Thought I had a blown headgasket but it seems no 3 cylinder bore decided to crack. Had a look at my info on the blocks I've had x-rayed for bore wall thickness but cant remember which blocks which. From my results A VG block can vary from as thin as 140 thou (3.5mm) up to 330 thou (8.3mm). Add boring and 20 years of potential rust and they can get pretty thin . Everything else from chambers ,pistons ,bearings etc are in excellent condition which is good to know at this power level . Cylinder 3 on one of my sheets is not too thick around the 160 thou before machining so with everything else being in good shape can only put it down to that if that's he block new block is at machine shop getting done must be all this cylinder pressure .