Ran the engine for a short time and it sounded like I had a loose lifter. Then the sound changed and I turned off the engine. this is what I found -again- on the #4 exhaust. The rocker to the left is also not centred properly.
#1 exhaust is also moving off centre!
The rocker on the left is from the crate engine and on the right is the one from #4 cylinder. It seems that GM became aware of the issue and modified the rockers to stay centred.
The push rod from #4 is slightly bent compared to one of the original units. I’ll use the old push rod as a replacement.
I’m now swapping out all the original rockers with the units off the crate engine – the crate engine had very little wear before it spun its bearings. I’m using a pad to tick off each cylinder as I give the lifters one turn down from zero lash. I’m following the service manual and adjusting half the valves at TDC and the other half after a full turn of the crankshaft.
This is the right bank with the engine running. All the rockers are staying centred on the valve heads. When the engine was warmed up some I reset the valves. Oddly enough I had to loosen the valves over 1-1/2 turns to get the valve to rattle. With zero lash I turned them down 1 full turn. Internet references often say that cold adjustment is fine, but I also found references saying that one full turn hot or cold is correct. I prefer to set them with the engine warmed up. Not so messy If you cut the top off an old valve cover and use clips for something similar to stop the oil squirting from the top of the rockers. I add an old towel over the exhaust manifold just in case.
Next: time for a test drive.