The 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. Subsequent these general suggestions and specific instructions from your owners manual or restoration manual, your belt or chain will function for the life 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 positioned in the timing case, mostly on automobiles with timing chains, though some are used in combination with timing belts. Hydraulic tensioners are driven 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 year, make, and model info, and you may have to use special tools for this type of tensioner pulley.
Typically, a hydraulic tensioner must be “reset” and locked after removing it from the engine. Take away the lock only after the tensioner, pulley, or slipper, and timing belt or timing chain are Car Pulley Belt 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 maintains drive belts from slipping and making sound. To loosen a drive belt springtime tensioner pulley, refer first to the repair manual or owners manual’s specific yr, make, and model information.
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 correct tool, release pressure on the belt. You will have 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 crucial.
To loosen an NAI tensioner, loosen the locking nut or bolt, after that cool off the tensioner screw. Push the pulley toward the other pulleys or 
add-ons, loosening the belt.
Spring tensioner pulleys, because the name implies, make use of a spring to hold tension upon the belt. Most, if not all, springtime tensioner pulleys are NAI tensioners and include a hydraulic damper. They are more complex and costly but don’t require changes and are less susceptible to user error.