Leak Down Test

when performing a leak down test how will you be able to tell if you have a cracked head or blown head gasket?

You should hear/feel the air coming out of the adjacent cylinder's spark plug hole.

It all depends on how it's blown, and/or cracked. Often, you will get the cooling system start to pressurize (the rad hose gets firm, or if the rad cap is off, bubbles come out. )

Sometimes a blown HG will leak to an adjacent cylinder or to the crankcase. Sometimes a head that's cracked around a valve seat will push air past an intake or exhaust valve (although this is more indicitive os a burned/leaking valve).

So, generally, you can confirm a blown HG or cracked head in this manner. But an absence of such symptoms does not exclude the possibility of a problem.

A good 100psi on each cylinder under test should be good!
see www.youtube.com/watch?v=jG_RWs8ckp4 (http://www.youtube.com/watch?v=jG_RWs8ckp4)