Table of contents

• Monkey 125 Four Honda Monkey with four cylinder engine
• Project start
• The first test drive
• Racing motorcycle scented toy

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18th pictures

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1/18
This little black monkey was born in an attic and feels at home on the streets.

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2/18
These two monkeys did not break out of the zoo, but live out their primal instinct in the wild.

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3/18
Pleasure for the senses: the buzzing piston drive is accompanied by a chirping, light tone from the head area and a sweet and sour smell from a shot of Castrol R40 in the gasoline mixture.

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4/18
A monkey on the grindstone: Dieter’s baby feels most comfortable on the idyllic streets in the Odenwald.

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5/18
Thought out down to the smallest detail: That “125Four”-Logo emblazoned in the tachometer.

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6/18
The result of his craft can not only be seen but also heard.

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7/18
The special monkey on two wheels goes by the name “125Four”. And who actually comes up with the idea of ​​giving a monkey a four-cylinder heart??

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8/18
Dollhouse dimension: Creator Dieter built tiny parts in his attic during his Monkey project.

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9/18
By the way, the inventor Dieter is far from finished: his next project is to plant eight cylinders on the shortened engine of a Ducati 900 SS.

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10/18
… one last look at the little black monkey and its four cylinders.

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11/18
Tinkerer Dieter Hartmann-Wirthwein, 51, and son Fabian, 21, who started his two-wheeler career at the age of four.

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12/18
The small four-cylinder hangs great on the gas and screams its pleasure out of the beetle pipe.

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13/18
This is the man: Dieter Hartmann-Wirthwein, 51 years old.

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14/18
The hand-assembled four-cylinder is hardly bigger than a handbag.

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15/18
Tiny: camshafts and valve keys in relation to a penny.

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16/18
Playmobil feeling: You sit on a toy, but you can hear and smell a racing motorcycle.

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17/18
“The Monkey is the touchstone for an even more absurd project”, explains Dieter with a grin. We are excited and throw at the end …

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18/18
This is what the result of a crazy idea looks like: a Honda Monkey with a four-cylinder engine.

motorcycles

Monkey 125 Four

Monkey 125 Four
Honda Monkey with four cylinder engine

A small amateur film on the Internet brings it to 25,000 clicks in six weeks: In southern Germany, a tinkerer has spiced up his monkey with a four-cylinder engine he made himself ?? Madness or awesome?

Rolf Henniges

09/25/2008

It came to him when he looked out the window, says Dieter Hartmann-Wirthwein. One inevitably wonders what the 51-year-old would have developed if his house weren’t on the busy main street of the small town of Rimbach. Instead of the customer parking lot of a grocery store, he might be looking at the New York skyline or the Alpine panorama.

Rimbach im Odenwald is an idyllic place on the southern German wine route with around 8,600 inhabitants. Dieter Hartmann-Wirthwein has lived here with his family for 26 years. His wife Petra drives a Moto Morini 3½, son Fabian a Yamaha R6. He himself owns a vertical shaft Ducati and a Bultaco Alpina 370 with a unique selling point: Hartmann-Wirthwein has attached a Ducati cylinder with pistons and valves to the two-stroke engine. He designed the cylinder head and camshafts himself. “When I drove up to the TuV with the thing in 1992 and wanted to register the conversion, they looked pretty stupid out of the laundry”, remembers the tinkerer. At that time, the TuV engineers were only able to measure the volume and the power: the 370 Bultaco engine is quiet and continues to produce 15 hp, except that it revs around 1000 earlier. The conversion is entered in the vehicle documents for about 100 marks, from now on Hartman-Wirthwein uses the single for trips to work. Fifteen years later, he buys a Chinese copy of the Honda Monkey.

Monkey conversion with four-cylinder engine

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Cubic capacity, cubic capacity, cubic capacity!

“Of course, the four-cylinder monkey project was a crude idea”, The trained machine designer smiles, although professionally he has to do with conveyor technology instead of engine construction. “But it should be the touchstone for an even more absurd project.” Dieter rolls a cigarette, old habit, grins mischievously and lets his words float in the room, a beautiful attic that represents his workshop. Lathes, CAD milling machines, computers and a few hundred kilograms of spare parts cavort on 50 square meters of parquet. Pictures by Marc Chagall hang on the walls in Mediterranean colors, and sunlight falls through huge gable windows. A color mood as can be found in anthroposophical delivery rooms. “May be”, grins Hartman-Wirthwein. “Because this is where my baby, the 125Four, was born.”

Project start

The project will start in March 2007. Dieter designs on the computer every day. Two months later he tears the engine from the China Monkey and dismantles it. “I determine the dimensions and version of the parts on the PC, the final shape is created by trying them out”, says the engine builder, taking a valve wedge between his fingers and turning it like a diamond. The wedge is tiny, ten of which fit on a dime. Hartman-Wirthwein makes most of it itself: camshafts, cylinder blocks, rocker arms, connecting rods and connecting rod rockers ?? The four pistons are connected to the main connecting rod via clever triangular rockers. The middle and outer pistons run parallel. These are original Honda parts. Instead of a 39 mm piston, there are now four 25 mm pistons from a brushcutter. The camshaft is driven by a centrally and openly running toothed belt. Two interrupter cams on the alternator act on two double ignition coils. Most of the components are so delicate that they would not attract attention in a box of Playmobil toys. At most because of their color.

On Good Friday 2008, around a year after the start of the project, the four-cylinder is ready and celebrating its debut on an assembly stand. Dieter did not find a four-carburetor bank that could fit into the chassis. The original carburetor is located differently on an intake port that supplies all four cylinders. His son Fabian holds up a cup of gasoline, which runs through a hose into the carburetor. “I had imagined scenarios…”, says Dieter and grins his mischievous smile as always. “The engine could have blown apart, material defects, incorrect calculation, no lubrication, what do I know. The fact that it starts with the first turn actually surprised me.” Two days later, the four-cylinder is back in the Monkey frame. Four manifolds from the model shop and a racing tailpipe from the VW Beetle guide the exhaust gases from the 125 cubic unit unrestrained into the open.

The first test drive

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Dieter Hartmann-Wirthwein is already planning the next project: “The Monkey is the touchstone for an even more absurd project.”

The parking lot of the supermarket opposite will be the scene of the first test drive on Easter Sunday. Fabian does a few laps, Dieter films and puts the clip on an internet platform. The sound of its small four-cylinder is reminiscent of that of the legendary 750 Four. It is just as huge as the response from the network. Six weeks after the first click, there are dozens of requests for a test drive. “There was even a freak from Western Australia…”, Dieter ponders and pauses briefly. “How I would have loved to see how my 125Four drives”, he says. Wistful, thoughtful. And lowers his gaze. The motorcycle freak is paraplegic from the sixth thoracic vertebra down.

It is March 2, 2002 around 8:30 a.m., a cold morning, a Tuesday. Dieter Hartmann-Wirthwein is on his way to work with his Ducati 900 SS. A path that he always drives. On which he knows every curve, every hump, every pothole, how to negotiate it. He learned route reading during his time as an active racing driver for the Jupo Cup. “Nothing world famous”, he says today, “somehow only places at ten jumped out.” In any case, he gained enough experience. Also on his many tours across Europe. On that morning in March, all experience is of no use. At temperatures around freezing point, the front wheel slips away and Dieter hits the guardrail with his back. A fall that radically changed his life.

“Don’t break them. And: Tell me exactly how high it turns”, he exclaims as his baby rolls off the yard. The small four-cylinder runs whirring and vibrates less than the original. He’s great on the gas and screams his lust out of the beetle pipe. The power output is even. But you have to be careful not to over-rev the engine. At around 8000 rpm it looks tough, but still picks up. The 8000, however, are reached in a flash. Dieter changed the secondary gear ratio from 13 to 40 to 15 to 26 as a precaution. Ultimately, the little monkey could ?? she will now have an estimated six to seven horsepower? be translated a little longer: At around 80 km / h it is over.

Racing motorcycle scented toy

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Tinkerer Dietmar Hartmann-Wirthwein, 51, with his wife Petra, 49, and son Fabian, 21, who started his two-wheeler career at the age of four.

It’s a crude feeling: you’re sitting on a toy, but you can hear and smell a racing motorcycle. Smells Yes, Dieter mixed a shot of Castrol R40 into the gasoline? the oil is biodegradable and is made from castor oil. A chirping, light tone from the head area joins the sweet and sour smell and the buzzing piston instinct. And every time you accelerate again, the filigree self-made parts float in front of the spiritual canvas. Keyword Playmobil. A unique driving experience. Comparable? No. However, the RC 146, built in 1964, was Honda’s first four-cylinder 125cc. 27 hp at 17,000 rpm. Seven gears, 87 kilograms. Luigi Taveri won the world championship with her that year.

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The four-cylinder of the Monkey Four is hardly bigger than a handbag.

It stands ticking Monkey back in the yard. Dieter Hartmann-Wirthwein rolls the tobacco into the paper and grins. A lanky man, type of perpetual student. A man who you see at first sight in the drawer “Draw beer in the crooked, dim half-timbered bar in a university town” would get stuck. He has been taking early retirement since March 2008. His company disposed of it. “Come up with me”, he says, “I want to show you a new project.” As he glides across the floor in his wheelchair, he tells one of his macabre anecdotes that have absolutely nothing to do with the romanticization of immobility: “KTM was recently looking for a 125cc engine designer. Have?? I sent my application, and the answer wasn’t long in coming: Unfortunately, we don’t have any home offices to offer.”

In its charismatic “workshop” Dieter tears a patina-thick cloth from the frame of a 900 Ducati, his accident machine. The engine is still half disassembled. “The monkey was the touchstone”, he says, presents detailed drawings of a new engine and picks up two four-cylinder blocks. “Next year there will be the first Ducati with a V8 engine.” Profile: four 56-cylinder pistons that weigh less than a standard piston. Air-cooled, two-valve, single camshaft, rocker arm, 44 stroke, 868 cubic meters, no desmodromic. Development goal: In the lower speed range, the V8 should power like a two-cylinder, without pounding in the typical way, and turn upwards like crazy. “If the V8 just provides the same performance a little earlier, why should the TuV have something against an entry?” He casts a thousand kilometers out the window, far beyond the parking lot. A sign hangs on the wall: It’s never too late to have a happy childhood.

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