Next time you utilize a drive belt, timing belt, or timing chain, you’ll likely have to loosen a tensioner pulley to remove it. Subsequent these general guidelines and specific instructions from your owners manual or repair manual, your belt or chain will function for the life of your car.
Toyota and other timing belt tensioners are loosened simply by removing them from the engine. You must slowly compress them in a bench vice and lock them with a pull-pin before reinstallation.
Hydraulic (not hydraulic-damped) tensioners are almost always located in the timing case, mostly on vehicles with timing chains, while some are used with timing belts. Hydraulic tensioners are powered by 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 entire year, make, and model information, 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 Car Pulley Belt spring maintains tension, while the hydraulic damper keeps it from bouncing under load changes. This prevents timing belts and timing chains slapping and jumping teeth and keeps drive belts from slipping and making noise. To loosen a drive belt spring tensioner pulley, refer first to the restoration manual or owners manual’s specific year, 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 essential.
To loosen an NAI tensioner, loosen the locking nut or bolt, then cool off the tensioner screw. Force the pulley toward the other pulleys or components, loosening the belt.
Spring tensioner pulleys, as the name implies, make use of 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 changes and are less prone to user error.