Trial Jawa put under the microscope by Gunter Ruttloff

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Trial Jawa by Gunter Ruttloff

Self-made brand chamois trial

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With a lot of skill and the high art of improvisation Gunter Ruttloff conjured up nimble and robust trial chamois from the standard 175 CZ / Jawa. MOTORRAD Classic took a close look at the pre-65 cross-country jumper of the six-time GDR champion.

M.In this story, an could easily use the cliche of disoriented industrial production in the former Eastern Bloc countries when Gunter Ruttloff set to work in the early 1960s. Like so many passionate off-road drivers, the man from Chemnitz from the Euba district had to struggle with the fact that ready-made goods for the competition were either rare and expensive or not available at all.

Trial Jawa by Gunter Ruttloff

Trial chamois brand self-made

Do-it-yourself is the only alternative

As an alternative, the only option was to build it yourself. Some knitted their companions from tamed GS or motocross machines. Others, such as Gunter Ruttloff, were looking for robust and proven large-scale series motorcycles that lost weight with a radical cut and increased handling to the same extent.

But with Flex and a hacksaw alone, a chubby Jawa or structurally identical CZ 175 did not turn into a motorcycle for extreme terrain. If you wanted to win with your own construction, you had to get down to business. And that with all available means. Only the radical modification of the engine brought the desired full punch to, in the truest sense of the word, get out of bed in no time at all.

Strong MZ cylinders at the top, robust Jawa housings at the bottom

Even then, the specialists knew how to deal with the advantages of a lightning-fast, appealing two-stroke engine and to catapult themselves up a steep slope or head-high heel virtually from a standing start. And because there is no substitute for displacement even at such moments, a powerful engine with a displacement of 250 cubic centimeters had to grow out of the sturdy 175 Jawa substructure. With a stroke of 65 millimeters, the MZ 250 cylinder with a 70 mm bore and a smooth but convincing torque curve was sufficient.

Unfortunately, neither the spacing between the studs nor the shape and position of the overflow channels matched. Blessed with access to an aluminum welding machine, Gunter Ruttloff, who was ennobled with a welder’s pass, cut the CZ housing and welded it to the matching MZ counterpart. In order not to have to irreparably destroy an MZ housing for each of his around 60 manufactured EURO engines (made up of EUba and Ruttloff Original), the “crankcase flange” was cast as a single part, machined and grafted onto the CZ housing. A delicate act, not only because of the heat distortion, the vertical separating surface of the Czech case also had to be carefully adjusted and leveled.

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In the classic trial scene, the Ruttloff-Jawa is the marveled exotic among Bultaco, Montesa, Fantic and the like.

The crankshaft and the indestructible four-speed transmission from the CZ, including the cork friction disc clutch, were taken over, only the simplex primary chain was replaced every now and then. The EURO engines used today are being renovated with robust KTM connecting rods and corresponding bearings.

Why didn’t Ruttloff use the complete MZ 250 engine straight away? “The clutch of the MZ was mounted directly on the crankshaft and only worked digitally, so either a frictional connection or none. Allowing it to grind in a controlled manner was impossible for my driving style, ”says the master, justifying the immense conversion effort. In addition, the MZ two-stroke engine was too heavy. And it was missing a fine detail of the CZ claw gear: Here the shift lever, which has been folded up by 90 degrees, also functions as a kick starter. Simply great. Or, to use the words of a current advertising slogan: simply clever.

Ruttloff uses the MZ cylinders built up to 1966

In order to comply with the current regulations for the trial classics built up to 1965 (Pre-65), the Ruttloff-Jawa from owner and classic trialer Norbert Johna has a 24-series carburetor from the Berlin carburetor factory (BVF). Of course, such a tiny cross-section cuts off the top performance of the 250 engine dramatically, but in connection with relatively short control times and the very "slim" exhaust with extremely long, cylindrical manifold, it ensures maximum pulling power from the lowest revs.

And that’s exactly what counts when the classical acrobats maneuver their flyweight pedestals through the tricky sections. For this reason, Gunter Ruttloff relies on the MZ cylinders built up to 1966. After that, the valve timing of the wide-wall cylinders was extended in order to mobilize one or two horsepower for the MZ road models. The wrong way to go for a trial machine. It was ignited either by battery ignition or by the Simson swing-light magnet ignition, which was used from 1970, and always with the classic breaker in both variants.

Only fragments remained of the original Jawa / CZ frame

Like the engine, the series chassis also had to give up tremendously. The steering head with the main frame was retained, but the pipe beams between the front engine mount and the swing arm bearing were cut without replacement. There is now a sturdy aluminum fender that allows the engine block to slip cleanly over stone steps and obstacles. This does not result in any stability problems, especially since the engine with its cylinder head support holds the frame together via a triangular connection. On closer inspection, the original single-tube loop construction mutated into a single-tube bridge frame, the rear end of which was completely removed and replaced by a lightweight rear frame with a deep seat cushion.

At around 4.3 kilograms, the Ruttloff frame makes a significant contribution to saving the weight of the Jawa 250, which weighs just 84 kilograms. In order to achieve the right balance and weight distribution of the trimmer, the designer shortened the new swing arm made of 20 x 2.0 millimeter thick precision steel tubing. Ruttloff left the choice of fork and spring elements to its customers, who in most cases did not buy a complete motorcycle, but only the frame torso with the EURO engine. The rest was pieced together according to budget and availability, which is why Ruttloffs Trialers have all become individual pieces.

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The coupling cable is guided through the cooling fins and a 90-degree deflection via a roller.

In the case of the variant presented by MOTORRAD Classic, an MZ telescopic fork springs in the front and a pair of Rock Shocks struts from England in the aft. The fact that the successful Ruttloff Trialers did not find their way to the West was due, among other things, to the trade ban with NSW countries – that was short for "non-socialist economic areas".

The battle of the systems, then known as the “Cold War”, also fell victim to the international careers of East German off-roaders, who, with the exception of the drivers of the state-sponsored MZ works team, mostly competed against competitors from Eastern Bloc countries. It was not until 1994 that Gunter Ruttloff also won a title in the South German Senior Cup in the West. He is still passionate about and regularly on the classic trial scene.

Technical data Ruttloff-Jawa / EURO

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Slender and weighing just 84 kilograms.

Ruttloff-Jawa / EURO

engine:

  • Single cylinder two-stroke engine with slot control
  • Bore x stroke 70 x 65 mm
  • Compression 7.7: 1
  • Cubic capacity 250 cm³
  • Performance k. AT..
  • 24 BVF carburetor
  • Mixture lubrication 1:70

Power transmission:

  • Multi-disc oil bath clutch
  • Four-speed claw transmission
  • Roller chain

landing gear:

  • Single-tube bridge frame, open at the bottom
  • Double swing arm
  • Oil-dampened Rock Shocks struts
  • MZ telescopic fork in front
  • Wire spoke wheels with aluminum rims
  • Front tires 2.71-21, rear 4.00-18
  • tires with Michelin Competition
  • Simplex drum brakes front and rear

Mass and weight:

  • Wheelbase 1330 mm
  • Dry weight with one liter of fuel 84 kg
  • Tank capacity 4.5 l

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