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Re: Hydraulic lifters (dsimic)

If you look at the bottom side, there's a metal button sticking out up inside there. It is like a piston and it is what touches the end of the valve. The top surface touches the lobe of the cam. A solid lifter looks the same on the outside, minus the holes. On a solid lifter, you have to carefully adjust the clearance between the lifter and cam lobe so that it will open the valve fully but not bind as the metal parts expand. The hydraulic lifter eliminates this by taking up all the slack it can, by expanding (oil pressure fills the lifter and pushes the button out) but also being able to give as the parts expand. Hydro lifters are noisy until they are filled up, because of the excess valve clearances. Once they are pumped up, the valve train is hydraulically damped by the lifters, kinda like shock absorbers, and becomes very quiet. As lifters wear out, they fail to pump up fully and allow excess clearance between the parts. The ticking sound is the cam lobe slapping against the lifter and the lifter bouncing up and down on the valve stem, exaggerated of course. A collapsed lifter is one that won't pump up at all and allows extreme clearance such that the valve doesn't open fully. It would make a much louder "clack" sound. In essence, worn lifters are like worn shock absorbers.
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