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

Toyota and various other timing belt tensioners are loosened by simply removing them from the engine. You must gradually compress them in a bench vice and lock them with a pull-pin before reinstallation.
Hydraulic (not hydraulic-damped) tensioners are nearly always situated in the timing case, mostly upon vehicles with timing chains, though some are used in combination with timing belts. Hydraulic tensioners are powered by oil pressure from the engine oil pump and could press on a tensioner pulley (timing belts) or stress slipper (timing chain). You’ll likely need the entire year, make, and model details, and you may need to use special tools for this kind 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 teeth and retains drive belts from slipping and making sound. To loosen a drive belt springtime tensioner pulley, refer first to the restoration manual or owners manual’s specific calendar year, make, and model details.
You may need a special tool, but many spring tensioners have a square hole, for a 3/8” or 1/2” breaker bar, or a hex or square protrusion for a wrench or socket. Using the appropriate tool, release pressure on the belt. You’ll need to hold some spring tensioners while slipping on a new belt. Others may have a locking mechanism, like a hole for a locking pin or hex essential.

To loosen an NAI tensioner, loosen the locking nut or bolt, then back off the tensioner screw. Drive the pulley toward the additional pulleys or add-ons, loosening the belt.
Spring tensioner pulleys, because the name implies, make use of a springtime to hold tension on the belt. Most, if not all, springtime tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more technical and expensive but don’t require modifications and are less prone to user error.