2007 need motor guys input

[summitguy]

So my motor went down this week only had 750km on a rebuild short block Just looking for any help what could of caused this.
I have checked
carb boots
reeds
oil cable
rave valves .
ran fine all last year looks like it's been welded before

 

[slededjr]

What's the rest of the cylinder bore look like? That particular part of the cylinder is prone to cracking if overheated. Normal to see them welded. Maybe it re cracked and hooked the piston. If you could post pic of entire bore

 

[summitguy]

Here is another photo I have to pull the motor this week

 

[slededjr]

I can see it's cracked again. do you have temp gauge on this sled?
when did you purchase the motor? Still have warranty?

 

[Summitric]

Curious.. What kinda oil u running? How did plugs look?


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[summitguy]

This is the plug out bad cylinder .. From day one I've been using shell full synthetic