Next time you utilize a drive belt, timing belt, or timing chain, you’ll likely have to loosen a tensioner pulley to eliminate it. Subsequent these general suggestions and specific instructions from your owners manual or repair manual, your belt or chain will function for the life span of your car.
Toyota and various other timing belt tensioners are loosened simply by 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 with timing belts. Hydraulic tensioners are run by essential oil pressure from the engine essential oil pump and may press on a tensioner pulley (timing belts) or pressure slipper (timing chain). You will likely need the entire year, make, and model info, and you may have to use special equipment for this sort 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, while 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 noise. To loosen a drive belt spring tensioner pulley, refer 1st to the restoration manual or owners manual’s specific season, make, and model information.
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 correct 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, such as 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. Press the pulley toward the other pulleys or components, loosening the belt.
Spring tensioner pulleys, as the name implies, use a spring to hold tension on the belt. Most, if not absolutely all, springtime tensioner pulleys are NAI tensioners you need to include a hydraulic damper. They are more complex and costly but don’t require changes and are less prone to user error.