Could someone please tell me what hydraulic lifters are? What is the other type used?
Thanks for all the help!

 

Hydraulic Lifters are not Solid Lifters. The Tappet that rides on the Cam lobes can be solid, or a two part piece with a spring inside and a oil passage that allows the inside to be pumped up with oil. Solid lifters need to have the valve lash clearances adjusted periodically since as the cam lobe wears, and the rocker wears against the valve stem, the solid lifter and pushrod can start to clatter with the rocker. The oil filled hydraulic lifter runs quieter and "automatically adjusts" (to a point) because the clearance is dampened by the "squishy" (technical term) lifter between the cam and pushrod. There are oil passages that feed the lifters with oil pressure to pump them up. Bad oil pressure can show up as "ticky" lifters (with hydraulic lifters). Think of them as pushrod shock absorbers.