That’s a retaining wire clip from a hydraulic lifter. Check all of them before you put it back together. You can replace them (because they’re junk) with internal snap rings and this won’t happen again. Also make sure the pushrod is seated in the cup of the lifter before adjusting them.
I've heard nothing but problems with hydraulic lifters, is there a quality lifter anymore? American use to be known for their quality and people took pride in their work, what happened?
