Northamptonshire based Rally Raid has taken the engine out of a KTM 690 and reduced the cc to below the FIM legal 450cc requirement for Dakar. Here we chat with the man behind the project, John Mitchinson, to find out how they did it (and it wasn’t done by sleeving)…
Where did the idea come from?
It was myself and Wesley Beane, a local friend who I’d ridden with for a long time who sadly lost his life competing with me last year on the Tuareg Rally. A year before that we were just talking about the new rules limiting Dakar bikes to 450cc, and the high cost of the factory replicas, or building an EXC based rally bike using after-market parts. Because we’d raced the 690s and we’d had a lot of them in other rallies such as Heroes Legend and the Trans-Continental, fitted with our tank and fairing kits, and they’d all to a point finished – with no reliability problems, and we already had a rally kit that fitted the 690 – we thought ‘why can’t we make the 690 into a FIM legal 450?’
KTM’s solution had been to take the 450cc motocross based engine, strengthen and modify it, and put it into the existing 690 Rally rolling chassis. I looked on that as a bit of a mechanical fudge, as to me you were losing the main plus point of the 690, which was its reliability. Myself and Wes did some calculations on the back of a fag packet and realised that with a 55mm stroke and the standard bore we’d bring the engine down to the 450cc limit. The standard bore is 104mm by 80mm to give 654cc. We calculated that with a reduction in stroke of 25mm, bringing it down to 55mm – and keeping the existing bore diameter – that the cc would come down to exactly 449.5cc.’
Why not just sleeve the engine?
If you sleeve it down it would look like a mushroom where it meets the original cylinder head, and the valves are too big so it wouldn’t work. The valves would impact on the top edge of the sleeve.
Why didn’t KTM do the same?
It was something they probably thought about, but ultimately they wanted maximum power. They’ve got the top riders and the top riders want power. At the top end an extra 2 or 3 bhp will make a difference, but they can race 800kms a day and rebuild it every night. We are coming at it from a completely different perspective. We’re not chasing maximum power. We’re not at the sharp end of Dakar. This project is all about reliable power.
What problems did you envisage with making a 450 out of the 690?
Primarily, the concern was how much power we would lose. It wasn’t a question that it wouldn’t work or not, we knew it would run. Mechanically there was no reason that it wouldn’t. The question was would it have enough gas flow at low revs, as we were running the standard 690 cylinder head and inlet tracts, designed for the original capacity. We wondered whether it would make enough power, run smoothly and be rideable or not. Also, by having an ultra over-square engine – almost 2:1 – we weren’t sure if the characteristics of that design of engine would make it too peaky to ride off-road, particularly as the focus of this bike is not some sharp-end short-course MX racer, more for someone who’s going to be riding the bike 8-10 hours a day. It’s about reliable power at the end of the day.
What does the kit include?
The kit involves manufacturing a new, redesigned crankshaft, with the shortened 55m stroke, a new connecting rod, and a new piston, with a high crown to reduce the volume of the cylinder head at the top dead centre, so that compression ratio is retained, even though there’s a reduction in swept volume.
Could you explain that?
You’ve got a cylinder – a barrel – with a piston that goes up or down inside the barrel. Whatever that cylinder is – if it’s a 50cc –then it moves 50cc of volume each time it goes up the barrel, from bottom-dead-centre (BDC) to top-dead-centre (TDC). Now let’s assume that the piston is flat-topped, which on the 690 it is, you then have the case that when the piston travels from BDC to TDC and comes up it is pushing 654cc, calculated from the 104mm bore x 80mm stroke (plus the volume of the cylinder head) into the cylinder head recess, and if that recess volume is twelve times smaller, then that’s how you get your 12:1 compression ratio. Once you know the compression ratio and you know the swept volume (654cc) you don’t need to measure the cylinder head, you can actually calculate the volume using mathematic equations.
Once I knew what the volume of the cylinder head was, I then recalculated using the shorter 55mm stroke for the 450cc motor as to what would be the new smaller volume I would need in the cylinder head. The problem of course is that you can’t adjust the cylinder head volume itself, as that’s fixed by the shape of the cylinder head design. What you have to do then is put a raised crown on the piston, as the piston effectively now only moves two-thirds of the stroked volume that it used to move, meaning that the cylinder head needs to be two-third of its original volume to retain the same compression ratio of 12:1
We did not want to have to start machining the cylinder head, so this is why we decided to add material to the top of the piston. This is called an ‘intruder’. That’s the question people ask; ‘how do you retain the compression?’ And we do it by increasing the crown of the piston. (To recap; there is less swept volume – effectively 2/3 less, therefore, in order to keep the same compression ratio the cylinder head has to be reduced in volume by an equal 2/3. This is done by increasing the crown of the piston, called an intruder).
What were the complexities?
We had to measure the valve openings. We did this by taking the rocker cover off and putting a dial gauge on the end of each valve stem, rotate the crank and every 5 degrees you take a measurement. This is to measure the profile of the lift of the valve because you’re going to have to put a pocket in the crown of the piston to prevent the valves from impacting on the newly raised piston crown. Before you do this, you need to know the lift of the valve at certain revolutions. You can obviously work out where the pockets need to be as the valves only work in one direction, but what you don’t know is how deep the pockets need to be.
To design the correct crown, you first need to know what the valve lift is at 5-degree intervals either side of TDC on the firing stroke. You have to do this because of the need to design some pockets into the piston to give clearance for the valves when opening and closing as the piston nears TDC.
If you didn’t put pockets in the crown of the piston you could, in theory, drive the valves into the crown of the piston. As a further complication, once the piston crown has been calculated to give the correct compression ratio, you have to compensate for material lost to the pockets by increasing the volume of the crown of the piston by an equal amount to that volume lost by adding the pockets.
Basically, because you’ve scooped some of the crown out to make the pockets, you have to put some back on across the rest of the crown to keep the compression up. You have to put extra metal in the middle if you like. Equally, the profile also has to be the right shape to allow the air and fuel to flow through the cylinder as well. We do all this on 3D CAD software (self-taught).
Who made the piston?
We contacted Cosworth at the initial design stage. They were very interested in the whole project. They did a gas flow analysis of the stock 690 cylinder head, and then did a simulation using the shorter stroke characteristics of the new 450 engine to give a theoretical power output. The outcome, and their concern, was that the engine at low revs may not have enough gas flow due to the cylinder head ports being designed for the much bigger 690 engine.
The ports were designed for more air and fuel. The smaller engine would have approximately thirty percent less airflow (due to reduced cc) for any given rpm. To build the first piston we TIG-welded up a standard 690 piston, then CNC machined the new crown design onto it using our own Haas 3-axis CNC milling machine. We then had to alter the standard 690 crank to give the new 55mm stroke.
And the crank?
This was done by pressing apart the standard crank, which is of a 2-stroke type design with solid con-rod and needle roller big-end bearing, something that is not normally done on these motors. If you ever did damage a big end on a 690, KTM would just sell you a new crank, not a con rod kit, as they’re not made to be split, as the design is so reliable. We then turned a steel plug to fit into the original crankpin hole in each crank web half, and welded it in place, and then re-machined a new crank pinhole 12.5mm nearer to the centre of the crank. Because if you want to reduce the stroke by 25mm, all you have to do is move it 12.5mm nearer the middle (12.5 + 12.5 = 25).
But then, because we wanted to keep the original TDC of the piston in order to make the kit simpler to fit, we had to find a con-rod 12.5mm longer than the standard connecting rod. This took some searching, but eventually, we got one from Trevor Eaden at Vega Racing, who supplied the con rod from a GM 500 speedway bike. Up until that point it’d been a fruitless search, then we find a guy in Daventry, down the road from us, with a barn full of con-rods!
Once all the machining was complete, we took the crank assembly parts to Derrick Edmondson at Edmondson Racing, Cannock, who pressed together the new crank and trued it. At that point I’ve got a welded up prototype crank, speedway con-rod and a welded up prototype piston. This was the back end of 2013. These parts were supplied to Martin Wittering of Torque Racing – long time Dakar mechanic and engine builder – who stripped a spare 690 engine and rebuilt it using the new modified crank, rod and piston. Surprisingly, it started first time! We were pleasantly surprised by the sound of the motor, it sounded more like a mini 690 than a 450, which is the best way of explaining the bike.
You can’t compare it to an EXC or a 450 Yamaha. It’s a mini 690, as it retains a lot of its characteristics.
Although the initial test run was promising, it did suffer quite badly from vibration, but this is what we expected from a welded up, non-balanced crank.
But it proved the mechanical concept, that the kit worked and that all the calculations were correct. I was perhaps only 0.3 of a cc out from our theoretical calculations when we measured the new cylinder head volume at TDC with a burette, filling the head cavity with oil through the spark plug hole.
The next step was to place an order for one production crankshaft and con-rod with A&M EDM Ltd, in the West Midlands. Our initial crankshaft design was massively improved by Tim Shires, chief designer and off-road rider at A&M, who went through nearly 100 simulations of crank design on their computer software to give us optimum strength and weight that we would need for the smaller cc motor.
It’s approximately 20% lighter than the standard 690 version. The new design of production piston was an evolution of the original design.
Once these two production parts are ready – the piston and the crank assembly – the bike was built in double-quick time by Martin at Torque Racing, and three days later it went to Tuareg Rally in Tunisia for a shakedown run.
It was a good opportunity to test it in those sandy, desert conditions. Initial results were that the bike ran very good mechanically, but did suffer from over-fuelling, which caused problems with bogging in the dunes. But we were confident that when we returned home, with some dyno work, we could eradicate that problem.
Back in the UK we took the LC4-50 to Dave Woods Racing in Aylesbury, who spent a full day re-mapping the EFI system to suit the new smaller capacity motor. The bike started with an initial run of 43bhp, but by the end of the day we were getting 48.5 bhp with a very good smooth torque curve, which was a nice by-product of the short-stroke motor.
We spent over 4 hours with the new motor being run continually up to its 8400rpm rev-limited maximum, with no ill-effects, which was very promising, as reliability was the major factor we wanted to retain from the 690 motor.
We ran the bike on the road for a couple of weeks to get a feel for the engine and then returned for another day at Dave Woods Racing to iron a couple of small dips in the power curve and so we could test a couple of different airbox configurations. By the end of the day we ended up with 49.8hp. We took a standard KTM 690 Enduro as a benchmark, and that made its claimed 59bhp, suggesting that our 49.8bhp was accurate.
Both bikes’ figures were measured at the rear wheel, using the same rear wheel in both bikes, to give an accurate comparison. Another good result was that we only lost about 10ft/lbs of torque than the standard 690, which was great news. Next stage was to pack Jenny (see break- out opposite) off on a 6,000 km test ride to Greece and back for the Hellas Rally. This involved fitting the stock wheels, tyres and indicators on to the LC4-50 rally bike, along with Giant Loop soft luggage, Martin gave it a full service, oil and filter change before she left the UK.’
John’s offering three options:
Engine Kit. The kit costs £3,800, to convert your own 690 to a 450. Anyone can effectively refresh their KTM 690 Enduro or Rally engine with this kit.
Rental Package. This offers the best of both worlds, with the bike fully prepared, with back up of the team and access to spare parts and costs £8,500 for an LC4-50.
Buy a brand new LC4-50 Rally, with Tractive suspension and navigational gear, for £18,000.
To enter the Dakar costs approximately 14,700 Euros. The LC4-50 rental package is £8,500, for a fully prepared and ready-to-go bike, with it being available as soon as you put your name down, meaning you have the bike to practice on well ahead of time, with a full refresh included prior to Dakar. Other costs include a £12,000 full assistance service team costs, which allows for a personal mechanic and driver.
Alternatively, you can do it ‘Malle Moto’, which means you go it alone, with no backup and just two trunks of kit. This is something Rally Raid is not encouraging as they’re keen to support their bikes through to finish. The total cost of entering Dakar then is around £32,500, which still isn’t cheap, but at least with an LC4-50 you have a fighting chance of finishing, rather than failing due to technical issues.
Another plus point is you convert the 450cc motor back to the full 690 spec for most of the other non-FIM rallies, such as Hellas and Tuareg, where there are no capacity limits. John concludes, ‘It’s a clubman’s bike, that’s what we’ve built this for. It’s for the guy that can only afford to do it once and wants to finish, and if you want to put your money on the best horse in the race to finish then that’s the bike. It’s not going to be first past the post, but you can be more certain of a finish. We’ve effectively taken a reliable, proven bike, and we’re actually de-tuning it. This can only add to its reliability.’
Jenny Morgan is a freelance photojournalist, travel writer, adventure rider, looking to compete in Dakar in 2015. Jenny started racing in 2008 on a Honda XR650R, entering the Tuareg Rally in Morocco. Jenny replaced the Honda with a Yamaha Ténéré 660 in 2008 and having travelled the best part of nine months on that felt that it would make a good rally bike. She fitted WP suspension and entered the Heroes Legend at the end of 2009, finishing seventh. Jenny rode the LC4-50 on a recent shake-down mission to Greece…
“I rode it out to Greece for the recent Hellas Rally, leaving on the Monday and reaching Ancona in Italy by Wednesday. The bike would cruise at 120km/h no problem on the standard airbox and standard seat. The bike is running the full Evo 2 kit, meaning three tanks, rally fairing, pretty much as you’d be racing on.
I gradually opened the bike up until I was cruising at 130-140km/h, with a maximum of 153km. At 135km/h it still feels like you’re not revving it. It feels like a big bike, like a big adventure bike. It did stutter after the second refuel, limping to the hotel, with it turning out to be a blocked fuel injector, which was a relatively easy job to fix.
When I arrived in Greece I swapped wheels and tyres, racing the bike for six days and covering approximately 2,000 kilometres. There were around 250 entrants, with approximately 120 finishing. I started off taking it easy, the terrain was mountainous and rocky with steep climbs, river crossings, technical challenges. The bike wasn’t necessarily suited to the tighter technical stuff but I was pleasantly surprised how confident the bike felt.
Over fast undulating forest tracks the bike was very relaxing to ride. On liaison sections (the stretches between the stages) the bike wasn’t a hardship to ride. I was impressed with how easy it was to manage. The nature of the bike helped conserve energy, finishing 73rd, 1st in the ladies class. I then jumped on and rode back, not even changing the oil. It had barely used any either. I certainly couldn’t have done it on a 450cc Enduro based bike. I have no reservations about using it in the Dakar. The bike gives you a fighting chance and saves you worrying that the bike will grenade, eliminating a huge stressful element.”
Triumph Fuel tank
Whilst over at the Rally Raid we had a look at their new reserve fuel tank for the Triumph Tiger 800
As well as the LC4-50, John was also keen to show us his cunning solution to extending the fuel capacity of the Triumph Tiger 800 and 800XC models. The tank is made from moulded plastic, holds eight litres of fuel and locates into the same fastenings as the pillion seat.
This means that you can interchange between the extra fuel tank and the pillion seat without any hassle. This is made possible by a CNC billet fuel adaptor plate (included in the kit) that is sandwiched between the underside of the OEM tank and the fuel pump flange, allowing fuel to flow under gravity between the two tanks.
The extra tank is connected to the fuel adaptor plate by a dry-break connector located beneath the rider’s seat, so once the fuel adaptor plate is in place (approximately 2 hours workshop time) it takes just a few minutes to switch between pillion seat and extra fuel tank. Adding eight litres to the bike’s 19-litres as standard gives a very useable 27-litres.
The fuel tank also comes fitted with an Acerbis cap and breather and has an alloy fuel tap fitted on the underside. A top rack is also fitted.