Ask any biker what things they fear most when they’re out on two-wheels, and one of the replies you’ll usually get is diesel. So what if you carried three gallons of the stuff around in your bike’s tank when you went off for a ride? Wouldn’t it be like carrying the Grim Reaper as pillion? Apparently not, if you have a military mind.

Let me explain.
When a modern country’s armed forces mobilises for action, one of the biggest problems that the planners face is logistics. In ordinary language this means getting all the supplies, equipment, fuel, munitions, etc, to the right place at the right time to support the troops and their vehicles wherever they get sent. In the old days this meant food for the horses and the troops, and what couldn’t be carried in backpacks or in a train of wagons, was foraged from the countryside. But as armies became more mechanised the range of supplies that they needed increased, and when the internal combustion engine came on the scene, fuel and engine lubricants became essential for progress. This meant that you either had to cart it along with you, arrange for stocks to be strategically placed along your line of advance, or have very good delivery system set up. Let’s face it, you couldn’t expect to drive your regiment or battalion onto the local petrol station forecourt, flash the plastic, and fill the tanks up! And if that wasn’t enough, you needed diesel, petrol and aviation fuel to keep the whole thing going. It was a logistical nightmare.

And it still is. But the only vehicles that still need petrol are the military’s fleet of motorcycles, so small but essential stocks of this fuel still have to moved around in order to keep the whole military machine purring along. Now just suppose they had a bike that could run on diesel or aviation kerosene . . . . ?

Ah, now I begin to understand.
Enter stage left the Royal Military College of Science (RMCS) in the UK and Hayes Diversified Technologies (HDT) in the US, who between them were tasked to develop a bike that would run on either of the two fuels that make up 99%+ of military fuel supplies. If this could be done without reducing the bike’s performance, then they would have a logistical winner. And if they could improve some aspects of the bike’s performance, then it would be a win-win.

Back in 1993, the first steps were taken by RMCS to produce a “feasibility demonstrator” based upon then current diesel engine technology, to find out whether this could be used as a low-risk development starting point. This demonstrator bike used the crankcase and gearbox from an Indian Enfield to keep costs down, and a rolling chassis specially made by Eric Cheney. The results were encouraging, and from this Dr. Stuart McGuigan and John Crocker of RMCS went on to design a new engine, with development and production being undertaken by Fred Hayes of HDT in the USA. This machine used running gear from the Kawasaki KLR650, a military variant of which was already in use by the US Marines. The objective was to produce a high-torque, high-revving normally aspirated unit so as to get the most power from the size of engine, and the current version delivers around 24bhp and 33ft lbs of torque from a 584cc single cylinder unit that uses double overhead cams, four valves and indirect injection. In the modified KLR650 frame, this gives a vehicle top speed of over 80mph and a dry vehicle weight of 167kgs.

Anyway, enough of the numbers and the technology – what’s it actually like to ride! I went over to the RMCS at the invitation of Dr. Stuart McGuigan to check out the bike and to see what it’s like to go into battle on two-wheels. At first glance it looks like any other big single traillie, but without the vivid colour schemes and stickers that we’ve become used to. In fact, in it’s olive-grey drab paint its almost as though it’s still in primer and they’ve forgotten to paint it. But in a battlefield situation, you don’t really want to go out of the way to attract too much attention do you? I presume that the paint doesn’t absorb radar pulses as well – but you never know! The next thing you notice is the size of the tank, which extends down both sides, almost covering the engine and making the bike look like a Paris-Dakar refugee. As it holds three gallons and the bike does 140mpg at 55mph, its 400-mile tank range means that crossing small desserts between fill-ups is a distinct possibility! And as it’s translucent, you don’t need a fuel gauge or a warning light to tell you if you’re running low.

Getting onto the bike is the usual traillie clamber, but once you’re there, the long-travel suspension compresses and the average rider will have no problem getting both feet on the ground, The saddle is narrow and fairly firm, but is not the razor-blade affair that is often found on modern commercial off-road machinery. After all, this is a bike that will be ridden for some distances on tarmac surfaces, as well as on more rugged terrain, so you wouldn’t want to have to stand on the pegs all the time. In fact the riding position is quite comfortable, helped by the narrow rear of the fuel tank, which allows you to get a good grip on the bike with your knees. Ahead of you, you’ve got the usual cockpit instruments and lights that you’d find on any Japanese motorbike – after all, the running gear is almost straight Kawasaki, and as this bike has to go on the roads as well, there’s the usual complement of switches for indicators, lights, horn, etc, in all the expected places. But it looks a little bit more ruggedised than we’re used to seeing, and you get the feeling straightaway that this a bike that can take some harsh treatment, something that’s reinforced by the substantial hand guards.

Being diesel-powered, the starting procedure is a little bit different from normal, but thankfully you don’t have to kick it into life, as it’s electric start. You simply switch on the ignition, press the big red heater plug switch for a couple of seconds, crack open the throttle slightly and press the starter button on the right hand bar. The single turns a couple of times before firing up, and then settles into slow and steady thumping idle

From now on everything’s pretty much the same as any single-cylinder traillie. The 5-speed gearbox is a standard one-down, four-up pattern, so it’s into first, let out the clutch and away we go. You immediately notice that the diesel doesn’t pick up as quickly as a petrol engine, and takes noticeably longer to get into its stride. However it pulls cleanly with no hesitation and pretty soon we’re running at a steady 70mph along the roads around Shrivenham. Dropping down through the gears to swing around the bends, there was less engine braking than I was somehow expecting from a single-cylinder diesel with its high compression ratio; it was somewhere between a four-stroke and a two-stroke petrol engine. When I mentioned this later to Dr McGuigan, he told me that this is because diesel engines are not throttled. This reduced braking meant that the engine also took longer to slow down through the gearshifts, and if you let the clutch out too quickly, the bike leapt forward quite dramatically. Anyone watching would have thought I was doing my CBT! However, it later turned out that there was a suspected problem with the governor on the bike that I was riding, which appeared to hold the throttle open. The second bike at RMCS didn’t have this engine characteristic.

The slower than usual engine pick up meant that you also had to modify your riding style slightly, opening the throttle earlier in the corner in order to get the bike to drive through smoothly. But at the same time, the torque delivery of the engine meant that it would pull cleanly at any speed irrespective of the gear that it was in. Opening the throttle to the stop while doing 20mph in fifth didn’t faze it all, and while the acceleration(?) didn’t fire you off at lightspeed towards the distant horizons, the engine didn’t bog down or get flustered at all. And for a single-cylinder diesel, the vibration wasn’t too bad at all. OK, it was obviously a single, and you could certainly feel it through the bars, but it never really intruded and I certainly felt that riding this bike for hours on end wouldn’t cause any problems.

With a dry weight of 167kgs and the single front and rear disc setup of the standard KLR650, braking performance is perfectly adequate for the bike. Bear in mind that this bike will be operating both on and off road, so feel and progression is far more important than the initial bite of a road bike setup.
The KLR650 is a well-mannered bike in its standard form, and the fitting of the slightly heavier diesel engine has not altered this. The bike remains sure-footed at all times and you get plenty of feel from the dual-purpose MT21s. It’s a very easy bike to ride, which is no bad thing given the environment that it will be operating in, and the variety of riders who’ll be using it. In fact, once you get used to the engine characteristics you can have a lot of fun. I would have loved to have had the chance to take it off-road, but there wasn’t the time or the facilities available to do this, and my off-road skills are virtually zero. But I wouldn’t have minded getting them sorted on this bike!

So how does it fare overall? Well, the first thing you have remember is that this a machine constructed for a very specific role and against a set of criteria that wouldn’t apply to a normal bike manufacturer. So while this is a bike that won’t set the world on fire (hopefully it won’t have to be used to stop it going up in flames!), it does work extremely well in the environment it was designed for. The engine feels like it will go on forever, the frame and cycle parts look as though they could easily survive a parachute drop, and the whole package inspires a feeling of confidence. Pre-production models are currently on trial with the US Marine Corps and a number of other NATO countries, and the initial feedback is very good, and hopefully it won’t be too long before this machine goes into full production.

But that’s not the end of it.
There’s considerable potential for this engine, or a smaller variant of about 400cc, in bikes for third world countries. It could also power all-terrain-vehicles (ATVs) or pumps and generators in stationary applications, where its ability to use “pink” diesel would make good economics. So, the mixture of diesel and bikes isn’t quite so bad as you first thought – just so long as the fuel tank doesn’t leak!
And finally, if you’re thinking that you might like to get your hands on one of these bikes, there is a possibility that a civilian version could go into commercial production sometime in the future. This is totally dependent upon the military bike going into service, and then HDT will be fully committed to supplying the military initially, so there’d be no commercial sales for at least another two years after that. So you can keep your cheque books closed for the time being, and then get into the queue behind me!

My thanks to Dr Stuart McGuigan and John Crocker of RMCS for their time, and for giving me the opportunity to ride an extremely interesting machine.

DH