Hyundai Sonata,1997, has oil coming out of tail pipe

[Ferngee]

1997 Hyundai... Sonata..4cyl.. with 87,000 miles.. has low compression.. So..I took the valve cover off and notice that several lifter were sitting on the side of the piston..Would that cause low compression? 4 lifters were off...Can I just pop these back on or do I have to get new lifters.. It looks as if I can just pop them back on.. What would cause them to pop off?** I am still looking for the little valves that you were talking about... are they under the rocker arms?* or could these lifters be the cause of the low compression...* what are your thoughts??