citroen berlingo van 1.9d 800 1997?

engine is turning over quickly - have checked cambelt - timing ok - very little compression. the guy has run the van dry (very little water). have taken head off, head gasket fine, checked pistons - little bit of play in each one - tipped diesel onto each bore and the diesel hasn't seeped through. I there supposed to be a little bit of play in each piston. Failing this is it possible that the head could have been warped due to losing water. the guy who previously owned the vehicle informs me he stopped and van cut out and a puff of smoke came from under the bonnet. help please i am completely baffled.