Next time you work with a drive belt, timing belt, or timing chain, you’ll likely have to loosen a tensioner pulley to remove it. Following these general recommendations and specific instructions from your owners manual or restoration manual, your belt or chain will function for the life span of your car.

Toyota and additional timing belt tensioners are loosened by simply removing them from the engine. You need to slowly compress them in a bench vice and lock them with a pull-pin before reinstallation.
Hydraulic (not hydraulic-damped) tensioners are almost always situated in the timing case, mostly upon vehicles with timing chains, though some are used in combination with timing belts. Hydraulic tensioners are driven by essential oil pressure from the engine oil pump and may press on a tensioner pulley (timing belts) or tension slipper (timing chain). You’ll likely need the year, make, and model details, and you may have to use special tools for this type of tensioner pulley.
Typically, a hydraulic tensioner needs to be “reset” and locked after removing it from the engine. Remove the lock only after the tensioner, pulley, or slipper, and timing belt or timing chain are installed and aligned.

The spring maintains tension, as the hydraulic damper keeps it from bouncing under load changes. This prevents timing belts and timing chains slapping and jumping the teeth and continues drive belts from slipping and making noise. To loosen a drive belt spring tensioner pulley, refer first to the repair manual or owners manual’s specific calendar year, make, and model information.
You may need a special tool, but many spring tensioners have a square hole, car pulley belt201909231201352347633for a 3/8” or 1/2” breaker bar, or a hex or square protrusion for a wrench or socket. Using the correct tool, release tension on the belt. You’ll need to hold some spring tensioners while slipping on a new belt. Others may have a locking mechanism, such as a hole for a locking pin or hex crucial.

To loosen an NAI tensioner, loosen the locking nut or bolt, then back off the tensioner screw. Drive the pulley toward the other pulleys or accessories, loosening the belt.
Spring tensioner pulleys, as the name implies, make use of a spring to hold tension upon the belt. Most, if not absolutely all, spring tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more complex and expensive but don’t require adjustments and are less prone to user error.