficult terrain and also facilitates the training of military riders who are new to motorcycling. Even experienced riders use the gearbox to a much lesser extent than with petrol-engined bikes. When the diesel bike and a more powerful petrol engined machine are ridden cross-country at speed by the most competent riders, the petrol machine struggles to maintain the pace of the diesel. In the most arduous conditions, the torque characteristics of the diesel engine enable speed to be maintained where the petrol engine machine is slowed considerably.

Another important benefit of the diesel bike is improved fuel consumption. The extent of the advantage, compared to a petrol bike, depends greatly on conditions. However, typical overall consumption will be some 50% superior to a typical petrol-engined machine. This enables a reduced fuel tank capacity for a given range, so that although the dry weight of the bike is a little greater than a petrol-engined equivalent, the all-up weight, including fuel, will be similar.

Pre-production motorcycles are now under test by the USMC and have been very favorably received. Reliability to date has been excellent. Further testing will take place as the specification is refined to full production standard. Delivery of production machines to the USMC for service, and conversion of current in-service petrol bikes, will commence following full user evaluation trials. The UK Ministry of Defense and the defense procurement authorities of several other NATO countries have also expressed interest.

Commercial Potential
HDT and RMCS also see great potential for similar diesel engines beyond the military motorcycle application. Possible commercial development and marketing opportunities include:

Motorcycles for the Third World
In countries where motorcycles are still widely used for every-day transport, the improved fuel economy of a diesel bike, perhaps of somewhat lower performance than the military unit, would bring major economic advantages and conserve scarce fuel resources.

Lightweight All-Terrain Vehicles [ATVs]
The use of light four-wheeled ATVs (‘quad bikes’) in agriculture, horticulture and forestry is expanding rapidly in many countries. The motorcycle engine would be ideally suited to ATV applications and enable users to employ a common fuel with tractors and other implements, achieve much improved fuel economy and take advantage of tax-free agri-diesel fuel.

Lightweight, High Output Industrial Engines.
The motorcycle power unit would form an ideal basis for a light industrial diesel engine for powering pumps, generators and similar portable industrial equipment. It would offer a power-to-weight ratio around twice as good as current small industrial diesels. Development of the engine for this type of application is already under active consideration.

Hayes Diesel Technologies
10844 ‘E’ Ave, Suite A1
Telephone: 760 947 3140
FAX: 760 947 3142

Director of Engineering Design
Cranfield University
Royal Military College of Science
Telephone: +44 (0)1793 785348
FAX: +44 (0)1793 783192

1. See web site:
2. Design and Construction of a Diesel Powered ‘Technology Demonstrator’
Motorcycle, S J McGuigan, J M Crocker and A C Arnott,
SAE Paper No 982051, presented at International Off-Highway and Powerplant
Conference, Milwaukee, Sept 14-16 1998.


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