Bit of a thread rivial: How do I know if the lifter is bad and cannot be cleaned and returned to service? They are so simple I gather it comes down to clearances between the "piston" and the lifter body. Am I right assuming this. What should they be when measured with vernier calipers? I've got them all out and have cleaned them and trying to bleed them in a tub of oil but they are not getting harder to push down.