Just got myself a new blaster and was tearing it down. They tried saying it was a big bore but from what I know I didn't think it looked like one. Help please. No Yamaha marking and no signs of any grinding at all.
It doesn't look like any aftermarket 240 going by the look of the casting and no Boyeseen ports. It could be a sleeved 240? Probably a Chinese e bay "ish" cylinder. Do you still have the piston that was in it?
It looks like those crappy eBay cylinder kits since it doesn't have any markings, doesn't look like there is any champhering, and it looks like the sleeve liner is flaking away just like when Ken tried to bore one of those eBay kits
And it looks like it had a bad seizure too
I would buy an oem cylinder and send it to a builder to bore with a new piston