1999 Dodge ram 1500, 5.2 liter. 117000 miles.
I work on vehicles to pay for my dirt bike racing, (mechanic for 25 years)
This truck came to me with a skip on # 2 cylinder. Found a failed roller lifter that chewed into the cam lobe.
I replaced the cam, lifters, timing chain set, and gaskets. It started right up. I let it run, as I topped off the coolant. Changed the oil and filter, and road tested it. All seemed good. The next day I rechecked the coolant, and oil, and started it to let it run. It stalled on it's own. I restarted it and it ran again for a couple minutes and stalled. This time when I went to start it, it "clunked". Now it won't budge. I remove the plugs (thought it hydro locked) valve covers, and loosened all rockers. You can turn the crank 7/8 of a turn, and it will stop, and then the same backwards. Any realistic ideas?????

 

Foreign object in the cylinder.

Perhaps whatever caused the roller on #2 to grenade (burr, crack, misalignment in the lifter bore) happened again and this time took the valve with it. You can remove the valve cover on the passenger side and collect the upper valve train on #2, remove the pushrod and peek down to the lifters and see if they are still intact. Thats about all you can do before tearing the engine apart again.

7/8ths a turn definitely sounds like one cylinder on the overlap has piston to valve clearance issues, and since it's not happening anywhere else, my guess would be one valve is bent enough that during the compression stroke, it's closed enough to get the piston by, but during the overlap, it hits.

My guess would be that the one cylinder in question would have zero compression even on the compression stroke.

if you have an air compressor with a spark plug sized/threaded air nozzle, you can find the offending cylinder by pressurizing each cylinder and finding the one that won't hold any pressure through the range of crank movement you currently have.

 

The original issue was cylinder #2
Cylinders # 4 and # 7 are approaching top when it locks.
I will look into the lifters, to see if I can pull them upward with a magnet (If one is locked into a bore)
and see what gives when I put air into the cylinders, as I do have an air hose for this

 

Wonder if it dropped a valve.......

 

Put air into the right bank cylinders. #4 has air out of the intake. Valve measures a slight lower. Are these prone to munch valves???

 

Not typically, unless it's been pushed excessively hard. The stock springs are weak, and valves will float at higher rpms, but for normal use they are adequate. They are pretty worthless at any lift over .480

The stock valves are steel, not even stainless, so they bend easily. Is it possible you got off when degreeing the cam? What timing set did you use?
I've also heard of valve springs breaking right near the seat, so it's not readily visible but compromises the operation of the valve.

 

Did you happen to put a beefier aftermarket cam in?

The 5.2L has flat topped pistons and far less piston to valve clearance than a 5.9L with dished pistons.

Aftermarket performance cams always need to be checked for clearance in a 5.2L.

 

And are two piece as well...

 

I did have a lot of trouble finding a "stock" cam. Sealed power was back ordered for over three weeks. A local machine shop got me a clevite unit, and I was clean on wanting a stock unit, and didn't want to get into springs and /or computer changes. I replaced it like it was stock, and marked the distributor clearly at TDC before removal. The funny part is that it ran (and I drove it a few miles) fine. The next day I removed the battery cable due to replacing the rear ABS sensor. I started fine and ran for about 5 minutes and stalled. I restarted it, and again it ran and stalled. This time when I tried to start it, it turned and "cluncked." Thus discovered that the engine crank wouldn't rotate a full 360 degrees.

 

I will check the cam specs, and I was sure the timing marks were spot on.