2003 KTM SX model updates

1 of 1

200 SX Engine

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, veterans, or a professional race machine for those who want to move on up from the 125cc class.

Numerous details were optimized and improved in the 2003 engines that were taken directly from the professional race circuit.


Factoring the aspects of constantly increasing engine performance of recent models, the new 200 SX 6 gear transmission now comes with a new, wider and thus more load-resistant 2nd gear.

Gearshift Mechanism

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

The 200 SX is 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.


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

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


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


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


The 250 SX 2003 is a completely redesigned bike, everything 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 demonstrates 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.

The total engine weight saved in comparison to its predecessor is over 3 kg.

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 results in more compact engine dimensions and a shorter frame. 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


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.


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


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


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

Crank gear/Piston

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 and optimized as well.


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.

The vastly weight reduced cylinder head is constructed with a new combustion chamber.


The Keihin PWK 38S 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)

450 SX Racing Engine


The successful world championship engine generation was totally revamped.

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

KTM’s goal for this model was to develop a 2003 450cc 4stroke with the performance of our 2002 520cc bike, especially with regard to achieving higher peak r.p.m. levels.

The total engine weight saved in comparison to its predecessor, the 400 SX Racing, is 1.5 kg.


The transition from a sand-cast to a die cast case has allowed us reduce the weight by around ½ kg.


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.

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.

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 is lighter by 0.8 kg, which significantly improves the engine’s response and power development. To specifically adapt the engine characteristics, 500 g of inertia weight is removable or can be adjusted with supplementary weight. A new lightweight connecting rod contributes to these improvements.

Carburetor/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 reduced the total weight of the cylinder. An improved cover for the actuation of the accelerator pump keeps out dirt and prevents malfunction.

In conjunction with the adapted camshaft profiles, conical valve springs and extremely lightweight Del West 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.


New spark plugs having a modified socket contact (12 mm) will in the future reduce the likelihood of contact malfunction with the socket.

200 SX / 250 SX / 450 SX Racing: Chassis Modifications:

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

General Improvements


In 2003, all SX models will come with the White Power USD 48 mm forks and pre-load adjuster. This means: the spring preload can be readjusted fast and easily on the outside.

The new fork has now three sliding bushes 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 new settings correspond to those optimized during tests done by our factory riders.

The 200/250 SX model’s offset of the triple clamps in relation to the steering head was reduced to 14 mm (like the 125 SX), allowing for quicker steering and more pressure on the front wheel.

Shock Absorber:

The new WP PDS suspension strut, based on the race circuit, 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.


All SX and EXC models come with a new front-wheel axle enlarged from 20 to 26 mm, improving stability, rigidity and allowing for more accurate turning.

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.

Clutch Hose

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

Rear Brake Caliper

The 250 SX and 450 SX models are equipped with a brand new rear brake caliper, which is 250 g lighter, and a 26 mm piston diameter.

The 200 SX receives the reduced piston diameter, 28 to 26 mm, of the rear brake caliper from the 125 SX bike.


All tanks come in a basic orange. A recess in the tank allows riders to operate the choke and warm start knob comfortably (450 SX Racing).

Plastic Components

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

The models 200, 250 and 450 SX are given a new one-piece rear end with a new, lowered aluminium sub frame, which integrates the side paneling for a slimmer and more ergonomic feel without connecting joints. A new air box with increased volume provides even better power output. New quick-release pushbuttons facilitate the mounting and dismounting of the air-filter box cover on these models.

All models come with a newly designed front wheel fender for improved splash protection and 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, race number plate 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 and the handlebar.


In addition to the above mentioned modifications, the 250 SX also received these following changes:

Frame/Swing Arm

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, similar to the factory bikes, was mounted on the bike.

Brake System

The rear brake is drawn from the latest technological concept:

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.

MCN Staff

By MCN Staff