There are only a few reasons why a cylinder would have 0 PSI with a compression check: 1) the intake valve doesn't open, 2) the piston doesn't move in the compression stoke, 3) a complete blockage of the intake passage in the head; 4) the check valve in your compression gauge didn't open during check of that particular cylinder. Do you mean really mean no measurable compression pressure, or just very low, such as to be taken as "zero"? Crowns occasionally break off pistons at one of the ring grooves, as mentioned, and will result in zero compression pressure, but they make a lot of noise (a huge amount) and cause a 'misfire' you would notice with the engine running. If the push rods and rocker arms are all functioning as you say, or even if not functioning fully, there will be valve action and air entering the cylinder, therefore some level of compression pressure. I can't picture a complete blockage of the intake port for that cylinder. Was that cylinder actually 'dead', as in not producing power? Given all you have said about appearances of everything you have taken apart, I suspect your compression gauge malfunctioned- I may be wrong with that, but if not, you may be going to needless expense to correct something that doesn't exist. There is an inconsistancy with your findings that needs to be resolved.
Before you take the oil pan off, turn the engine to see if all the pistons move as they should. If #6 piston doesn't move as it should, ok, take the oil pan off.
Harvester
