engine gone?

i have 2004 ion quadcoupe manual has 238000 miles never an oil leak car has been maintained well.came back from dreive shut it off came back hours later to drive it sounded rough like a knock shut it down tried to start again and it made a little backfire havent touched it since did pull valve cover chains not broke but noticed i can pull the rocker rollers off without tools they just sit on top dont no if its supposed to be like that ,they are loose on cam closest to front of car not the back one any help would be appreciated been reading this forum for years you guys have helped me so many issues thanks for being here sincerely