The Alma Four: Custom Indian/Nimbus Hybrid

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Dutchman Mads Bartholin's Alma Four custom motorcycle made from a Dutch Nimbus frame, Indian Four-style exhaust system and 1,000cc straight-four NSU car engine.
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Owner/builder Mads Bartholin with the Alma Four.
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Engine is an air-cooled 1,000cc OHC four from a 1960s NSU. It manages to look right, thanks in large part to a custom-cast crankcase and bell housing.
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If you didn’t know better, a quick glance at Mads’ Alma Four would leave you believing you’re looking at a late 1920s Indian Four, which of course was precisely the point of the build.

The original Indian Four is a design icon, and in its time it was the largest, most elegant motorcycle to grace the roads. Many attempts have been made to build a modern copy, often using water-cooled car engines, but as far as styling is concerned they all have missed the mark. Except one custom motorcycle, which lives six or seven times zones and an ocean away from where the Indian, ACE and Henderson Four once were brought to life.

Dutchman Mads Bartholin had always wanted an Indian Four, but like most of us, he couldn’t afford one. The ACE and Henderson Fours are just as out of reach, and acquiring something slightly less glamorous, like an Indian Scout, was not an option; Mads was firmly in the “straight four” phase of his life.

Actually, Mads already had a four: a Danish Nimbus. He had rebuilt it with an Indian Four-style exhaust system, a 16-inch rear wheel, a Harley-Davidson solo seat and a wide handlebar. He had even ridden it as far as North Africa a few times. But as much as he liked the Nimbus, he found its 22hp engine too weak. Realizing the futility of tuning the stock 750cc engine he decided to replace it with a 1,000cc straight four from a NSU car. “The NSU engine is air-cooled, inexpensive, looks kind of right and there are loads of them around,” says Mads. This was in 1997.

In the beginning

The first step was to make molds for the Nimbus flywheel/clutch assembly housing that was to be used, and for an engine bottom that would resemble the angular sump of a Nimbus. A local foundry took care of this for a pittance, and after a few tries it looked right. Mads had suspected the car engine would be a bit on the large side for a Nimbus frame, which turned out to be the case. ”It would fit — barely — but there simply wasn’t any room for the gearbox or the gas tank,” he notes, “so it was back to the drawing board.”

As the project progressed, Mads spent many an evening in his basement workshop, beer in hand, carefully studying various 1:1 scale drawings hung up on the wall. Finally, he settled on a version reminiscent of a 1928 Indian. It would lack the comfort of rear suspension and the elegance of the art deco fenders that later Fours came with, and would have the earlier-style frame where the upper backbone ran over the fuel and oil tanks. And it would be a couple of inches longer than its spiritual forefathers, because of a separate, longitudally-mounted gearbox.

Maintaining momentum on this project wasn’t easy, mainly because Mads was studying industrial design at The Royal Academy of Fine Arts and was perennially broke, as students usually are. “Getting married and having two kids took its toll, too,” says Mads, “although thankfully my wife — bless her — had given this project her full support all along the way.” On the other hand, being unemployed part of the time and having an uncanny ability to trade favors with people in the know did help a lot.

Slow and steady

Over the next few years, Mads acquired the sorry remains of an Indian frame, as well as a good number of repro parts including the frame lugs, fenders, the solo seat, a complete leaf-spring front end and the carburetor assembly. Initially, Mads considered using a BMW or Moto Guzzi gearbox, but he soon realized that because of the direction the engine turned he’d end up with a lot of reverse gears. Instead, a Nimbus gearbox with a new Swedish-built four-speed gear cluster found its way to the workshop, along with a Nimbus shaft drive and rear hub assembly. Somewhere along the way the motorcycle was named The Alma Four, “Alma” being Latin for “a particularly beautiful soul.”

Old brochures and factory photographs usually show the Indian Four from the right hand side, where the elegant exhaust system gives the motorcycle a look of moving fast even while parked. In contrast, the left side of Indian Four engines were a mess, cluttered up with the carburetor, the ignition magneto and the generator. Apparently paying homage to the original, this is the case on the Alma Four, too, even if the stock car distributor hides in a slightly neater fashion at the rear end of the overhead camshaft. The Solex carburetor is mated to a modified NSU intake manifold, and a belt drive from the front of the engine spins a Bosch generator.

While the engine came together, a stainless steel four-into-one reverse cone exhaust system was built to be mounted on shortened exhaust stacks. At the same time, an acquaintance rebuilt the frame to match the one-off engine and shaft-drive rear end. This acquaintance, along with many other members of the worldwide Indian motorcycle fraternity, had for years been watching the Alma Four project from the sidelines, helping whenever possible and enthusiastically cheering Mads on. It was now 2002.

Once back from the welder, the frame was placed on the workbench and the engine dropped in. Wheels to match the large 4.5 x 18in Cheng Shin tires were laced with stainless steel spokes. Copper oil lines were soldered, and cloth-covered wiring for the simple electrics slowly, but steadily, transformed the dream to an actual motorcycle. In 2003 it was started up for the first time.

The twin fuel tanks had to be designed and built from scratch, because the overhead cam NSU engine was much taller than an original engine from Springfield. This was a bit of a problem, as Mads wanted to keep the low look of the bike.

Like the flywheel housing and the final engine sump, which now was much more ribbed and rounded than the previous two versions, the tanks were cast in aluminum. On the outside they look like stock tanks, but their hidden sides are shaped to accommodate the NSU engine’s large cam chain housing and overhead camshaft, and to clear the engine’s individual valve covers.

Details, details

Lots of other work remained to be done, of course. Cutting the threads for the fuel caps was one detail. Welding a bracket for the stock headlamp — found ridiculously cheap at a regular flea market — to resemble a cast item, was another. Small things like filing the rear fender bolt heads to half their height were but one of the dozens of details needed to make it look just right. Whoever designed the fours back in the 1920s was good at it, and Mads, now officially an industrial designer, was determined to do at least as well.

In 2005 the Alma Four was once more prepared to run under its own power. After a successful trial run the bike was disassembled. Parts were powder coated black and final detailing executed, and it went on its maiden voyage in a late spring snow storm in 2006. Serious road testing over the summer revealed no problems at all, save for a bit of dirt in the carburetor. “The engine starts first kick, pulls strong, and the bike is steady like any other old 1920s large hard tail, at least up to the 100mph I’ve taken it so far,” Mads claims. Braking the quarter-ton behemoth from high speed is, on the other hand, a different matter, as the performance of the Nimbus and Indian drum brakes is limited.

This particular engine makes about 40hp in its stock configuration. “The engine is over-engineered, and the Alma Four weighs about one-quarter of the car it came from, so reliability is not an issue. Should something undesirable happen to it anyway, it’s a fair guess that NSU parts will be cheaper than those for an Indian,” Mads says.

Priceless outcome

Mads is satisfied with the final result, even if his limited finances forced a few compromises along the way. ”The front end is a repro Scout item, but a Chief version would have looked better,” he thinks, “and a real paint job would have been nice too.” But these are minor niggles. Unsurprisingly, even vintage bike purists give it a nod of approval, recognizing that no Indian parts were harmed to make this motorcycle.

In hindsight, was it worth spending all those hours building something looking very much a 1928 Four? Instead of, say, working about the same number of hours in a regular job, and buying an original old American Four for the money? Mads doesn’t hesitate: “Definitely, if not for its value — which probably is on par with a 70-80 year old four anyway —  then certainly for being able to ride a unique and comparatively much more reliable motorcycle.”

One might add that the experience Mads gained by designing and building a motorcycle almost from ground up is priceless. It will come in handy for the overhead valve Super X Hill Climber now on his workbench. MC

Read more about the motorcycles mentioned in this article: 
1917 Henderson Special Model G 

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