Originally Posted by 1967brutus

I cannot come with numbers, because I do not have torque spanners that small, but you know when you unlock your frontdoor from the outside, using the key only? Not the part where you pull back the tongue, but that last little twist where you have to pull back the latch against the spring using the key?

Not much tighter than that.
Another not very accurate description: You know those L-shaped allen keys, the M3 size being about 2,5" or so in lenght? A thumb on the bend, and the tip of the indexfinger at the long end, and no more force than what still is "comfortable".

In the end, tightness is indeed not the main thing, there is a fairly broad range where the head will be sealing properly without damaging the threads. Tightening evenly is more important. It is all a matter of "feel", don't overdo it.

Since you're asking about torque, I assume that you have had some leaks or whatever, leading to the question? Tightening a head is simple: To square the head down, press down on the head in the middle (where the plug is) with one hand. Snug up the bolts in a cross wise pattern by rolling the allen key between thumb and fingertips of the other hand (use the long end in the hex head). Now this is important: When you have snugged up two opposed bolts, check whether tightening the 2nd bolt did not tension up the 1st one. Check by trying to loosen it, should take the same force as when you snugged it up. If that is the case, the head lies on square. If it isn't, there is probably some dirt on the landing face between liner and head.
After snugging up all bolts this way, making sure the head is squared, then tighten, and each bolt should take fairly accurate the same force to turn the same amount of degrees.
For .40~.60 size engines, after properly snugging up, the tightening angle should normally be something like 60 degrees, maybe 90 tops. That is another way of getting bolts equally tightened without overdoing it.