I am replacing the head gasket on my 93 D250. In the process I've discovered something that confuses me. When I backed off the valve lash adjusters, all rocker arms became free from their respective valves, except for a single rocker in cylinder 4 (I don't recall if it is an exhaust or intake valve). It doesn't seem right that if I fully back out the adjustment screw, the rocker and valve don't disengage. What is the best way to remedy this? Shim under the rocker pedestal? Grind material off the rocker or valve? FWIW I bought the truck about twenty years ago at 100 thousand miles from an older couple and I don't believe they had any engine work done to it. Today I put the new head gasket on, reinstalled the pedestals and pushrods, and torqued the head bolts to 70 ft lbs. Plan to torque to final 125 tomorrow. When I reinstalled the pedestals the same problem with cyl 4 was there. Prior to commencing head gasket repair the truck ran OK for a 350 thousand mile truck, so I believe the valve almost closes, or does close but there's no valve lash. Yes, I should have studied further prior to commencing reassembly, but didn't. TIA for any advice.

 

Unfortunately the only proper repair for this problem, is to pull it apart and inspect that valve/seat area carefully. It could be a badly worn valve, or a seat area that is pounded out. Putting it together and running it could work for a long time, or until the end of its time. In this case, better safe than sorry.
I’m currently dealing with a loader engine that had what turned out to be the same kind of problem. It destroyed the engine completely when the valve head finally broke off and the cylinder beat itself to death under full load. Ended up with cracks in the cylinder wall and head in the process.

 

I agree with what pind said. First, are you absolutely positive that you checked the lash with the cam on the low side? No lash after backing off the adjustment is a sure indication of something failing, such as a valve or a valve seat or that you are checking on the wrong stroke. If either of these fail, then expect to shell out major bucks for an expensive and unnecessary engine repair. Sure, a work around by grinding off material will work for a while, but you are only delaying the inevitable expensive engine repair after something breaks and severely messes up other parts.
Let us know what you discovered to be the root cause of the problem.

 

Thanks for the input, despite it sounding grim. Mexstan, the answer to your question "are you absolutely positive that you checked the lash with the cam on the low side? ", is NO, I'm not sure. Prior to removing the head I removed the injection pump for a reseal (head at rear of IP had leak). Prior to removing IP I rotated engine till keyway in pump gear was facing up (about 12:00 o'clock). I locked the pump in that position and haven't moved the engine since, to retain previous engine/pump timing. (I haven't started IP repair yet.) So, I have no idea where cylinder 4 valves are in relation to cam. I started this thread because I assumed, hopefully incorrectly, that if the valve adjusters were fully backed off, there would be lash (rocker loose). Is it possible that the cylinder 4 valve could simply be high on a cam lobe and what I observed is normal? I hope so. I don't want to revolve the engine to find out until the injection pump is reinstalled.

 

If you did not rotate the engine while checking the lash, then there is a very high probability the cam was on the high side on at least a couple of valves.

 

Thanks again. So there is more cam lift than can be compensated for/offset with valve adjusters. I did not know that. It is music to my ears, however!!!!!!!!!!

 

Here is one way to adjust the valves:

Rotate the engine until the TDC mark on the damper is at 12 o'clock.

If both #1 valves are loose then #1 is between compression and power stroke, so adjust intake on 1, 2 and 4 and exhaust on 1,3 and 5. Feeler gauge goes between the rocker arm ad the crosshead.

If both valves on #1 are NOT loose, it's in overlap between exhaust stroke and intake, so you adjust intake on 3, 5 and 6 and exhaust on 2,4 and 6.

Then rotate the engine 360 degrees and do whatever group you didn't do.

 

Thanks again Mexstan! All my valves are loose except the one in cylinder 4. After I reseal/reinstall IP I plan to rotate engine till #1 is at TDC, as determined by the timing pin below IP, then adjust valves as you recommend.