Gunbus: Big is the New Black

Written by  Story by Buck Manning and photo courtesy of Daniel Predoi Friday, 15 December 2017 00:00
Published in Ultra Customs
If there was any motorcycle ever built that should have its own theme song preceding it to a destination, this is it. Think the opening song from the movie Rocky or maybe even the late Isaac Hayes cooling his way through the theme from Shaft. Speaking of movies, I can only imagine that Gunbus 410 rolling into town would initially cause the same look of terror to come over the faces of onlookers as when Godzilla rolls into town. The sound of all 410 cubic-inches of combustion bellowing out from just two cylinders, even at idle, would do that.


Now imagine a pack of these riding into town. Gunbus is not a one-off custom if builder Clemens Leonhardt, owner of Leonhardt Manufacturing in Eppingen, Germany, has any say. It’s intended to be a production bike for those fortunate enough to not only have the inclination to have the biggest bike in any town, but can afford its price of entry. That’d be a princely sum of 235,000 euros or $302,640.05 at current exchange rates, a busload of money no matter what currency it’s in. You could buy a new 2009 Ferrari 599 GTB Fiorano for about the same dough, but if you’re craving attention, the Gunbus wins hands down.

So what do you get for your Gunbus money besides all the attention and never-ending questions you could ever ask for? Well there’s a handmade huge backbone, twin-downtube chromoly frame featuring a beefy aluminum swingarm whose dual shocks have their work cut out controlling this monster. Up front, Clemens can’t give a call to Mean Street for his front end, so he’s built what he calls a trapezoidal fork tempered by a single shock working off linkage. Clemens whipped up an aluminum gas tank that makes a Boss Hoss’ look like a peanut tank and aluminum fenders to match.

Making a very big bike even bigger-looking is rolling stock inspired by rubber from something with Boeing written on its side. One look at those Macy’s Parade balloons tells you that a German company called RIGDON supplied the 38” tall front and a 42” rear tires. All of a sudden, the formerly wide 360mm tire on the back of your bike looks tiny in comparison. The 15”–wide rear wheel is a mag-style to handle the torque while up front Clemens machined a hub for the spoked wheel that dwarfs the 310mm disc and ends up roughly the size of a dresser wheel. From there, the spokes are laced to an 11” wide rim. The vented and drilled, wavy-style triple discs in conjunction with eight-piston calipers do their best to bring this machine to rest. Hopefully on level ground as even with a reasonable 31.5” seat height, you’re still going to be holding up over 1400 pounds.

The heart of this baby is the Leonhardt Manufacturing 410” V-twin engine fabricated with a custom cast crank and cases mated to a pair of cylinders from a nine-cylinder radial engine. This article could also be technically the first time Barnett’s Magazine has featured a BMW as these 6.14” bore and 6.93” stroke jugs are off a Junkers Ju 52 that had an engine built by BMW under license from Pratt & Whitney starting back in the ‘30s. The two-valve pushrod engines powered tri-motor transport planes we’ve all seen in WWII movies. The finning and castings are simply gorgeous. Clemens sorted them with his own twin 70mm throttle bodies with forward-facing velocity stacks and an elaborate engine management system with closed-loop lambda control for the EFI and even includes a catalytic converter as part of his 2-into-1 exhaust. Gunbus an emissions friendly beast?  Who’d a thunk? Twin sprockets and a duplex roller chain pass the 350hp and 524ft-lbs of torque to the three-speed with reverse (you betcha you’ll need it) tranny.

Just in case you feel a standard Gunbus doesn’t command enough attention, Clemens has future plans for making a sidecar available for an even more imposing ground-covering presence. Price not available at press time, but if you can afford the bike, you probably don’t care. 

Builder: Clemens Leonhardt of Leonhard Manufacturing

Taking a road trip through the hilly area of southwestern Germany, you could end up in the pretty little town of Eppingen and have no idea that like in an old black and white horror movie, there might be the monster of all monsters lurking around a corner. Eppingen is famous for its beautiful timbered houses and a known history going way back to 985, but all of that just might be history if a local guy named Clemens Leonhardt has his way. As the owner and talented head guru of Leonhardt Manufacturing, Clemens has the knowledge and skills to delve into just about anything his unbridled imagination leads him to.

Whether it’s classic cars, motorcycles, airplanes, or all-out Porsche sports racers, Clemens Leonhardt and Leonhardt Manufacturing are ready and willing to do whatever is necessary regardless of how tough the challenge might be. Compared to some of his past ultra-high tech projects, producing Gunbus could almost be considered one of his easier projects. From the other projects that he’s done involving manufacturing his own cranks, rods, and cases, adapting radial aircraft cylinders was right up his alley, although on a much larger scale than normal for a motorcycle This is a lot more than just making a bigger scale custom motorcycle, though. Where he’s taken this to a new level is making it street legal in European countries with almost impossible regulations that must be met. Instead of just sticking some carbs on this, he’s developed his own emissions sensitive fuel injection and incorporated a catalyst to meet emissions regulations. Take a close look at the photos and you’ll see that this bike is sporting a license plate. That couldn’t have been easy to earn that from the uber-tough German TUV standards for road machines. More info and pics at


Owner: Clemens Leonhardt
Year/Make: 2008 Gunbus
Fabrication/Assembly: Leonhardt Manufacturing
Engine: 410" 45-degrees V-twin
Cases: Clements Leonhardt
Rods: Clements Leonhardt
Pistons: BMW 132 radial
Cylinders: BMW 132 radial
Heads: BMW 132
Cam: BMW 132
Ignition: Dual ignition
Carb: Dual 70mm throttle bodies
Air Cleaner: Velocity stacks
Transmission: 3-speed w/reverse
Primary: Clemens Leonhardt/Duples roller chain
Clutch: 3-disc dry clutch
Frame: Clemens Leonhardt
Rear Suspension Clemens Leonhardt
Forks: Clemens Leonhardt
Front Wheel: Giant 80-spoker
Rear Wheel: Biggest mag ever
Front Tire: 38"diameter RIGDON
Rear Tire: Even bigger 42" RIGDON
Front Brake: Dual 310mm disc w/ 8-caliper pistons
Rear Brakes: 310mm disc w/8-caliper piston
Fuel Tank: Clemens Leonhardt
Oil Tank: Clemens Leonhardt
Fenders: Clemens Leonhardt/Aluminum
Handlebars: Clemens Leonhardt
Headlight: Giant Tri-light
Taillight: Clemens Leonhardt
Hand Controls: Clemens Leonhardt
Foot Controls: Clemens Leonhardt
Seat: Clemens Leonhardt

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