HONDA TRX 400EX TIMING CHAIN Noise Rattle

Cam Chain Tensioner Assembly

The 400EX uses an automatic spring-loaded tensioner that frequently suffers from internal spring fatigue or binding of the worm-gear shaft. When this occurs, it fails to provide sufficient force to the tensioner arm, allowing the timing chain to vibrate or 'slap' against the guides and engine casing. This produces a rhythmic metallic rattle, particularly audible at idle or during deceleration when chain harmonics change.

Cam Chain (Timing Chain)

Over time, the cumulative wear on the pins and bushings of the cam chain links increases the overall length of the chain, commonly referred to as 'stretch.' If the chain exceeds the maximum extension range of the tensioner, the slack will cause a loud rattling sound as the chain impacts the internal engine walls. This is a common high-hour maintenance item for the TRX400EX engine.

SKU: 14401-KCY-671

Exhaust Header Pipe Gasket

The copper crush gaskets at the exhaust port can degrade or flatten, allowing high-pressure exhaust pulses to leak past the flange. These pulses create a sharp, metallic 'clacking' or 'rattling' sound that is frequently misdiagnosed as timing chain noise or valve lash issues. Because the exhaust port is adjacent to the timing chain galley, the acoustics often lead owners to believe the noise is internal.