Next time you work with a drive belt, timing belt, or timing chain, you’ll likely need to loosen a tensioner pulley to remove it. Subsequent these general guidelines and specific guidelines from your owners manual or repair manual, your belt or chain will function for the life of your car.
Toyota and additional timing belt tensioners are loosened simply by 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 almost always situated in the timing case, Car Pulley Belt mostly on automobiles with timing chains, though some are used in combination with timing belts. Hydraulic tensioners are run by essential oil pressure from the engine essential oil pump and could press on a tensioner pulley (timing belts) or stress slipper (timing chain). You’ll likely need the year, make, and model info, and you may need to use special equipment for this kind of tensioner pulley.
Typically, a hydraulic tensioner needs to be “reset” and locked after removing it from the engine. Take away the lock only following 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 tooth and will keep drive belts from slipping and producing sound. To loosen a drive belt springtime tensioner pulley, refer first to the repair manual or owners manual’s specific season, make, and model info.
You might 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 tension on the belt. You will have to hold some springtime tensioners while slipping on a new belt. Others may possess a locking mechanism, like a hole for a locking pin or hex key.
To loosen an NAI tensioner, loosen the locking nut or bolt, then cool off the tensioner screw. Force the pulley toward the additional pulleys or add-ons, loosening the belt.
Spring tensioner pulleys, since the name implies, use a springtime to hold tension on the belt. Most, if not 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.