Gunbus 410 the largest drivable motorcycle in the world

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Gunbus 410 by Clemens F. Leonhardt

INTERMOT countdown part 6

Raise the curtain on the largest two-cylinder motorcycle in the world. The Gunbus 410 has a V2 with 6.7 liter displacement, weighs about 950 kilos and has XXXXL dimensions. It crowns the life’s work of its builder Clemens F. Leonhardt.

E.An eminent philosopher said there are only three infinities in the world: the infinitely small is opposed to the infinitely great. And the infinitely complex towers above everything. Welcome to the world of Clemens F. Leonhardt: "I always did what fascinated me, built what I want, not with the intention of selling it. "His Gunbus 410 is one of the many (air) vehicles of the trained motor vehicle master and aircraft builder. It crowns the “Crazy Wheels” exhibition in the much-visited Technik Museum Sinsheim. And not just because of their enormous dimensions, big as a tractor. The most powerful two-cylinder motorcycle in the world is also impressive thanks to its complexity.

Gunbus 410 by Clemens F. Leonhardt

INTERMOT countdown part 6

Cylinders come from aircraft engine

6.7 liters of displacement in the metric system are rounded up to 410 cubic inches. For comparison: our current endurance test Harley, a Heritage Classic, has a whopping 1,868 cm³, or 114 cubic inches. But in addition to the Gunbus, which is almost four times the size of its motor, the US bike looks like a children’s bike. What do both have in common? 45 degree cylinder angle. Which displacement source did the 68-year-old draw from? Well, the aircraft and vehicle manufacturer simply merged heaven and earth: The Russian radial engine named Schwezow ASch-62 fires the Antonow An-2, the most built and largest single-engine biplane on the planet. From this circular nine-cylinder, Leonhardt, as an old-school designer (“I can’t CAD design, I’m too old for that”) only operated two cylinders.

This organ removal was not a transplant, but only the nucleus of a completely separate drive. Because Clemens could only continue to use the cylinders with their heads and bumpers as long as folding rules. Everything else he built, cast and polished himself, rarely with the help of his specialist friends: four-part engine housing (milled from a 160-kilogram aluminum block), crankshaft, milled connecting rods, primary drive each with a one-inch double-duplex chain, oil pump and piston. Each of the two pistons with a fat 156 millimeters diameter weighs a full 1.8 kilograms. “It doesn’t matter, the engine turns a maximum of 2,800 revs.” Leonhardt made the crankshaft from one piece.

Engine parts for 80,000 euros

Sensational, this vertical range of manufacture. At first you are flabbergasted. The crankshaft blank made of cast steel (“Many can cast iron”), cast by a company in Pirna, weighed 50 kilograms. The finished crankshaft still weighs 43 kilos. Costs for the crankshaft and connecting rod alone: ​​36,000 euros, all parts for the entire engine amounted to around 80,000 euros. The problem: "For a long time I couldn’t find a company that could grind my crankshaft. The Maus company from Cologne did that first." The designer learned something new: "Today I would build the crankshaft from individual parts, with the shaft, crank pin and cheeks separately."

Rossen Gargolov

The cylinders and heads come from the Soviet nine-cylinder radial engine Schwezow ASch-62 for propeller aircraft like the Antonow An-2.

What other parts has the technology-loving 68-year-old bought? The Baden tinkerer had to think for a long time: “Chains, struts and brakes, tires and screws.” He designed everything else himself: frame and swing arm, (protective) sheet metal, the elaborate trapezoidal fork including handlebars (“which keeps the caster constant when braking“), Wheels, tank – all self-made. The drawing board, on which Leonhardt still planned his construction by hand, “is in my living room today”. Five years passed from the idea to the finished motorcycle. The engine is a real V2 with a crank pin and fork connecting rod. "As with Harley-Davidson, one connecting rod carries the other with it."

Next time, Clemens would build a lot lighter and more filigree. “But light is expensive.” For example, the man from North Baden would design a weaker oil pump, the current one producing a full ten instead of the necessary five bar oil pressure. “That’s why the pressure relief valve opens almost all the time.” Or would you prefer a crankshaft with roller bearings instead of slide bearings? “You just have to drip a little oil on it.” It’s a shame that we can’t listen to this rich bass, this long-throw experience (175 millimeter stroke!) Of the highest quality live here and now. But the silencer is missing, and Clemens Leonhardt would first have to do the dry sump lubrication for the oil tank. The new oil tank should be in the sidecar under the seat.

Brakes could also stop Boeing 747s

But otherwise it would be ready to drive, this over-machine. The builder is self-critical of his XXXL vehicle. “The sidecar is rather provisional, the third wheel does not yet have a brake.”It has an important function as a support: It prevents falling over, which inevitably happens with the 650-kilo solo machine when it is at a tilt angle of 15 degrees. Tried out on the crane boom. “Driving was only possible if you had a lot of courage.” The three internally ventilated disc brakes with eight-piston fixed calipers could perhaps also intercept a Boeing 747. And on the 22.5-inch rims are "wrong tires" – for a team. Clemens Leonhardt would have liked to have spokes at the back too, but they were too weak. He also milled the multi-part center star for the American truck rim himself.

MOTORRAD has three Mercedes Sprinters, around 7.5 meters long and three meters high. But nobody can pick up the Gunbus with a sidecar. The low loader for transport to INTERMOT in Cologne at the beginning of October has already been ordered. Until then (and afterwards) you can admire the fat Brummer in Sinsheim.

The builder and the technical data

The builder: Clemens F. Leonhardt is a motor vehicle master and aircraft manufacturer. At the age of 19 he won the "1000 Kilometers Hockenheim" and started working as a mechanic for the legendary designer Friedel Munch at the age of 21.

Rossen Gargolov

The builder is self-critical: "The sidecar is rather provisional, the third wheel does not yet have a brake."

Leonhardt later worked on driving tests at BMW Motorrad: “In the endurance test we drove 1,000 kilometers every day, and during the pendulum tests we often fell.” In 1972, the motorcycle fan opened an agency for BSA and Triumph, later became a pilot and drove steam locomotives.

Technical specifications: Air-cooled 45 degree V2 engine, 6690 cm³, 257 kW (350 HP) at 2,650 / min, 710 Nm at 2,200 / min, bore x stroke 156 x 175 mm, compression 8.7: 1, double ignition, two valves each Operated by cam, roller tappets, bumpers and rocker arms, dry sump lubrication, three-speed gearbox, dry clutch, tubular steel frame, trapezoidal fork, length 3.45 meters, wheelbase 2480 mm, seat height 800 mm, tank capacity 27 liters, weight with a full tank approx. 950 kg, wheels front / rear 22, 5 x 6 / 22.5 x 13 inches, price from 200,000 euros. Contact: info@leonhardt-manufacturing.de

Test drive course at INTERMOT

It doesn’t have to be one of the largest drivable special (sidecar) motorcycles in the world, smaller machines or scooters are also fun and bring a completely new feeling of mobility – especially for young people and newcomers.

Koelnmesse GmbH

From October 3rd to 7th, the big INTERMOT motorcycle fair will take place in Cologne. There will be plenty of bikes ready for test rides.

Make a cool appearance on the 50s scooter in front of the ice cream parlor or experience first experiences in terms of driving dynamics with a 125s. The advantages are obvious: easy to use, economical to use and almost unbeatable in the big city. Anyone who is up for two wheels with an engine should come to INTERMOT in October. The focus here is not only on the high-horsepower and large-displacement bikes, but also on the smaller cubic classes and scooters. And best of all: You can also try out the vehicles on the INTERMOT test drive course. So: Make sure to tick the date October 3 to 7, 2018 in the calendar!

Special exhibition "Totally crazy": On the exhibition boulevard in the corridor between exhibition halls 6 and 9 and at the MOTORRAD stand in hall 9, stand A 41.

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