2012 NEW MOTOCROSS BIKE BUYERS GUIDE: THE 2012 KTM 450EXC ISN’T A MX BIKE, BUT IT DOES HAVE A FUEL-INJECTED, SIX-POUND LIGHTER, KTM 450 ENGINE

450 ENGINE: Compared to the predecessors, the new 450EXC engine generation features a brand-new design. Due to improved packaging, the dimensions of the engine cases are drastically reduced (a major advantage of the smaller cases is the higher ground clearance because the frame tubes can be higher without raising the seat and gas tank). The counterbalancer is no longer in the center of the engine. It has been moved to the side and doubles as the water pump shaft. The engine cases are now die-cast instead of sand-cast. This allows the wall thicknesses to be much thinner to save weight?without reducing strength. A special high-strength aluminum alloy is used in the cases to guarantee higher ductility. In order to make the engine more user-friendly, the new generation 450 features one common oil circuit. The new engine design results in an amazing weight reduction of 2.5 kilograms (just under six pounds) compared to last year’s 450 engine. Most EFI engines typically get heavier because of the magneto system and fuel pump being added, but KTM’s already have a battery to power the electric starter, so they don’t need the KX-F, RM-Z, CRF or YZ-F style magneto (plus KTM’s fuel pump is half the size of the units used in Japanese brand machines). The EXC engines will come with kickstarters and electric starters.

COUNTERBALANCER/IMPELLER: Due to improved materials and the creative design, KTM’s engineers managed to reduce the oscillating masses in the 450 engine drastically (15 percent on the 450 engine and 20 percent on the bigger 500EXC engine?actually a 510). This allowed KTM to use a counterbalancer that is over one pound lighter than last year. The counterbalancer and the water pump impeller share the same shaft and are located in a much sleeker side case.

CLUTCH: A new one-piece clutch basket combined with the primary gear is made of high-strength billet steel (look closely at the primary gear). The steel basket, of which a version was used on the KTM 350SXF last year, guarantees improved reliability and, because it is stronger, it can be made smaller to allow the KTM designers to make the engine narrower. Another plus is that the 2012 clutch is rivetless and 6.5mm narrower. KTM will also switch the clutches on its four-stroke engines to a Bellevile (diaphragm) washer-style spring. The use of the Belleville washer allowed KTM’s designers to add a rubber damping system guaranteeing more transmission reliability. Clutch actuation is still hydraulic (Brembo).

OIL PUMPS: The latest KTM 450EXC engine family features a newly designed oil circuit with two instead of three oil pumps and only one common oil circuit. The pressure pump lubricates the con-rod bearing, balancer shaft, valve train and supplies oil for piston cooling. The suction pump evacuates the crankcase from blow-by and oil, also lubricating the clutch and the transmission.

450EXC EFI: The Keihin electronic fuel injection (EFI) uses a 42mm throttle body in the 2012 450EXC model (we know that the 450SXF will remain carbureted for 2012). There is optional map selector switch for the ignition timing and EFI software for reprogramming the fuel maps.
 
CRANKSHAFT: KTM will install an ultra-light connecting rod in the 2012 450 engines (using high-grade Pankl steel alloy). The piston is also lighter?as is the new electric starter motor.

CYLINDER HEAD: All ports and the combustion chamber have been redesigned in the single overhead cam cylinder head. The new camshaft actuates four valves via lightweight finger follower-style rocker arms, with high-quality titanium valves on the intake side.

2012 KTM 450EXC.

Photos: H. Mitterbauer & Erlmoser Marcus