As anyone who follows KTMs knows, when the new generation frame was introduced in 2007 it displayed a significant handling advance over the previous generation bikes. Along with the new design frame came the new generation motors in the form of the XC-W off road models and the XC-F/SX-F race bikes.
While KTM came out with two totally new motors to replace the old RFS package, both were mounted into the same basic frame. So, the new generation frame is used to outfit all the new full size four strokes.
With the new generation frame came a number of improvements in suspension and handling. The new frame is stiffer allowing the bike to track better during big hits, especially taming things like G-outs. The revised PDS shock system uses a different angle and is mounted closer to the center of the frame. The new shock can now get by with a lighter spring rate. Mounting the shock closer to the center of the frame also contributes to the improved manners of the bike by reducing the torsional stresses on the frame.
So things are good, right? Unfortunately there are many riders that have been less than thrilled with the new engine packages. The earliest versions had a number of teething problems, particularly in the XC-W versions. The issues with oil migration and auto decompression have been addressed, but there still remains a general sense that these motors will never live up to the incredible reputation that the old RFS motors had for reliability.
Frankly one of the other sentiments is that there was not really much gained in the new XC-W power plant. The overall weight and power output is about the same. In fact when comparing the new 450XC-W to the old short stroke 450XC motor it is a little bit down on power. So in some ways they have gone backwards in terms of having an exceptional off road race motor.
So it seems like there should be an answer to all this somewhere in the mix. Well that is exactly the spark of inspiration that got the cogs spinning in the mind of Greg Burns. You see, Greg is a mechanical engineer and the owner of Dirt Tricks, the makers of the famously indestructible Iron Man line of sprockets.
Greg’s inspiration was to see what it would take to shoe horn the RFS motor into the new chassis. Well in the space of one day’s work Greg had nearly the entire project completed.
Now those of us familiar with KTM know that they are very slow to change major aspects of the bikes. For example the same rear wheel will fit nearly all bikes from 1992 through today. As it turns out, another example is that the new generation motors mount into the frames nearly identical to the RFS motors. The swingarm pivot, the front motor mount and countershaft location are identical.
The old motor is a little taller but will wedge in pretty well. That leaves the list of modifications required to create this hybrid relatively small. For someone like Greg with a whole machine shop at his disposal, it is almost child’s play.
Now let us look at the details. The lower motor mount has to be slightly relocated. The frame has to be modified to accommodate the taller motor’s exhaust. The pipe mount near the shock needs to be relocated. Finally there is a flange required to get the carb to mate up to the new air box. Basically that is about it.
Dirt Tricks has fabricated simple solutions to each of these issues. They will sell you the parts, or you can send them your donor frame and they will do all the fabrication and welding for you.
I got to spend the day riding both Greg’s and Nate Delany’s official Dirt Tricks mounts. I have to say it was quite an experience. It was pretty cool to get to ride the torque master 525exc motor in the new frame. There were a couple of handling issues that I struggled with, mostly due to riding on someone else’s suspension and ergonomic set up. There is definitely a change in the overall weight bias of the bike and it may require some tinkering with set up to get everything right.
I think that if I would have had a little more time to dial in the settings the bikes could have really shined. I also suspect that the short stroke 450XC motor would be an excellent candidate for this transplant. The XC motor always feels nice and light anyway and I think it would be a good mate for the new frame.
So there you are, if you happen to find yourself with a good new generation frame sans motor (there are lots of them out there), this might be a great way to get the most out of it. For more information check out the Dirt Tricks website where they have the whole process laid out, it is pretty cool and amazingly simple for such a major project.