In the smaller inner sleeve there is a metal cap in one end that contains a small metal ball. You can pop the end of the sleeve off with a screwdriver.
I have seen them MISSING the steel balls, hence no oil pressure in the lifter body and no hydraulic lash adjustment capability.
To test new lifters, stand them up in a tray of clean oil and push down on the top cap where the pushrod sits. The lifter should fill with oil but then push back against the pushrod as it "pumps up" ....
lifter float (the lifters over pumping up) back in the day lost many races!
Back in the day I would make hydraulics into solids by machining solid body inserts for the main bodies.
