ASK THE MXPERTS: MY 2009 KTM 250SXF HAS A DEATH RATTLE

The long cam chain needs to be tensioned to keep it from jumping a tooth on the camshaft or coming detached—either was it causes a lot of damage. The chain tensioner keeps it tight

Dear MXA,
My well-used-but-never-abused KTM 250SXF has a really bad top-end rattle. It is scary. When I start the bike, it sounds like the piston is banging off of something. The noise lasts for 15 seconds and then disappears. My buddy says that I need to check the valve clearance. Is it the valves?

No. Your cam chain tensioner is the cause of the noise. KTM’s 250SXF engines, starting in 2008, used a hydraulic cam chain tensioner. This design is dependent on the hydraulic pressure developing enough force to pump oil to activate the chain tensioner. Once the hydraulic pressure is built up, which, not coincidentally, takes about 15 seconds, the slapping cam chain noise goes away. You can, however, install a Dirt Tricks KTM cam chain tensioner to eliminate the noise. It captures oil pressure and combines it with a mechanical ratcheting system and cam chain spring to keep the chain properly tensioned. The Dirt Tricks cam chain tensioner retails for $89 at www.dirttricks.com.

 

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