We got an S14 200sx into work running on 3...

took rocker cover off to find the oil was like tar, 2 camshaft spray bars were blocked, both cams fucked (worn badly) all rocker arms worn, one lobe was worn so bad the rocker arm had enough room to fall out and wedge itself in the head, hence it running on 3...

if you come across an engine like that, clean it as best as you can and run it on a good fully synthetic oil (its got some kinda cleaning detergent in it) and after a few K miles and maybe another oil change it should clean the engine up pretty well!