What would cause a piston to look like this?

[renagade281]

Looks like flat spots or something... This was when I took the 44mm piston out today btw

[PIG]

Over heated and soft seized it.

[ThomasTPFL]

Foundry bees. They're like carpenter bees but much smaller. You can see the holes they bored in the ring groove, that black staining is their leavings.

[gsx600racer]

Id have to say heat(bluing on the wrist pin)and possible soft seize from the drag marks(on the 4 corners/sides) on the pistion.

From www.groupk.com/tec-seizures.htm

"Four corner seizure - This is by far the most common type of seizure found in personal watercraft engines. Both sides of the piston will show heavy scoring and seizure marks on each side of the wrist pin hole. The pattern of these four seizure points often appears to be a perfect square, hence the slang term "four corner". The scoring takes place in this pattern because those areas of the piston casting are the thickest. When the piston is seriously overheated, the thick areas will expand and distort the most. High output motorcycle engines usually experience this type of seizure pattern when a piston has been fitted with too little clearance. Most experienced , and well meaning, motorcycle mechanics would take one look and immediately say that insufficient piston clearance is the cause. However that diagnosis, on watercraft engines, would be wrong about 99% of the time.

Four corner seizures in watercraft engines are almost always a result of the engine creating more heat than the cooling system can exchange away. That is not to say that most cooling systems are under built, but rather that it's easy to make a modification that creates too much internal heat for even the most beefed up cooling systems. Even though a constant feed of cool water is being moved through the cooling system, the cooling system must be capable of exchanging the engine heat away at a rate quicker than the engine is creating it."