Had a truck roll in from an Independent shop the other day. It was a F150 with a 5.4L Triton engine. Apparently the techs changed the oil and upon restart, the truck no longer had any oil pressure. It ran fine, but sounded horrendous. Man, I wish a took a video of the truck before we tore it down. The sound it made would give you nightmares!
Pulled the oil filter off and it was dry - no oil whatsoever. I was ready to say it needed a black box, but my overly enthusiastic boss wanted me to tear it down more. Pulled the valve covers and noticed both guides were broke. Pulled the front timing cover off to see the chains flapping in the wind. Nothing but the cover was holding them in place. It's amazing it ran, and ran well aside from the noise. The chains were grinding into the front cover. I removed the oil pump expecting to find broken pump drive gears, but they weren't broke. Actually, it only appeared that the relief valve was stuck open.
The crazy thing was it appeared the thrust bearing was out as the crankshaft had been coming forward grinding against the oil pump. Nothing that I have seen myself before on this engine. Finally to put the final nail in the coffin, I pulled off a few cam caps and found some significant damage. Not only was there damage, but if you ran your hand in the "dirty" oil underneath the cap it was contaminated with aluminum from the cap itself. With this information I was able to ensure that this engine needed a major rebuild at the very least.
I mean yeah, could have saved a lot of time if we would have just sold the engine in the first place but the customer wanted to be sure it was without hope. Sometimes, that's just the approach you need to make.