Lets review this situation:
No compression in one cylinder, next cylinder has normal compression, zero again on the offending cylinder: gauge seems to be working.
Head is off, all valves appear to be 'normal', no broken or badly burned valves; therefore, valves are not the cause of 0 PSI.
Had visible valve action before removing the head: no inoperative valves, therefore air is getting into the cylinder, and being more or less contained by the valves, so some compression pressure would be measureable.
If the timing gear broke during operation, the engine would have stopped where it was, and there would have been noise during the last few revolutions. Compression could be zero or very low in some cylinders, depending on valve position, if the camshaft didn't turn during the compression check, but 5 cylinders have reasonably normal compression. Conclusion: timing gear is not broken and camshaft is turning.
Engine seemed to lack power the last time the vehicle was driven, no reported noise during the last operation. Is that a fair statement?
So: air in reasonable quantity is getting into all the cylinders; examination indicates no broken valves, the head gasket is in reasonable condition, and there are no holes in pistons. At this point, a broken piston with the crown separated from the skirt, above the wrist pin seems the most likely possibility. Turn the engine, fuel line plugged, and see if all the pistons move as expected; if one doen't go up and down as it should, there lies the trouble.
Keep in touch.
Harvester
