Well, with oil being all in the hull, Im believing it starved for oil on the back side. So if a wrist bearing or rod bearing came apart, would I have to replace the crank as well? I have been through the carbs several times as of late to get them right. And have done plug checks to make sure it wasnt too lean. Sometimes they actually looked rich. I really believe I have a leak in one of the oil lines. What does it sound like happened since there is hardly any carbon on the piston>?
This is the second one with photos recently that let go and showed little carbon on the top of piston crown. I see that and think well, WTF!? I'm wondering right now if the carbon was burned off. Normally there should be some carbon in the center and bare aluminum around the edges where the piston runs cooler and normally carbon does get washed by fuel, carbon all over the crown right to the edges is typically considered a sign the piston is running a bit on the hot side as the heat tends to cause the fuel to burn close to the surface and leave soot(carbon), my pistons have some carbon on the centers with bare aluminum port shadows around the edges, especially shadows from the ports. An overheated piston seems like will begin to melt first near the exhaust ports.
I'm trying to compare photos to get an idea of how to read the 951 piston crowns, but it's not easy to find such photos. So, I've been trying to compare to photos that do exist, such as these:
http://www.smellofdeath.com/lloydy/piston_diag_guide.htm
As far as trusting the crank goes after seeing the piston impact the plug electrodes, I'm hesitant.
Doesn't stop me from trying though, do you know which jets are in the carbs, are they #70 pilots and #162.5 mains? My experience is the #70's seemed a bit too lean in mine but my gripe was over a flat mid throttle response. Fatting up on the pilots also makes the top a hair fatter as well.
Anything that might make the top end leaner such as running a higher flow airbox or less restrictive filters could get a few more RPM at the potential expense of roasting a piston, simply b/c less restriction would equate to a bit leaner ratio. The leaner you go with a 2 stroke, it tends to make more power to a point, till it hits that magic 14:1 ratio and it's gonna be real close to detonation, which when it does, if detonation does happen, and it will if it's lean enough or the fuel is crappy enough (Can you say Seafoam, LOL!), then 2 strokes are known for quickly roasting pistons, I've seen plenty of big ol' holes burned in 2 stroke Merc EFI outboard pistons, and Johnson 100psi v6 carb motors too, not just Rotax motors. It's common to see broken rods and shrapnel all over inside when they go pop, it gets ugly, the powerheads get yanked and off to the reman shop they go!
Could be you lost lube as well, I'm not trying to rule that out, I wanna keep an open mind, not an open/shut case. I guess lack of lube would show scoring on the skirts.
