From what a specialist told me it really comes down to the condition of the block thus the question is "How long is a piece of string?". He was saying that he is seeing many blocks that are now becoming brittle due to age and also down to how thin the walls are on a 1.6 CVH. The 1.9 is not meant to be as bad in this respect and neither is the Zetec bottom end.

I am running 225BHP on a ZVH and it has given me enough grief, albeit over silly things. I have done around 5-6k in it this year mind you, probably 3 times the amount it has done since the car was finally rebuild around 4 years ago and the engine 2 year ago (I'd have preferred the 1.9 long block to have stayed with the car but hey ho...).