Many vehicles today rely on hydraulic lifters in the their engines. Unlike solid lifters that have rigid designs and require frequent adjustment, hydraulic lifters work under a preloaded cushion of oil to open and close the intake and exhaust valves. Hydraulic lifters have inner plungers that ride inside a thick shell body. A small check ball and spring governs the intake of oil that enters the lifter casing. Hydraulic lifters rarely malfunction, but when they do, they can produce an annoying clacking or clicking sound. A few tests can reveal whether a hydraulic lifter has failed and needs servicing or replacement.
Assemble your hydraulic lifters in pairs per cylinder, according to how they came out of the engine block. You do not want to mix them up, or reinstall them in an order or location from which did not come.
Place each individual lifter in an egg carton hole, and use a felt pen to mark an "I" for intake, an "E" for exhaust. Mark the engine's cylinder number on the egg carton next to the corresponding hole. Sixteen hydraulic lifters will require two one-dozen egg containers, for example, or one carton for a V6 or 4-cylinder.
Take the carton to a work bench. Remove one hydraulic lifter and sit it face up on the bench. Use an old pushrod to shove down on the plunger top of the lifter as hard as you can. If the lifter plunger does not move or barely moves, place it back into the egg carton and mark it with an "Ok" symbol. Test each lifter in this fashion. Place an "X" next to the lifters that move noticeably with force or slide easily downward.
Take one of your "X"marked, or bad lifters from the egg carton. Place it face up on the bench. Use needle-nose pliers to remove the small circlip inside the lifter. Use a magnetic probe to pull the socket plunger out of the body, along with the large spring, small spring, check ball and retainer.
Place the parts in a separate can filled with kerosene and let them soak for 15 minutes. Clean all the parts with a toothbrush, then wipe them dry with a rag. Clean and dry each bad lifter separately in this fashion.
Inspect each lifter for obvious grooves and cracks. Discard the lifters that have obvious deformation. Use a file to round the threaded end of a 1 inch long by 5/16" bolt, and set the it aside. Lubricate each lifter with some regular motor oil inside and out with the tip of a rag.
Place the little spring in the check valve retainer. Set the check ball on the spring and attach it to the bottom part of the lifter plunger. Drop the large spring inside the lifter body. Fill the lifter body with oil until it overflows.
Drop the plunger assembly inside the lifter body. Oil will dribble out the small hole in the side near the top of the plunger. Stick a paper clip down inside the hole to seat the check ball. The plunger should slide down further. Push the plunger down with your fingers as far as you can.
Fill more oil into the lifter top. To compress the plunger down into the lifter, place your 1 inch by 5/16 bolt into the top of the lifter, with the filed, smooth side inside the lifter. Place a C-clamp around the bolt head and the bottom of the lifter. Turn the C-clamp handle to compress the plunger inside the lifter.
Insert a circlip into the lifter groove with needle-nose pliers and release it, so it locks inside. Remove the C-clamp. Perform this same function on the rest of the bad lifters. Make sure oil bleeds from the side hole inside the lifter body when you push the plunger in and probe the hole with a paper clip.
You can choose to disassemble all of your lifters, inspect and clean them. Reassemble them per the instructions, and bleed each one.