Technical Modifications for 2003

SX / EXC / SPORTMINI

2-Stroke and 4-Stroke

Updates on 2003 Models: SX, EXC

125/200 Engine

The world champion engine (125 SX) and the highly popular 200 EXC engine are widely considered as the best in their class.

For the year 2003, these engines were optimized in numerous details and spiced up with upgrades taken straight from the racing scene.

As an ideal complement, a 200 SX model will be launched in the 2003 range: its weight and handling correspond to that of a 125 SX, its engine power almost reaches that of the 250cc motocross bikes of other manufacturers. The KTM 200 SX is the ideal funbike for amateur motocrossers, vets, or a professional race machine for those who want to move on up from the 125cc class.

Transmission 125/200

Factoring the aspects of constantly increasing engine performance of recent models, the new 125/200 transmission now comes with a new, wider and thus more load-resistant 2^nd gear.

The transmission of the 125 SX has been reduced from 6 gears to 5. With the enormous performance potential 5 gears are now more than plenty. This has also subsequently reduced the weight, as was done on the 125 GP bike.

Gearshift Mechanism 125/200

A new aluminum gear selector drum having narrower shift grooves permits an even smoother shifting operation, especially in extreme-load situations (powershift). In addition, a new bearing roller of the gearshift fork helps minimize wear.

Crank gear/Piston 200

All 200cc models are given a new crankshaft for improved balancing and reduced inertia weight. The result is the reduction of vibrations and weight as well as a quicker throttle response.

The 200 SX is provided with a lighter, easier revving single-ring piston particularly suited to motocross.

Cylinder 200

A new molded silicone ring supersedes the paper seal to provide ideal sealing for the 200cc cylinder head. The combustion chamber in the cylinder head was given a new shape and the transfer ducts were modified in a new casting mold for optimum power yield.

Exhaust Control System 200 SX

Inherited from the 125 SX and adapted, the centrifugal unit provides the 200 SX with peak power and characteristic needed for motocross.

Carburetor 200 SX

The same PWK 39 carburetor used with success on the 125 SX is employed on the 200 SX to feed the fuel/air to the 200cc engine.

Exhaust 200 SX

An exhaust expansion chamber developed in motorsports for this specific model makes full use of the engine potential of the new 200cc bike.

NEW DESIGN: 250 SX

The 250 SX 2003 is a completely redesigned bike, from the engine to the frame:

To create a bike with the potential to win Grand Prix races in the 250cc World Championship Series, the design of the 250 SX received multiple technical innovations, which were immediately implemented into the production bike series for the year 2003. This clearly documents KTM’s “ready-to-race” philosophy: having been used in professional GrandPrix racing for only one year, the factory technology of the new bike is already made available to customers.

Technical background:

The positioning of the crankshaft axle in relation to the vehicle’s center of gravity has been shifted in order to improve handling. The cylinder angle has also been modified so that the cylinder is now positioned almost vertically to the motorbike’s longitudinal axis, again another subtle handling improvement. This also makes engine dimensions more compact and the frame shorter. By rigorously cutting the weight of engine components, we created probably the lightest and most compact engine in its class. The new engine along with the new chassis work in tandem to greatly improve handling.

250 SX Engine

Housing

With a focus on weight reduction, the ignition, outer clutch and control covers are all made of magnesium. The Boyesen diaphragm housing introduced on last year’s model has been improved for the new engine.

Transmission

A fully re-dimensioned 5-speed transmission, slimmer and more compact, helps save weight and space.

Gearshift

A new aluminum gear selector drum with narrower shift grooves makes switching operations even smoother, especially under extreme loads. Plus, a new bearing roller of the gearshift fork minimizes wear and friction.

Clutch

The entire clutch works has been made lighter and slimmer. The forged and milled clutch wheel was radically modified to reduce moving masses.

Crank gear/Piston 250 SX

Thanks to a new plastic insert and a slightly lower inertia weight, the new SX crankshaft is 100 grams lighter in weight, which improves the engine’s response and power development.

By using a shorter connecting rod, with the bore/stroke ratio staying the same, the cylinder is now shorter and lighter. The piston is lighter as well.

Cylinder

Having a new basic shape, the shorter cylinder features a re-dimensioned exhaust duct. The much lighter intermediate flange also has a new, improved exhaust seal.

Ignition/Carburetor

The Keihin PWK 38AG carburetor comes with a new electronics box and a optimized ignition curve.

Kick starter

Additional weight savings come from a new, lighter kick-start lever and lighter weight kick start system (borrowed from KTM’s 4-stroke racing bikes)

250/300 EXC Engine

A new exhaust shape in the cylinder prolongs the useful life of the piston rings and a redesigned combustion chamber in the cylinder head improves performance characteristic at and peak power.

250/450/525 Racing Engine

GENERAL INFORMATION

For 2003 the 400cc models are, in line with the new rules, enlarged to a displacement of 450cc.

The motocross versions as well as the 250 EXC engine were modified, especially with regard to achieving higher peak r.p.m. levels.

The EXC models are equipped with both electric starter and kick-starter.

On all models, the weight of the outer clutch hub has been reduced by 100 grams.

The fixed screw connection between the driver and the transmission shaft allows an even more precise functioning of the clutch. New spark plugs having a modified socket contact (12 mm) will in the future reduce the likelihood of contact malfunction with the socket. An improved cover for the actuation of the accelerator pump keeps out dirt and prevents malfunction.

The transition from a sand-cast to a die cast case has allowed us reduce the weight of all three engines.

250 EXC Racing 4-Stroke

A new cylinder head, whose port cross-section has been increased from 35 to 37 mm, and a new Keihin FCR-MX 37 carburetor, as well as lighter valve springs boost the r.p.m. level as well as peak power.

450 EXC Racing 4-Stroke

This engine is based on the 2002 400cc racing engine. The bore of the world champion 400cc engine from 2001 was maintained while its stroke was increased from 46 to 72 mm.

450 SX Racing 4-Stroke

KTM’s goal for this model was to develop a 2003 450cc 4stroke with the performance of our 2002 520cc bike.

Transmission

A modified 4-speed transmission that has already been used in the 520 SX saves weight and accommodates the increased power of the 450cc engine.

Crank gear/Piston

A new short-stroke-type bore/stroke ratio of 95: 63,4 was designed.

Due to its reduced inertia weight and the lighter balancer shaft, the extremely lightweight new 450 SX crankshaft has a lower weight, which significantly improves the engine’s response and power development. A new Lightweight connecting rod contributes to these improvements.

Cylinder/Cylinder Head

A new cylinder head, whose port cross-section has been increased from 39 to 41 mm, and a new Keihin FCR-MX 41 carburetor with hot-start knob, plus lighter valve springs increase peak power and reduce the oscillating masses.

In conjunction with re-designed camshaft profiles, extremely lightweight titanium valves increase performance over the whole power band. At the outlet end, a chromium-plated single-pipe exhaust features a new, lighter motocross main silencer.

525 SX Racing 4-Stroke

Extensive efforts have boosted the performance level of this engine.

Crank gear

Featuring a slimmed-down inertia weight, the new 525 SX crankshaft is about 800 grams lighter.

Cylinder/Cylinder Head

A new cylinder head, whose port cross-section was increased from 39 to 41 mm, and a new Keihin FCR-MX 41 carburetor with hot-start knob, as well as lighter valve springs improve peak power.

Through a change in timing, the modified camshaft boosts peak power and increases the maximum r.p.m. .

Ignition System

New digital control electronics and a lighter weight ignition system deliver improved throttle response.

SX / EXC all Displacements: Chassis Modifications

Chassis innovations on all models have their focus on improved handling.

With many general improvements on all models, the chassis of the newly designed 250 SX was the object of the most intense upgrades.

General Improvements

Fork

In 2003, all SX and EXC models will come with the White Power USD 48 mm forks.

All motocross models will be equipped with a pre-load adjuster. This means: the spring preload can be readjusted fast and easily on the outside.

The new fork has now three bearings per fork tube, which ensures a better guidance of the inner tubes during compression travel. KTM also improved chromium quality of the fork coating to prevent excessive “pumping up“ of the fork in use.

The offset of the fork plates on the SX models in relation to the steering head was changed by 14 mm for quicker steering.

Shock Absorber

The WP PDS suspension strut was modified considerably. A bigger compensating tank and a larger oil volume prevent premature fading. Changed flow cross-sections for the oil stream and new tuning setups provide better progression.

Axle/Hub

All SX and EXC models come with a new front-wheel axle enlarged from 20 to 26 mm.

The front-wheel hub was also given a new design and its diameter increased from 36 to 52 mm.

The rear-wheel hub was also reinforced from 48 to 64 mm.

Handlebar/Footrest/Frame rear end

All SX and 2-stroke EXC models come with a high quality conified Renthal handlebar, all 4-stroke EXC models with a 12mm Magura handlebar of identical design. The rear frame of the 125SX is 5mm lower and the position of the footrests was moved up by 3 mm. All 2003 EXC models will be fitted with the broader footrests of the SX machines.

Clutch Hose

To prevent damage all models are fitted with flexible steel clutch hoses.

Rear Brake Caliper

All 125, 200 and 525 SX models are equipped with a rear-brake caliper piston diameter reduced from 28 to 26 mm.

The model 450 SX comes with a completely new caliper, whose weight was reduced by about 250 g, and with a piston diameter of 26 mm.

Tank/Spoiler

All EXC models boast a new tank with the “SX“ look. Also the shape of the tank shrouds is made uniform for both models. The advantage for the Enduro models is a more ergonomic tank/seat contour and thus a better sitting position. All tanks come in a basic orange with the EXC models slightly transparent. The EXC tanks are equipped with new fuel cocks. A recess in the tank allows riders to operate the choke and warm start knob with easily.

Speedometer

The Enduro models come with a highly functional digital speedometer with a control unit which, as an option, can be arranged away from the speedometer at the end of the handlebar.

Plastic Components

The new series look for 2003 is taken from KTM’s title winning 2002 GP Team.

The models 200, 250 and 450 SX are given a new one-piece rear end, which integrates the side paneling for a slimmer and more ergonomic feel without connecting joints. New quick-release pushbuttons facilitate the mounting and dismounting of the air-filter box cover on these models.

All SX models are fitted with a new modified front race number plate with integrated brake hose guide. A full-width radiator guard (on the 4-stroke racing KTM’s) provides for optimum air guidance and efficient cooling. A new, seamless seat cover creates an ideal surface.

Graphics Design/Colors

In 2003 the rear mudguard and the side paneling are orange, the shrouds, lamp mask, and the front mudguard is also orange. The seat is all black.

The KTM shroud logo was given a new design so as to cover the entire shroud.

The frame and the hubs are power-coated in a gold hue, matching the color of the fork.

NEW DESIGN: 250 SX CHASSIS

Frame/Swinging Fork

To fit with the compact new engine and the upright cylinder, the new frame of the 250 SX has been shortened by 15 mm for a shorter wheelbase and improved handling. New steering-head gusset plates, various forged components, and a reinforced swing-arm bolt contribute to the frame’s enhanced stiffness.

As a result of the shorter frame, a 10-mm longer swing-arm was mounted on the bike.

Brake System

The new foot-brake cylinder is equipped with an integrated compensating tank. A specially developed diaphragm handles pressure compensation. By using a refined pressure transmission system, the internal pressure can be kept at moderate levels to avoid overheating.

The design of a torsionally stiff, forged footbrake lever with a new ball bearing has been adapted to the slim general appearance of the new frame.

Model Updates for 2003: SPORTMINI

All Mini models match the color and graphics design of the 2003 SX models.

Mini AC Series (air-cooled):

50 Mini Adventure / 50 Junior Adventure / 50 Senior Adventure

The 50 Mini Adventure for 2003 now comes with an external oil tank and oil pump.

All Mini models come with a new, more wear-resistant steering-head bearing. The 14-mm carburetor has been replaced by a 12-mm carburetor.

In addition to the new Mini LC (water-cooled) models, the Mini ACs (air-cooled) are available as economical beginners‘ bikes under the “Mini Adventures“ label.

50 SX Pro Junior LC / 50 SX Pro Senior LC (water-cooled)

For even better handling, the popular Pro Senior LC race bike now features 12-inch rims instead of the former 10-inch rims.

Both models come with new, more wear-resistant steering-head bearings, the Pro Senior model with a tapered roller bearing.

The combustion chamber in the cylinder head was given a new shape and the transfer ducts were modified to improve performance.

65 SX

To use the maximum displacement for its class, the stroke grew from 40 to 40,8 mm and a displacement of 64,85 ccm.

An aluminum kick-starter instead of the former steel lever saves weight and a new joint makes it easier to operate.

To save weight, the ignition cover is made of aluminum. The 65 SX is now equipped with a state-of-the-art digital ignition.