Poor Mans Pool Noodle Cylinder Hone.

[humanbeing]

Stock Yinxiang had that 65.5 config

Alternative way to tell which is which

[XLsior]

Good to know.
153mm push rods confirmed.
250cm3 cylinder with a 65.5mm piston.

I still advise measuring the piston when all you decide to do is purchase a new piston and rings and hone your existing cylinder.