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- Pure recklessness
- Interview Peter Johansson (ex-Yamaha works rider) – "That’s how a four-stroke must be"
- Technical specifications
Presentation of the KTM 400/520 SX
Pure recklessness
Slim line – the new sports four-stroke from KTM is supposed to scare the competition with its low weight and nimble handling.
Saturday, February 22, 1997. Dense clusters of journalists and photographers surround the brand-new Moto Cross factory machine YZM 400 F from Yamaha in the paddock of the season opener classic in Beaucaire, southern France. The reason for the buoyancy: With a four-stroke engine of just 400 cm³ in the slim chassis of a quarter-liter two-stroke crosser, Yamaha is in a way proclaiming the technical bridge between the lively, handy two-stroke crosser and the high-traction, low-emission four-stroke off-road motorcycle. Quasi the egg-laying woolly milk sow in the rough trade. In the same year, the new design under the works drivers Andrea Bartolini and Peter Johansson, with six victories in the half-liter GP, proves the fundamental consistency of the concept.
At the same time as the presentation of the new Yamaha, the lights in the development department at KTM also go out later and later. Because the well-engineered and durable universal propellant of the Austrian four-stroke model range, the legendary LC4 engine, has long since gone to waste – at least as far as the highly specialized motocross sport is concerned – with its high weight and lush dimensions. A new, sports-oriented unit was needed. “Of course, the Yamaha 400 inspired us, but our engine should have the option of variants with more displacement from the start,” said Development Manager Wolfgang Felber, who brought insider knowledge and economic thinking into play right from the start. Because while amateur off-roaders are happy with the easy-to-drive 400cc Yamaha, which has been on sale since the beginning of last year, the faster-paced clientele (see interview with Peter Johansson on page 202) criticize the small four-stroke engine’s insufficient power reserves. Especially since from a commercial point of view, the new design by KTM also had to cover the two large four-stroke classes of enduro competitions (up to 400 cm³ and over 500 cm³).
Also in Beaucaire and exactly two years to the day after the Yamaha debut, the Austrian answer to the trendsetter from the Far East that has become metal and plastic is rolling behind the gate: the KTM 520 SX, the vanguard of the new light crossers and enduros from KTM, which both with 520 as well as with 400 cm³ displacement are supposed to turn the off-road market upside down. Indeed, the SX cannot deny its role model. The chassis comes almost unchanged from the current quarter-liter two-stroke colleague. Only the frame front pipe has to fork into the joists earlier because of the higher exhaust manifold in four-stroke engines.
The simple solution to the chassis question first and foremost requires a motor that is minimized in size. Nevertheless, the 400cc KTM version is not content with the low stroke of the Yamaha of 60 millimeters, which is decisive for low overall height and easy turning. Instead, the KTM piston whizzes up and down 64 millimeters. Combined with a 89 millimeter bore, this results in a displacement of 398 cm³. 72 by 95 millimeters inflate the big sister to 510 cm³. The question of the power – MOTORRAD measured 50 HP at 7800 revs on the Yamaha – is answered in the 400 with 48 HP at 8500 revs, while the 520 proclaims a moderate 56 HP at 7500 revs. In order to keep the rotating masses as small as possible because of the maneuverability, the KTM technicians used a simple but effective trick. The centrifugal forces, which are already relatively low due to a small and light crankshaft, are partially eliminated by a relatively large counter-rotating balance shaft. As with the four-stroke models from Husqvarna and Husaberg, the KTM’s crankshaft also runs in a crankcase that is separate from the gearbox in order to avoid splashing losses.
In contrast to the dry sump lubrication from Yamaha, whose oil is stored in the frame front tube, KTM relies on a weight-saving wet sump lubrication with an oil pump. A single liter of oil in the engine housing (Yamaha: 2.5 liters) including the missing supply lines from the frame save a good two kilograms in weight. KTM does not accept doubts about the thermal load capacity – test engines ran for more than 130 hours without defects.
In addition, the pound sterling of fruits shows: At 28.5 kilograms, the new KTM engine weighs barely more than the 26-kilogram quarter-liter two-stroke engine, an impressive 8.5 kilograms less than the LC4 unit, and above all is? Kilograms slimmer than the Yamaha competitor.
It has to, after all, KTM wants to set new standards with the announced lightweight crossers of 105 kilograms (Yamaha: 112 kilograms) and enduro bikes of 115 kilograms.
On the transmission side, the modular principle prevails. The Moto Cross version has to get by with four gears, two further gear sets extend the cross transmission to the six-speed gearbox of the Enduro. Whereby the Kickstarter should become largely unemployed in the foreseeable future, because all enduros are basically equipped with electric starters. Parallel to the six Moto Cross factory machines, a pilot series of at least 80 competition enduros is to be built in April. The results from five months of practical tests will then flow into the final machine before the start of series production in September. A second oil filter and a larger water pump are already planned in any case.
I.KTM would like to bring 3200 machines to the off-road crowd for the 2000 season. Whether it succeeds depends on the results of Messrs. King, Johansson and Co. – at the race premiere in Beaucaire, Johansson only came fifth in the first of the three races – to a large extent on whether it is KTM in both displacement versions succeeds in achieving the playful ease of four-stroke existence on the Yamaha.
Interview Peter Johansson (ex-Yamaha works rider) – "That’s how a four-stroke must be"
? In 1996 you finished third in the World Championship on the 630 four-stroke Husqvarna. After that, over the past two years you have seen the development of the Yamaha 400cc factory machine up close. After switching to the 520 KTM, you have an overview of all displacement concepts. What are the differences in driving behavior? The Husky is the traditional four-stroke machine. Conventional chassis, powerful engine. Good-natured, but a little sluggish. Basically, the Yamaha drives like a two-stroke motorcycle. It must be kept constant at speed. But it is very handy. The 520 KTM is the golden mean. The power comes from the lower speed range. This ensures plenty of traction and less hectic driving. With the KTM I only have to shift gears half as often as with the Yamaha. That’s how a four-stroke must be. ? The concept of the Yamaha as a trend-setting motorcycle is clearly based on the advantage of the low rotating masses, which make the machine superior in handling. Can the KTM as a 520 keep up in this respect? I think so, because the engine is only part of the new overall concept. Like Yamaha, KTM largely uses the slim, agile 250 chassis. Its part in the improved handiness should not be underestimated. Wouldn’t it still be interesting to test the 400 cc version of the new KTM engine? No, 400 cc is not enough to keep up with the front runners in the World Championship. The biggest problem is the starts. There, the large four-stroke engines and the half-liter two-stroke engines simply move away. ? In your opinion, does Yamaha even have a chance of winning the world title with the 400?.
Technical specifications
Technical data: Engine: water-cooled single-cylinder four-stroke engine, a balance shaft, an overhead, chain-driven camshaft, four valves, wet sump lubrication. Bore x stroke 89 x 64 mm (420 SX) / 95 x 72 mm (520 SX) displacement 398 / 510.4 cm³ Nominal output: 35 kW (48 PS) at 8500 rpm (400 SX) 41 kW (56 PS) at 7500 rpm (520 SX) Max. Torque: 43 Nm (4.3 kpm) at 6500 / min (400 SX) 51 Nm (5.1 kpm) at 6250 / min (520 SX) Power transmission: primary drive via gears, hydraulically operated multi-disc oil bath clutch, six-speed gearbox (Enduro) , Four-speed gearbox (Moto Cross). Chassis: single-loop tubular frame with split beams, upside-down telescopic fork, guide tube diameter 48 mm, two-arm swing arm made of aluminum profiles, central spring strut directly articulated, disc brake in front, 0 260 mm, disc brake in rear, 0 220 mm, tires 80 / 100-21 in front , 110 / 90-19 rear Chassis data: wheelbase 1481 mm, steering head angle 63.5 degrees, caster 115 mm, spring travel f / r 300/340 mm Dimensions and weights Seat height 925 mm Empty weight 105 kg (Moto Cross version), 115 kg (Enduro version)
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