The LC4-50, and how it happened!
Rally Raid Products Ltd evolved in 2010 after John Mitchinson & Wesley Beane designed and made the first plastic moulded EVO1 fuel tanks and fairing kits to suit their KTM 690 Enduro bikes, and has since been instrumental in expanding the business by designing, manufacturing and testing many Rally, Overland & Adventure parts to fit the popular KTM 690 Enduro.
The business originally started with the EVO1 Rally kit, which was soon adopted by KTM 690 owners, in a modified Adventure version, as the most popular auxillary tank & fairing kit produced for this mainstream large capacity dual-sport bike, used extensively by the ADV community for long-distance trips.
All of Rally-Raid Products parts are designed and manufactured in-house, in conjunction with it’s parent company, Masplas Mouldings Ltd, which is a plastic-injection moulding and precision engineering business, being established for over 25 years in the UK.
The birth of the LC4-50 idea came after competing in the Tuareg Rally 2012, which had become an annual event for both John & Wes over the last few years, when they were discussing alternatives to factory 450 rally replicas, with their inherent high costs and maintenance schedules and converted 450 enduro/MX machines, fitted with various after-market fuel tank arrangements and navigation towers and fairings.
It was very obvious that the KTM 690 Enduro bikes raced by themselves, along with the KTM 690 RR (which shared the same LC4 motor) and many other riders in these North African rallies, plus many thousands of adventure riders around the world, experienced very few mechanical problems, and the added advantage that the LC4 engine had very long service intervals meant it was the obvious choice as a basis for a privateers Dakar bike.
The only problem was the fact it was over the new FIM 450cc limit, but in a “eureka” moment they realised that by reducing the existing stroke from 80mm to 55mm, but retaining the standard bore of 102mm, it would create a new capacity of 449.6cc…….perfect.
The question was, how to do it ???
So the first thing to do was take a KTM 690 crankshaft, split it apart, then weld a steel “plug” into each crank web where the original crankpin went, and CNC machine a new crankpin hole 12.5mm nearer the centre of the crank, this gives the required reduction of 25mm in stroke that was needed.
The next step was to approach Cosworth Engineering, the world-famous race engine development company, who are only 15 miles from Rally Raid Products HQ, and convince them that our idea to take an already proven rally motor, reduce the capacity and reduce power outputs, was feasible.
As they were keen to point out, we were asking them to do the complete opposite to what most of their clients want (more cc’s and more power), but after running our proposed new motor specs through their computer model it was established that the ultra short-stroke configuration (nearly 2:1 oversquare) would give “adequate” peak power, but should produce a very flat torque curve. This would be ideal for off-road riding.
The biggest problem was to design a new piston crown that would intrude into the existing 690 cylinder head and reduce the head volume at TDC, this was needed in order to maintain the 11.8:1 compression ratio from the 690 spec into the 450 motor, something that could be difficult to achieve as we were now only forcing 450cc into the same cylinder head instead of the previous 654cc. If we kept the OEM piston design, coupled with the new smaller swept volume of 450cc, it would give us only about 8:1 compression ratio.
Cosworth came up with a new crown design that we used on the prototype motor, with the welded-up and remachined crank. Rather than have a small batch of new design pistons CNC machined, we decided to TIG weld the OEM piston crown and CNC machine the new crown form on using our own in-house CNC equipment, in order to minimise costs on the project.We were always sure our idea would result in a running motor, but would it produce useful power for us to use in a rally?
The only other part of the jigsaw was to find a con-rod 12.5mm longer than the OEM item, so that the TDC position would remain the same as the original motor, as we wanted to make a kit that could use the existing barrel and cylinder head. The actual rod used on the prototype motor came from a GM500 speedway engine, after much searching for a suitable item. Once we had the first prototype crank assembly and piston it was sent to Torque Racing, who have become partners in this exciting project, to fit the new parts into a spare KTM 690 LC4 motor we have as a spare on our rally excursions.
Martin Wittering, of Torque Racing, had the motor built and fitted into a donor KTM 690 Enduro in no time at all. The bike started first time, and sounded just like a “mini” 690, and initial road tests showed promising power, but vibration was very bad, but this was expected due to a welded-up crank that was not designed for the new short stroke.
However, enough confidence was gained to order a production crank, con rod and piston for us to compete in Tuareg Rally 2014 in Tunisia with the LC4-50, exactly 2 years after the idea was born.
After much searching for a company who could manufacture a precision billet crankshaft assembly, we were introduced to A&M EDM Ltd. based in the West Midlands. Tim Shires took on the task of designing a new crankshaft using the 690 crank as a reference but having to come up with a new design to suit the LC4-50 shorter stroke and longer con rod. Tim ran nearly 100 different simulations before arriving at the final design, to give the best balance of strength and lightness to suit the new motor.
The new crank assembly was made 20% lighter than the OEM part to help the smaller motor spin up quicker, but by careful design and choice of steel it was also made 20% stronger than the 690 version.
The first production motor was fitted into one of our own EVO2 Rally bikes the week before leaving for Tunisia, and once there we completed over 700km of testing, with no problems, apart from not being able to re-map the fuel injection before leaving the UK.This meant the bike’s fuel injection system ran very rich while on the rally, but we were confident that a session on the dyno when we returned home could improve this.
Once back, an initial day with Dave Woods Racing using their dyno and Tune ECU software gave us a massive improvement over our first settings.Dave was confident that if we returned, and tried a combination of airbox and silencer combinations, that he could get it running even better.
After the final session on the dyno the following week we ended up going back to the OEM airbox (instead of our cut-down version we used on the 690’s) and a special silencer produced for us by DEP Pipes just for the LC4-50 project.This gave the best combination of torque and power for the short-stroke LC4-50 motor and we ended up with a very impressive 49.8 hp @ 7800rpm and 35.4 ft/lb torque @ 6400 rpm, both these figures were measured at the rear wheel.
Bearing in mind, that at the initial conception stage of this project we would have been happy with an RFS-engine amount of power, around 40 hp, we have ended up with an impressive almost 50 hp, but more importantly, a very smooth torque curve, which for the “clubman” rider we were trying to target for this machine, is the essence of an easy to ride off-road bike.
After a long 2 year development, interrupted by the tragic loss of 2 of the closest colleagues and friends from our close-knit team of rally riders at Rally-Raid Products, it was a bitter-sweet moment to take the bike out on the road for its first full test run after all the dyno work transformed it from when we ran it in Tunisia.
It is a testament to all those involved in our LC4-50 project that a small group of highly-motivated, enterprising riders and engineers can produce a bike that stands alone in the choice of bikes available to prospective Dakar competitors, and is true to our original idea.
That is, to offer a bike that retains all the outstanding features of the KTM 690 LC4 motor, reliability, serviceability,ease of riding but can still compete with the current crop of 450cc rally bikes available,even with the fitment of our short-stroke customer kit but without any loss of those advantages of the KTM LC4 engine that we wanted to retain. The bike weighs in at 156kg (inc all navigation equipment, but without fuel)