Hydraulic valve lifters use oil pressure and a spring to keep the intake and exhaust valve opening and closing properly. The interior of the lifter body has a small pump shaft, oil hole and spring that actuates when the rocker arm comes in contact with it. Worn lifters or lifters that have accumulated air into their interiors, can not hold the proper opening and closing pressure. Vehicles that have excessive tappet noise can be the result of air in the lifter body. Purging the air from hydraulic lifters requires the removal of the lifters from the engine block, and the use of a few tools and chemical cleaners.
Make sure you have removed all of the hydraulic lifters from the engine. Place the lifters in an old egg carton and label them, referencing from what location they were removed. For instance, label them, cylinder 1-intake, cylinder 1-exhaust, cylinder 2-intake and so on, using abbreviations. Take the lifters to a work bench that has vice.
Sit the lifter -- top facing up -- on a work bench. Place a push rod down into the lifter seat and shove down hard. If the lifter has no plunger action, even a fraction, it does not need a bleed. Test all of the lifters in this fashion. Extract only the lifters that compress or feel "spongy," with excessive play. Wipe down the outside of the lifter body with kerosene and a tooth brush. Wipe the lifter dry with a rag.
Use circlip pliers to remove the top C-ring in the lifter top. Compress the C-ring and pop it out of the lifter face. Pull out the small push rod socket, to reveal a small oil meter disk attached to the plunger. Pull upward on the oil meter disk to remove the plunger and spring. Remember how the components fit together.
Place the parts in a can of kerosene and clean them with a tooth brush, including the inside of the lifter valve body. Wipe all the parts dry with a rag and lightly coat them with oil. Set the lifter valve body on the bench with the open face pointing upward. Pour motor into the opening until it overflows. Attach the spring to the bottom of the plunger and drop it down inside the lifter valve body.
Clamp the lifter in a vice with the topside facing upward. Place the push rod socket into the opening of the lifter valve body and push it up and down with an old push rod until oil seeps out of the lifter valve body hole. Hold pushing pressure on the push rod socket, while you install the C-ring back into the mounting groove with the circlip pliers. Pump it a few more times until it tightens up and no free-play can be felt.
Repeat the disassembly, cleaning and bleeding procedure with each suspect hydraulic lifter. Be sure to install them back into the engine in their respective locations, according to your reference marks.
Change the engine oil immediately after performing the bleeding procedure. Let the engine run for at least 30 minutes. Clean out the lifter seats with carburettor cleaner and compressed air.