Erzberg Hammer: KTM 890 SX-F Dirt Bike!

From JZ Handmade: 120-hp / 290-lb Duke-Powered Dirt Bike…

In 2019, we featured the KTM 1290 “Super Enduro R” of legendary Czech off-road racer Jiří Heiník — a 180-bhp off-road monster built to compete in the multi-cylinder Desert Bomber class of Austria’s infamous Erzberg Rodeo, one of the toughest, most notorious hard enduro races on the planet. Built by our friend Jan Žuži of JZ Handmade, the massive KTM — nicknamed the “Excavator” — remains one of the most popular bikes we’ve ever featured. 

Now countrymen Jiří and Jan are back with another staggering twin-cylinder Erzberg weapon, the KTM “890” SX-F you see here — essentially a KTM 250 motocrosser with the 890cc / 120-bhp parallel-twin from a Duke 890 R shoehorned in!

“Jiří wanted to build a special bike for Erzberg’s two-cylinder bike category — a bike no one had ever seen, because it didn’t even exist until now.”

As you might imagine, it took a load of custom fabrication to mate the monster engine with the motocross chassis, especially since Jan and Jiří wanted to preserve as much of the OEM look as possible. At first glance, the bike looks like any other four-stroke KTM motocrosser…until you realize the monstrous heart lurking inside the tight confines of the frame.

Starting with a brand-new 2022 250 SX-F, Jan cut apart the frame from the head tube back and used the various sections as the basis to weld up a frame that would fit the Duke engine, which also necessitated widening the swingarm. Other highlights include the aluminum fuel tank (inside the subframe!) and airbox, bespoke radiators, custom titanium exhaust with Akrapovič silencer, custom wiring loom and engine guard, and much, much more.

Jan says the bike weighs just 133 kg (293 lbs) with 1.7 gallons of fuel — nearly 140 pounds lighter than a Duke 890 R with the same 120-hp engine!

“It is gnarly and insane, but it can also ride surprisingly smooth and calm just like a regular 250f dirt bike…and I can also imagine that with a road-legal plate and supermoto wheels, it could be the bike of the millennium ????”

Below, we talk to Jan for the full details on this 120-hp motocrosser, with more great shots from Jakub Frey (@jakubfreyphotography)!

KTM 890 SX-F: Builder Interview

• What’s the make, model, and year of the donor bike?

The bike is actually based on two models: 2022 KTM SX-F 250 2022 chassis and 2019 KTM Duke 890 engine.

• Why was this bike built?

It’s a customer project and that customer is one of the Czech off-road legends, Jiří Hejník — the 67-year-old gentleman who owns a KTM Super Duke 990 supermoto and Super Duke 1290 dirt bike…and he races all of them, for example the Erzberg Rodeo or Pikes Peak Hill Climb.

• What was the design concept and what influenced the build?

Jiří wanted to build a special bike for Erzberg’s two-cylinder bike category — a bike no one had ever seen, because it didn’t even exist until now.

• What custom work was done to the bike?

For the chassis geometry, we copied the KTM SX-F 250 (2022). And from there, almost every main component of the bike is completely custom and bespoke.

 

For example, we used the SX-F 250 OEM steering tube, but I completely built up the rest of frame using cut sections of the OEM 250 frame.

The swingarm had to be widened because of the bigger engine, and the radiators are bespoke. 

The aluminum fuel tank is actually hidden inside the OEM subframe.

The airbox is made from aluminium, the wiring is bespoke, and the bike has a bespoke titanium exhaust system — we used an Akrapovic Ti Evolution muffler, but the rest of pipes is completely my work. Bespoke engine guard, shifter lever, and so on.

Finally I have to mention that apart from the Duke 890 engine, we used only brand new parts for this project, so we cut up a brand-new SX-F 250! ????????

New wheels, triple clamps, just everything is new and fresh ????

• Does the bike have a nickname?

This one not yet, but the previous 1290 dirt bike is usually called “Excavator” ???????? and Jiří still owns it…

• Any idea of horsepower, weight, and/or performance numbers?

We know now after some testing the wet weight with 6.4 liters of fuel is 133kg — and also we know that the KTM Duke 890 has about 120hp, so we can diplomatically say 120hp and 130kg.

• Can you tell us what it’s like to ride this bike?

It is gnarly and insane, but it can also ride surprisingly smooth and calm just like a regular 250f dirt bike…and I can also imagine that with a road-legal plate and supermoto wheels, it could be the bike of the millennium ????

• Was there anything done during this build that you are particularly proud of?

In the case of the fuel tank and exhaust, the main challenge was space…because from the very beginning, we wanted to preserve the original KTM look, to use OEM plastic, designs, and so on…

• Is there anyone you’d like to thank?

Of course, Jiří first for this fuckin’ crazy idea and also for funding this big project. And also to my girlfriend and of course to my mate Jakub Frey (@jakubfreyphotography), who did all of the photography.

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Photos: Jakub Frey (@jakubfreyphotography)