copper head gaskets

i know these are reusable but how many times can you actually reuse them?

 

Untill they look damaged ,..or
you can use them untill they show some signs
of torching or curling( green color) around the bores,
or untill they look warpy from the cylinder head moving around alot,
, or when ever you change heads,..and if o-ringed, sometimes the ring
impression on the gasket left by the o-ring from the heads and
block can get messed up,..
these are some of the things I look for.

 

I use them until they show signs of leakage at the O ring.