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
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.
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
HESPERIA CA 92345
Telephone: 760 947 3140
FAX: 760 947 3142
Dr STUART McGUIGAN
Director of Engineering Design
Royal Military College of Science
SWINDON SN6 8LA
Telephone: +44 (0)1793 785348
FAX: +44 (0)1793 783192
1. See web site: www.royalenfield.com
2. Design and Construction of a Diesel Powered ‘Technology
Motorcycle, S J McGuigan, J M Crocker and A C Arnott,
SAE Paper No 982051, presented at International Off-Highway and
Conference, Milwaukee, Sept 14-16 1998.