I've been always thought that, when a cilinder compression falls below 60/80, I should summarily replace it.
However, yesterday, as usual, I was surprised when I read the Mike Busch's article about compression checks. He says that the minimum acceptable compression, according to TCM, should be around 50/80, as long as the pressure loss is not thru the valves.
The article:
http://jtatwins.com/Compression/putt...n_context_.htm
What limit do you use to cilinder compression?