“My other projects sit forlornly by, while I fawn over the steel horse from Austria...” er...

This project is a blend of the Yamaha YPVS motor with the KTM EXC Enduro bike, all dressed up in supermoto form. And Yes, you’re not reading that wrong, and some have questioned what I am thinking here... so, I’ve found that newcomers to this one probably need a little background...

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As if to confirm that heavy crash the alloy rear subframe is a bit bent, but with my changes it will need to be ‘adjusted’ anyway. With the bike came almost 2 full sets of body work and for ‘a pretty road bike’ it is mostly scrap, but will do for testing fitting before buying a full new set of panels. What’s nice about working with MX bikes is that bodywork isn’t huge money and comes coloured so doesn’t need painting.

I did pick up a straight subframe, but as I plan to use the later bodywork (see below) then I probably need to alter it anyway as the fit changed over the years.

The Engine... well, this horrible looking mess will hopefully become its engine... we'll see... It was bought by the previous owner of my RZ250 as he needed a crank and this one was deemed ok. It was flooded in a huge storm and its rusty as hell outside but inside the clutch side its been fine, so I’m hopeful it will be ok, although it will need quite a bit of work...

The wheels I bought are a set of OEM KTM SM wheels. They are very little used and came with a shortie mudguard as well... I may sell the off road wheels as this bike wont go off road once its been converted.

This engine has sat for a long time, its flywheel was very very rusty and no way would it come loose. Even slots cut in the rotor and a three legged puller did nothing so in the end I had to cut off the outer part of the flywheel in the hope I can eventually work down to the crank carefully. Obviously the flywheel and stator is now junk... shame as flywheels are getting hard to find.

Under the flywheel there was also some case damage that needs to be fixed up, more work!

The engine will also need a replacement flywheel and stator which would be interesting when it comes to sorting out the electrics as there are a few different combinations of stator/flywheel/loom to be spliced if they don’t all match up right away... To solve that I decided to run a Zeeltronic PCDI-10V system which will save that headache.

At least with a set of proper charging coils in the stator and more wires in the RZ loom the KTM will finally get useful lighting system and a battery that charges properly, although it will be much bigger for this application of course.

I’ve also been looking at how the RZ motor fits in my frame. The big problem being around the rear engine mount as I wanted to retain as much KTM as possible and the KTM uses a ‘thru engine’ swing arm bolt and the RZ doesn’t. I will need to spec up a lump of alloy or steel to fit in the gap of the swingarm and then I may tie that in with the new rear engine mounts which will need to be welded to the frame.

Whilst the photo above is slightly deceptive as it looks like great progress, the front axle is actually just a mock up. The ’99 EXC in 250 form uses the early RWU forks that use a 17mm axle, but my front wheel is slightly later from a USD fork model and uses a 20mm axle at the bearings. Sadly I can’t fix that with new bearings with a smaller ID as they’re not available and my options on reducing spacers for the axle would be 1.5mm thick and no one wanted to make me those when I drew them up, or to use a 20mm axle (I bought one to try) and then get it cut down to the sizes of the 17mm axle where it runs thru the forks, which is 21mm down from 26mm... but the 20mm axle is shorter (it’s designed for USD forks who’s legs sit inboard of the RWU units, and would need to be lengthened a little (whilst not desirable, that would be ok as it’s inside the fork leg at that point so strength isn’t so much of an issue) and then drilled to accept the capping bolt.... or to have a whole new axle made, but sadly that might blow the meagre budget. So for now I have decided to sleeve the whole axle where it sits between the fork legs. This is the strongest, cheapest and simplest of the ways forward that I found.

The joy of a Supermoto bike for me is usable power for nipping thru the traffic into and round the city. It is best with an engine that wont complain or fluff, not have too much noise but still enough to keep the car drivers aware, good brakes and good handling... this project should tick all those boxes... we'll see I guess...

Front forks are huge, solid WP 50mm units. Amusingly they look bent in the photo but they are fine actually. WP RWU forks were fitted for the last year in 1999, after that they went USD, and the axle size went to 20mm... that would bite me later...

Whilst later KTM swingarms fit this bike will have the standard ’99 unit, and will reuse the standard WP rear shock and its Brembo brake. The ’99 shock as delivered had a broken adjuster ring... how on earth do you do that to a bike! eeek! must have been a big smash, probably a big loop off of a jump...

The next stage was to test the fit of the rads and bodywork, and of course they need work...

The rads will need to sit slightly forward at the lower mounts as the frame needs re-work at that point as the YPVS engine is a twin and needs to have the exhausts pass out through wider frame rails, plus the head has a thermostat take off in this area, although that could be removed and welded up and a remote thermostat fitted.

I then set about cutting the frame. I took off the sections that run down to the footpegs and have cut some RZ parts from the old RZ frame for under the engine.

As you can see, the engine is a reasonable fit in the KTM frame once the original KTM lower frame was cut off.

The engine is a little too long in the frame by about 10mm. This is due to the fact that the original KTM engine had the swingarm pivot through it, and the YPVS motor does not have that. I can already see that 5mm or more can come off the back of the Yamaha motor which will help.

At the front the original KTM single downtube needs to be mated with the RZ lower frame which has the front engine mount. This will be  tied into the upper KTM frame using parts of the old KTM frame as they have the right bends when flipped over and used upside down.

I still have to tack and test these parts but I can see that this engine fitment will actually be a little easier than I worried it might be. The chain run isn’t that far off and whilst the engine side cases will stick out a little each side you have to expect that when you put a twin in a MX frame designed for a single.

There is also a problem with the fuel tank, being from a 2 stroke bike the ’99 250EXC tank has one side much deeper with the tap at the bottom, and one side is shallow to the exhaust pipe to pass under it.

With a twin cylinder motor the right side fits fine but the left side contacts the cylinder head. I could have either cut the inner lower portion and plastic welded it but I didnt like that idea. Whilst i can do that so its almost invisible, its a safety part and I needed another idea.

After a great long weekend in the wine country I brought home what was almost a whole KTM roller. Whilst it was pretty cheap it does need a little work, as you can see in the ebay pics of it looking ‘whole’. It had been bashed about and crashed pretty heavily a few times but the main parts were all there so it was actually good value. I could have stripped it and probably made money, but I’m not a breaker...

It all started back in the late 90’s when I bought a '99 KTM 250 EXC new. It was amazing and I raced it a little and ran it on the trails most weekends... wow I loved it.

In 2001 I wanted to reduce the number of bikes I had and I traded it for a DRZ400E when they came out so I could use my main dirty bike for Rallies as well as everything else. At the time I was using a KDX250SR on Rallies back then as the KTM was only allowed into Enduros. The DRZ was a nightmare, I had to change a lot of parts to get a half decent bike out of it - exhaust, bars, light, suspension plus carb work etc. and it was still slow and gutless after the KTM but it did have an electric foot... not a good enough trade off really... Then just as i was running-in the DRZ in they changed the rules again so the OEM DRZ tyres needed changing as well (like that would have made me a winner, sigh!) and at the same time they also decided to allow my (now sold) KTM to enter the Rallies... WTF?! With my toys well and truly cascading out of my pram I sent them a rude letter with my membership card and sold my DRZ with 167miles on it and haven’t raced since. Anyway...

As you will have guessed from reading this website, I also love my RZ/RD350s and am a huge Supermoto fan... so a while back I got to thinking... why not try and combine the KTM, the RZ and the supermoto into one bike...?! ...Yeah... not normal I know!

Since I had a spare engine with the RZ250 that I bought in bits, all I needed was a KTM roller... Not an easy thing to find in Australia... Most of this era of KTMs are still being sold for sensible money as they’re still a useful bike over here. When looking at used one the double edge sword is that the parts were all good quality on them, so they last longer and even broken up for parts they attract strong money.

A bit of searching and I found a '99 250EXC which had donated its engine, loom and some other bits to a buggy and the guy wanted shot of his old frame and all the other bits n bobs, and few bids later and  I had bought them... Sadly the parts were 6.5hrs (each way) from home so it called for a road trip! 

I suppose I should relay some of my reasoning behind why I think this will be a good bike when its done...

In it’s standard trim the KTM is lithe and slim. It is really quite light and made of high quality componentry, but has a peaky engine unsuited to road use as it needs rebuilding quite often. It runs only premixed fuel, is very noisy but it does put out 45-50bhp.

The RZ engine in 350 YPVS form has a wide powerband with ‘road usable’ power, it has a great twin engine note, and should run at 60bhp (standard) all day long reliably, with more if tuned.

I’ll say up front that this isn’t going to be one of those 'any any cost' builds... well it’s not planned to be one at the outset put it that way, just a sensible, clean and working project. After all I don’t really know if this is going to be a road bike, hill climb or sprint bike

Obviously to fit the RZ motor I needed to cut the lower rails off the frame and work out something to hold the YPVS motor in place, and after a trade of some beer with a mate I had an RZ frame sat in my garage ready to donate its lower cradle to the cause.

With all the work on the LC421 and the RZ350 the bills were starting to mount up and was looking at cost savings and was starting to think this bike might end up with a 250 motor with a standard crank as I have a freshly re-bored set of 250 barrels with new pistons, decent set of PVs and also a decent 250 head. With that in mind I painted those cylinders in case I wanted to use them.

It’s said that the Yamaha 250 makes 50bhp, which would be the same as a standard KTM250EXC, and would leave me scope to make changes later of course. Either way when the engine is built it will get all uprated bearings and new seals.

So far the engine has been stripped and the cylinders / head cleaned up and painted and the PVs cleaned and assembled...

In the gearbox there was some wear on one of the forks and dogs, but the consensus is that its not bad enough to panic about and that I should just run it... we’ll see...

The build is progressing slowly to be honest, i’ve been working on a lot of bikes at the same time (RZ350, RD350LC, DT200R, KTMDukeII640 and others), so I’m not very far down the line.

In fact my biggest hassle so far is chassis related and is because of a stupid wheel problem that KTM have given me due to changing suspension and axles so often in the early 2000’s. I finally have the parts I needed now and some specs so I can make the front axle fit, but its taken months of buying and trying axles and looking at parts books to see what i need to get done. I’m sure I should have just spec'd one and had it made right away instead of trying to find one to have cut down, it would have been quicker and less hassle... originally I started out looking for spacers but that idea was just never going to work due to the thickness. Talon in the UK have them but even though I’ve worked with them in the past they pushed me to their Aussie importer who didn’t even bother to reply to me, so i’ve given up on Talon, shame as they make good kit. 

I have noticed there are also issues with the brake pedal as the yamaha cases are wider and anyone trying this kind of conversion may need to modify those parts depending on the frame. Mine is very close on my frame even with the motor stepped over a bit (ie. lining up the sprocket to the chain). Most MX bikes are slim and so the controls are quite inboard compared to a road bike to keep the from being ripped off by off road things, so this is always going to a tight squeeze.

Located in the same area is the airbox which still needs to be fitted along with the KTM side panels. The airbox is plenty big enough for the YPVS engine which is cool.

At the front of the frame I will use a cut down RZ frame and weld it like the original KTM runners, this should be strong and simpler than some other builds i’ve seen. I need to keep i mind the rads and the other bits as the engine is taller and sits more forward than the original of course. There is a lot to think about when doing this and its easy to snooker yourself with this.

As KTM generally makes small changes each year, many of the more modern KTM parts can be retro fitted to the older models with only small changes or whole assemblies being swapped out.

Whilst the project is in reality ‘on hold’, some parts have been bought when they came available

This included a big front Brembo caliper from an Aprilia Mille R that had only driven 30km. Due to the bikes’ light weight, only one of these beautiful units will be used to grip a 320mm disk on the front wheel.

I checked the models KTM did and realised that for a few years after the model I have, the frame and bodywork is much the same on the 2 and 4 stroke models, so their tank would fit the frame. I bought one with rad guards and seat as both those other parts are different on the 4 stoke bikes. Of course, I may yet need to adjust the (or get another) rear subframe to ensure it all fits correctly.

Im not sure ‘how much tank’ I will be able to put on a bike with a twin parallel engine to be honest, remember the cyls are quite wide and tall. Perhaps this will have something like half the capacity of the original RZ... should give me 50KMs range... not really enough, and I may have to put a supplemental tank in the tail...


OFFICIAL NOTICE: I have bittersweet news... The KTMaha project is dead!

Yeah I know a bunch of guys were really keen for me to build this, myself included, but I’ve learnt a few things the past few years and one of them was when helping out a not-so-local guy (Justin, who I randomly bumped into in city the night before I wrote this notice... anyway I digress) who was building a DT350. What he discovered was that registering bikes in NSW with frame modifications is a huge chore and most engineers will just not even talk to you, let alone sign paperwork to approve it, and even if they do they will want high hundreds of dollars to do it.

So, with no real prospect of getting this machine road registered anytime soon, and the fact it would still need a serious cash investment, I pulled the plug. Sorry for those who wanted this to happen.

But, all is not lost... the parts already have new homes... The wheels and front end will all be recycled into another project I have always wanted to do, an XT500 Supermoto. The engine which is case-damaged will contribute spares to my 83 build and a bunch of other various parts will be spread over my current and future projects.

So as you can see, the KTMaha is dead... but, long live the XT500SM perhaps?

Early photo below, but you get the idea... (need to be) shortened WP extreme 50mm forks, 17inch KTM SM wheels, the rest delivered by 1980's Yamaha!

For those who want to know how the XT project pans out;


                                                                                            Click this link: XT500 Supermoto