you might have to replace the lifters.
Seafoam Motor Treatment.
Sometimes putting a jug of transmission fluid in your oil will clean the junk out of your lifters and stop your noise - if it is an older vehicle with adjustable rockers you can adjust and get rid of the knock.
To bleed the hydraulic lifters on a 2003 Opel Corsa 1.4, first, remove the valve cover to access the lifters. Submerge the lifters in engine oil and manually compress them to expel air, repeating this until no bubbles are visible. Reinstall the lifters, then reassemble the valve cover. Finally, start the engine and let it idle to ensure proper operation, checking for any unusual noises.
"Could you please stop making cat noises?"
have your valves adjusted adjust your valves
Hydraulic lifters are nonadjustable. Chances are the noise is coming from play in rocker arm, or ignition out of time. If you are sure it is the lifter, then it must be replaced.
eat something
The lifters are in the cylinder heads.The lifters are in the cylinder heads.
If they are mechanical lifters, then there is an adjustment under the valve cover. If they are hydraulic then there is no adjustment, and while a different weight motor oil or special additive may help the ticking there is not real way to stop it.
they have no lifters
the lifters are on the overhead of the engine the lifters are on the overhead of the engine the lifters are on the overhead of the engine