[Vwdiesel] cracks between valves

[Pam & Doug Boes]

How big is too big? I took the head to the machine shop and the machinist
said the rule of thumb is that if you can get your finger nail into the
crack(s), they are too big and it is time for a different head. I have one
crack at each set of valves and all are just big enough to hook my finger
nail :-( Can the cracks be peened shut and prevent further growth?