Hello all, been gone for awhile, because the Cummins had been running smoothly, just recently it has developed a change in idle rhythm and tone.

So pulled the rocker covers for a lash check and adjust and found the intake valve tips recessed into the retainer on cylinders 3and 4. Pulled the retainers off to check the lock groove on the valve and found the retainers are cracked. Engine has 285 thousand on it but doesn't use oil, valves move freely in the guides.

What would cause this? Lash was not too far off specs on other cylinders. Can't get pics to upload.

 

The valve seat sagged. Looks like that.

 

To me this sounds like a good catch for the wrong reasons.
The cracked retainers need to be fixed, but they would not change the sound of the engine. (Except when they let go completely, then it would sound like a cement mixer loaded with marbles crashing into a dynamite plant)

I have never seen a cracked retainer on a Cummins, so I can't help you there, but valve seats sagging would also be a first for me on these engines..

 

One retainer was hitting the rocker arm which I think is what was causing the idle change. Low spring pressure and changed timing on that valve. I installed all new retainers (side rant) Why are Cummins parts made in China? And all valve tips are correct in height, so I'm fairly sure no sagged seats. It does have 285k miles on it now.