I have compiled this list as a start, please add to it and keep it going.
Keep in mind that this should be simple, quick and dirty, and using only tools hand carried into the yard.
In most yards all fluids have been removed along with batteries and catalytic converters along with the Y-pipe and O2 sensor.
Makes for determining a good engine more of a challenge than usual.
Obvious signs of a good engine can be low milage, clean and well maintained looking, other major obvious faults like a bad transmission, or most obviously severe body damage.
Look for the reason the car went to the yard, use your imagination and investigation skills.
Some clues to look for.
Coolant:***
If the coolant is clean and bright, it's an indication that the coolant system was good. If there is no antifreeze in the coolant and it is straight water, the engine was***likely overheated.
Water pump:***
Make sure it turns freely. Some engines could have a seized water pump which likely resulted in overheating.***
Thermostat:***
Put the thermostat in a cup of boiling water to see if it opens, if not, again the engine has likely overheated.***
Oil: ***
You can usually still find some left in the pan after removing the oil drain plug, or a little bit deposited on the dipstick. Make sure the oil appears to be normal and transparent without any milky deposits. Milky means coolant has mixed with the oil most likely from bad head-gasket.
A valve cover should also be removed. If things inside appear to be clean or have a slight brown tint, it's a healthy engine. If everything is black and there are thick oil deposits, this indicates the engine had a lot of blowby and oil was not changed on regular intervals, resulting in sludge buildup.******
Testing Compression: ***
Crank the engine a few times and check the pressure, on each cylinder.***If the key, battery and starter is intact this is a very easy task.***
However usually this is not the case.***
Cranking the engine by hand will not give accurate readings because the engine has to turn over fast enough to compensate for the leakage through the rings and valves.***
If a compression test gauge is unavailable, or the engine can't be turned over using the starter, the engine can be rotated by hand with a large ratchet to feel the resistance and pressure.***
It should sound like "ffoooK". If the engine turns too easy and no compression is heard, or not evenly spaced and only come from some cylinders, the engine is bad.
Please add to the list or correct any faults.