Hi xlt sport, I think you must have been totally obsessed with your Sulzer RTA engines, trying to sort out what the persisting problems are due to! Just a joke pal. Getting down to the problem, I would like to know whether all units' pistons are cracking, or is it only in one particular unit. Further if it is only in one particular unit & the problem persists with all piston crowns used, then we can infer that this is not a problem with the crown material, as you have already noted. Have you tried interchanging piston assembly of another unit into this particular unit? The problem should normaly cease off. If not & it still persists at the same area then it could be a serious one, may be, this is because of localised overheating due to coolant failure(the coolant supply to this particular unit might have been affected) in combination with problems of improper combustion such as afterburning & the fuel jet might have been directed onto areas close to the lifting bolts. The lifting holes which have stress raisers might have failed. Hence you should check onto the coolant supply to this paticular unit, whether there is any problem with the fuel valves & engine power balance. Normally engine performance checking should indicate whether there is any problem in the combustion process taking place inside this particular cylinder. Have you tried changing the cylinder head. This would eliminate any doubts regarding fuel jet dirtection onto the lifting hole areas. Even though these might be laborious they would surely yield results & eliminate the problems.
All the best
Paramagurubarn
