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Old 06-23-2013, 02:43 PM
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Default RE: OS 1.20 Go Boom....!!!

ORIGINAL: proptop

IMO the piston lost parts of it's skirt...which locked it up....connecting rod didn't like that and couldn't decide which way it wanted to go...developed a split personality...

Seen another O.S. 1.20 with the bottom of the piston skirt missing...tore the innards up good, but not as extensively (throughly ) as yours![X(]

It makes me wonder sometimes, when I look at how much material they (O.S. ) have removed to lighten the piston....there isn't a whole lot left down there and it must flex somewhat because of piston rocking / side loads...
I agree with your theory, however, none of the piston skirt parts are damaged. They are all clean breaks, no gouging or smashing that would be consistent with trying to lock anything else up.
I think, and who really knows, that the cleanly broken big end piece (2nd from left, top of pic next to the big bushing) actually fractured first, thr crank with it's interia and prop rotating came around hit the opposite side of the rod (You can see a good sized dimple in the left side of the rod beam just down from the big end) snapping the top and spitting the prop off.

From what I heard and saw when it happened, I am willing to bet that was the sequence. The engine stopped "NOW". When the crack sound was heard, the engine was already stopped dead and the prop was on it's way forward and off the right of the airplane. If I had to bet, that engine didn't make 1 or 2 revolutions once the rod fractured. And I'd say it was nothing more than fatigue from what I can see under a magnfying glass looking at the material. It's not a sheared or torn. It's like someone simply lifted off that piece. It fits back on that big end perfectly, placed together you cannot tell it's broken.

Just my post rod kicking guess...