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So I posted the other day that my 2000 90 hp Johnson had a hole in the bottom end of the block. Tore the engine apart and the Starboard upper piston skirts are broken off. Also looks like it had detonation going on a little in just this one cylinder. All other cylinder and pistons look perfect and ran 118 to 121 PSI on compression test cold before I took it apart. This particular hole only ran 50 PSI. I need an idea where to look for what caused this so I can make sure it doesn't happen again. I checked the water pump and it has a new impellor so I dont believe heat was a factor. I just tore down all four carbs and base plates and they look new so I cleaned them an assembled and set to the side but found nothing obvious . If timing was to advanced wouldn't I see detonation in all holes? Now the bottom end of this motor has a large nipple with a hose that runs to a small square black box above the choke solenoid and I think its a vapor recovery system. Can this go bad and cause a lean condition? Maybe thermostat in that head?
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If timing was too far advanced whereas pre-ignition would take place... yes, that would affect "all" cylinders... or rather should!... However it seems that fate seems to always pick on one particular cylinder for some reason I cannot explain. A particular aspect of any engine to check before starting it up the first time as you surmise.
Besides advanced timing to a dangerous degree.... pre-ignition will also take place if a head gasket is starting to fail and is at a point whereas just a extremely slight spray of water is entering the cylinder. That extremely small bit, mixed with the combustion will have that aluminum piston starting to melt pretty quick.
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