1983 KTM 504 MXC
"Best 4 Stroke of 1983--Dirt Bike Magazine"

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I should preface this with: I no longer own this motorcycle, nor did I ever do anything with it other than wash it. I bought it in early Winter, spring brought a streetbike accident and after I healed, I bought the bike I wanted in the first place: my ATK 605 DSES. I keep this here because I did a lot of research putting this together and there are vintage riders out there who race these old Rotax powered KTM's.

Back in the late 1970s and early 1980s, the motocross world desperately wanted (or at least seemed to want) a competitive, lightweight, high horsepower, four-stroke motorcycle. There were a number of frame kits made for the Yamaha TT500 engine but their cost left them unattainable for the average rider. The Honda XR500 was a good motorcycle but it was too porky and Honda still saw it as a playbike--definitely not a serious motocross mount.

The Europeans were usually the vendors of exotic hardware to fill such niche markets. Bombardier introduced the Can Am Sonic 500 in 1982. It featured the newly designed, Rotax built 500 cc four stroke single. The Rotax featured a belt driven, overhead cam design and 5 speed transmission. It was to be marketed to any and all manufacturers interested in using it and soon became the 'small block Chevrolet' of the motorcycle world. In fact, this engine is still used today in the ATK 600 series, the CCM 604 and a long line of Ron Wood built road racing and flat track bikes. A twin cam version of this engine also powers the BMW F650 Funduro. In short, it's a timeless, bullet-proof design.

In case you aren't familiar with the construction of European motocrossers, they tend to be built more like customs than production-line motorcycles. The best components such as Magura controls, Marzocchi forks, Ohlins or Fox Shocks often get used because they usually do not sell enough motorcycles to make engineering their own components worthwhile. These were components that riders of lesser machines would add if they had the money or at least would spend many a night dreaming about.

When KTM built a thumper to compete in the 'growing' 4 stroke market, they went all out. In early 1982 Dirt Bike Magazine was involved in the testing and development of the prototype machine. The new KTM 504 featured all premium components. A Brembo disc-brake equipped wheel was hung at the end of a stout Marzocchi 43 mm fork, with 300 mm (11.8") of travel. KTM's first generation 'Pro Lever' single shock suspension, complete with a Fox Twin Clicker shock, provided a matching 300 mm of travel out back. KTM specified a retuned version of the Rotax thumper for the 504. It featured 504 cc versus the 498 on the Can Am Sonic courtesy of an 81 mm stroke--1.5 mm longer than the Can Am. The engine's larger intake valves inhaled through  a K&N filtered Bing carburetor (36 mm) and exhaled through a quality SuperTrapp exhaust. Controls were first rate Magura parts and Acerbis built the plastics. It was a 'who's who' of trick parts and the retail price of $3080 reflected this (34% more than a Honda XR500).

The bottom line is that this was a serious motocross bike, albeit a four stroke one. Fast forward to November 1999...

I had just purchased my BMW R100GS and spent way too much money fixing it up. With Christmas approaching and the possibility of job layoff within 6 months, I was in no position to buy another bike. Nonetheless, one of my long time dreams was to have a really trick dual sport motorcycle. Not a 400 pound Kawasaki KLR 650 or a homogenized Honda XR650L, with it's electric starter and semi-serious chassis. I wanted it all: the engine, the suspension, the brakes--and just enough street legal stuff to keep me from getting a ticket. What's more, it had to be cheap. Of course I wanted it to happen in the future, when I had finished paying for the Beemer, but destiny does not wait.

Before finding the following ad at the Recycler web site, I knew nothing about KTMs. Back in 1983, the furthest thing from my mind was a $3000 dirt bike. Nonetheless, this ad's description was tempting:

1983 KTM 500 4 stroke enduro, lots of extras, has street plate, little lights, good cond, runs perfect, Lancaster area

DANG! It's a local bike. The price started at $1000 but started going down $100 a week. I suspected that the remote location (70 miles from the nearest Los Angeles suburb) and the cold holiday season had something to do with the lack of interest. After seeing the ad for a few weeks, I decided that looking wouldn't hurt. I called the guy and found that he was only in the area on weekends and worked in LA during the week. I had plans for the upcoming weekend but we arranged for me to ride out and see it at night.

Well, to say that the bike was rough would be an understatement. It was stored in his front yard and not ridden. The engine was covered in wet oil and sand (not just a film), it had awful leaks, a bent front wheel with a missing spoke, a bent rear wheel, a broken footpeg and thrashed plastic sidecovers. The charging system didn't work and it's no wonder--the conversion of this bike to 'street legal' was not done properly. It had a bundle of like-colored wires, gathered by zip ties and connected with cheap butt-connectors and wire-nuts. The Acerbis headlight glowed a faint orange when the bike was running. The aftermarket taillight and turn signals were intact but not working. There was no battery, horn or speedometer, mirror or anything else you would associate with a 'dual sport.' It was an equipment violation ticket waiting to happen. Nonetheless, it did have the coveted California license plate. Unfortunately, I had no money and the owner wasn't  negotiable on the price.

I decided to pass on it. For the next few weeks, it continued to be listed, then the price started to drop again. I decided to do some homework and figure out exactly what it was. A ride to KTM of Mojave netted me nothing. The teenager working the parts counter insisted that if it was a 1983, then it had to be a 495. I asked if that was the 4 stroke, and he said, "no, they didn't make a 4 stroke." I was getting nowhere.

The bikes in my magazines were all slightly different from one another. Each had a different exhaust, slightly different plastic or some other minor difference. Still more confusing, the KTM I was looking at, had parts that didn't match ANY of the magazine bikes. The exhaust on this KTM was damaged at one time and someone tried to weld it up. In the process, they destroyed the canister. To make it worse, the pipe it was attached to was also modified (in a very bad way), so the whole assembly needed replacing.

What I wanted was the same SuperTrapp exhaust I saw in most of the magazine ads. If it was not available, I would have to figure out my own solution to the exhaust problem. The dealer I had dealt with for years, also handled KTM. I called them and inquired to the availability of the tail pipe. KTM told the parts guy that they never sold a SuperTrapp pipe for this bike. I stood my ground based on three tests with color photos showing SuperTrapp exhausts but KTM insisted that it was never made. It was soon obvious that  if I bought this bike, I would have to become my own expert.

During the first week of December, the price of the KTM and my ability to 'float' my bills for a month, finally brought the KTM home. After much soul searching, I decided that while it was very thrashed, it's construction from aftermarket parts would make it repairable and maintainable. I also decided to make it a junkyard dog. A local self-serve motorcycle junkyard full of mid 80s junk Japanese bikes would supply the parts. A Honda Elite scooter electrical system would supply a small, DOT legal horn, turn signal switch and voltage regulator. Ron Wood Racing Products would be a source for any Rotax engine parts I would need. The Fox Twin Clicker shock could always be serviced (if it ever needed it) and the Marzocchi forks were in good enough shape that they would likely never need anything but seals and oil. Aftermarket Brembo disc brake pads had to be available and I could get the rear shoes relined if necessary. The last item was the bent rims. I decided that I could get  junkyard wheels for $40 or so and debuild them for cheap replacements.
 Identifying The KTM

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