Hydraulic Tensioner
An oil-pressure-driven plunger device that maintains constant, auto-adjusting tension on a timing belt or timing chain.
A hydraulic tensioner is a device used in timing belt and timing chain systems to maintain the precise amount of tension required to keep the belt or chain tight. It features a spring-loaded plunger backed by a hydraulic chamber supplied with pressurized engine oil.
As the timing belt or chain stretches and vibrates during operation, the hydraulic tensioner automatically extends its plunger to take up the slack, dampening vibrations and preventing the belt or chain from skipping teeth on the sprockets. This automatic adjustment is critical; a loose timing belt can slip, causing catastrophic valve-to-piston contact in interference engines.
If the tensioner leaks its hydraulic fluid or its internal check valve fails, it will lose its damping ability, causing the timing chain to rattle, especially on cold starts. Replacing the hydraulic tensioner is standard practice during timing belt or timing chain replacements to ensure long-term reliability.