Big Bore Kits
 

I am trying to install a HighSpeed Performance Parts 58.5mm Big Bore kit on my GY6 engine. It was supposed to fit without any modification. But, I am having a problem getting the new jug to fit just right. It doesn't line up perfectly on the alignment rollers with either the case or the original valve head. The rollers fit in their holes on the new jug. But they won't let the new part match up to old ones.

The new piston fits OK. Anybody have experience with these kits? What should I do?