The Isuzu 3.2/3.5 liter engines have mechanical lifters. They are adjusted by replacing solid disc shims that are captive by the guide that goes into a polished port in the head that the valve springs valves fit in. I doubt very seriously that a shim or guide has come off or apart since they are both pretty substantial pieces of solid machined steel.


As a side note, I have found the easiest way to adjust the valves is to take measurements of the lash gap and pull the cams to replace shims, IF NEEDED. Once you have pulled the cams from the head and can identify the alignment marks, it is no big deal. Since they are gear driven and not directly connected to the timing belt, it takes about 15 minutes to pull both cams on one side and put them back on. Takes ten times longer to pry all the lifter shims from the valve stem cups, than to pull and replace the two cams.