Picked up a cheap omc v4.. why did she blow up?

[flabum1017]

The timing advance will not go past the timing stop....... unless the timing stop came loose, there was no problem with the timing per-say.

[flabum1017]

Both Locator pins are present in each piston. I did notice the timing advance couple between the throttle and trigger base and completepy broken. Would that cause it?Attachment 368027

Attachment 368028

Attachment 368029

The piston on the right looks like the locator pin is missing and came out.......... was that the top piston?

[JoshKeller]

Heres a better picture after cleaning the junk out of the ring grooves. I wonder if they stuck open thermostat caused the ring to carbon up and break on the port? Seems like a long shot BOTH pistons would go in the same exact place though. The pins are not as high as the bottom rings, but they are definitely there.

[flabum1017]

Nah, something came loose and went through that side. I have seen reed or carb butterfly screws do that or possibly something loose under the hood got sucked into the engine. Carbed rings won't do that. how do the reed valves look?

[H2OPERF]

Any marikings on the inside of the pistons as to who they are made by, doesnt look like wiseco by the .030 marks, one pic shows ring wear pattern riding only on outer edge of land/ funky wear pattern on lower edge of pistons , possibly from cheap pistons / improper bore job like racer said, maybe not cut at the bottom properly (funky wear pattern ) , port not chamfered properly as rings wore and maybe with a little help from carbon jacking got more knife edged caught and tore up. Delectors are not melted. Dave

[H2OPERF]

Or as was said above could have had something go thru it, usually one of the ports will have the fist sign of the initial screw or what ever got caught mark on it. I know most don't do much chamfering on cross flow ports but i had a 140 v4 back in the 80s with high ringers, got pistons for free no body wanted them, all ports were radiused by hand and it ran for ever never had a ring fail. dave

[FMP]

Maybe the end gap wasn't checked and it bound up. Who knows what the builder did, can you get .040 rings for these pistons? Maybe he .010 upped these two rings and didn't fit them correctly?

[racer]

Looking at those photos looks like pin is sunk enough to allow ring to pass over. If the ring was broken most likely the issue. Not from timing as no sign of detonation

[FMP]

I see no pins, just holes?

[flabum1017]

I see no pins, just holes?

You can even see where the pin came out and caught the port......or is that the pin pushed in and the scratched from a ring that caught?...

[FMP]

I see no pins, just holes