I am still learning about diesels can someone give me a link explaining or a good explanation on how the valves work to impact compression and performance? I do not quite understand how the rocker arms, push rods, and valves all work together.

Thanks,

If the cylinder has good compression, and 400psi is good, the valves are sealing and the cylinder should run - if output less than optimal, could be the valves are not fully opening to spec, possible cause being a flattened lobe on the camshaft, giving just enuff lift to allow air to come in or exhaust gas to exit - at cranking rpm, this is enuff to give good compression readings, but would choke the cylinder at running rpm - also suspect on this engine are the nylon rocker-arm keepers which locate the rocker-arms on the rocker-arm shaft, keeping the rockers centered on the valves and pushrod\lifters - if the keepers deteriorate, the rocker-arm(s) will move sideways on the rocker shaft, losing some vertical movement, preventing full valve opening

Need to pull the valve cover to check that stuff out

Thanks for the replies. I put new nylon retainers when I did the heads. I should have kept better notes, but I do remember that the rocker arm had some wiggle on the shaft side to side, whereas the other rocker arms were tight and had no movement.

If I pull the valve cover can I turn the engine by hand using a breaker bar and watch the valves move up and down?

Is there anyway to know if the lobe on the camshaft is worn other than taking out the whole engine?

Thanks again for your help. I started this project knowing nothing and still have a ton to learn.

Good job, then - yes, you can use a breaker bar to crank it over, but if it were me wanting a quick first check, I'd disconnect the pink wire on the IP, use the starter motor to spin it over, comparing valve action on #6 to #4 and #2, also observing #8 for full travel - if they all appear similar, intake and exhaust, need to look elsewhere, but you should cross that bridge when you come to it, after this test.