Found a set of heads locally on CL. He claims they came off a running engine. Any advice on what to ask, or obvious or hidden gotchas? Or is it pretty unavoidable that you're taking a roll of the dice?

Rolling the dice with out disassembly. Look for cracks around the spark plug hole and check around valve seat for loose material. Use steel ruler to check deck for straightness. Check valve stems for wear.

Don't buy heads that are dirty and carboned up ,ask me how I know,tends to hide hidden cracks in several area's as mentioned.
You need to factor in machine work if the heads are used,heads on the T4 are a weak point and need to be up to scratch before going on .

I figured used heads are going to be at least a little dirty. Here's what they look like- it looks typical to me, but I've not looked at a ton of used ones...

Click to view attachment

If I got them, they would be for a daily driver, nothing fancy.

New heads are being sold for reasonable prices. Do not spend too much on used.

Hopefully Len or someone with more knowledge can chime in, but...

Look for cracks across the spark plug holes inside the chambers.
Look for cracks around the short radius inside the port.
Look for any signs that the intake seats are moving or are thinking about dropping out.
Look for valves recessing, or stretching, or deforming in any way.
Look for exhaust valves that have been overheated and may be starting to burn.
Look for mushrooming or divots in the valve tips.
Look for valve guides that are loose.
Look for exhaust stud bosses that are in good shape, not stripped, and have no cracks.
Look for rocker studs that are pulling out.

Remember that the 2.0 heads are known for cracking, and sometimes they drop seats. And dirt or carbon can hide cracks and other damage.

I'd personally favor the new heads, but I am now in a position where I can more easily throw money at the problem than time, or than run the risk of a failure shortly.

--DD

How many exhaust studs are missing?

UPDATE: I went ahead and got them. The guy wanted a c-note and a buddy said I'd get a great deal on heads, or a hundred bucks worth of industrial art. So I got 'em.

They need some clean-up before I can really check most of the things listed above, but exhaust studs are all there, rockers look OK, valves look OK, no major problems I can see so far. If I find any major hidden issues, I'll post a "show me your pencil holder made from old cyl heads".

Thanks for the input, all!

I was speaking with that guy as well, but he didnt know what size they were. Potentially 1.8L?

They're 021 101 371S which makes them 1.8s, and the 41mm valve which should be a '74. It's dirty but looks OK - not really going to know until I get them cleaned up some. I'll go through Dave's check list above.