2007 KTM 450SX-F

2007 KTM 450 SX-F: KTM Reinvents Its Open-Class Motocrosser

The 2007 KTM 450 SX-F was a major redesign and effectively a new generation of KTM four-stroke motocross bike. The previous 450 SX used KTM's older RFS-based engine architecture, but the 2007 SX-F arrived with an entirely new 449.3 cc DOHC engine, a new chassis, revised WP suspension and one of the model's most memorable features: electric starting with no kickstarter.

The new engine used a 97.0 mm bore and 60.8 mm stroke with a 12.5:1 compression ratio. Four lightweight titanium valves were operated by twin overhead camshafts through finger followers, creating a much more compact and high-revving design than the older RFS engine. KTM paired it with a Keihin FCR-MX 41 mm accelerator-pump carburettor, and owners maintaining these early carburetted SX-F models can compare replacement options through the MXOwners carburettor reference.

Another unusual feature was the four-speed gearbox. While most contemporary 450 motocross bikes used five-speed transmissions, KTM chose four relatively broad ratios to suit the strong torque of the new engine. A hydraulically operated wet multi-disc clutch continued KTM's established approach, while the standard final gearing used a 14-tooth countershaft sprocket and 52-tooth rear sprocket.

Electric starting was the feature that attracted the most attention. The 2007 450 SX-F had no conventional kickstarter at all, making KTM one of the first manufacturers to commit fully to push-button starting on a serious production motocross bike. At the time this was considered a bold move because batteries and starter motors added weight, but the convenience of instant restarting after a stall quickly demonstrated its value.

The chassis was equally new. KTM developed a revised chrome-molybdenum steel frame with larger oval-section tubes, redesigned bodywork and a new cast aluminium swingarm. The riding position was also reshaped to give the rider better contact with the motorcycle while standing or moving forward in corners. This helped separate the SX-F from the older KTM four-strokes, which had retained more obvious enduro-bike influences.

Suspension consisted of a WP 4860 CC MA 48 mm closed-cartridge fork offering 300 mm of travel and a WP PDS 5018 rear shock providing 335 mm. KTM retained its distinctive linkless PDS system rather than adopting a conventional linkage. Correct setup remains especially important on these early SX-F machines, and the MXOwners fork oil reference is useful when servicing the closed-cartridge WP fork. The MXOwners rear suspension reference can also help owners identify and understand the PDS arrangement.

The new engine used pressure-circulation lubrication with three oil pumps, with the engine and four-speed gearbox sharing approximately 1.3 litres of oil. Regular oil and filter changes, valve-clearance checks and careful air-filter maintenance were essential because the 450 SX-F was designed as a high-output competition machine rather than a low-maintenance trail bike.

Historically, the 2007 450 SX-F was one of KTM's most important motocross models. It replaced the company's earlier-generation four-stroke concept with a purpose-built modern MX platform and introduced electric starting as a genuine performance feature rather than a convenience reserved for enduro bikes. The basic direction established here - compact DOHC engine, electric start, steel chassis, hydraulic clutch and high-spec WP suspension - would influence KTM's 450 motocross machines for years to come.