I have been (re)assimilated! Zongshen GS250

[SpudRider]

Here are the specs for the Yamaha, TW200 engine: 67.0mm Bore x 55.7mm Stroke

This information is incorrect; I made an error. :oops:
It appears Zongshen kept the TW200 engine bore, and increased the stroke to gain the extra 34cc engine displacement. Therefore, TW200 pistons, and piston rings should work in the 230cc, Zongshen engine. However, the connecting rod, cylinder, and cylinder head might be unique to this motorcycle. Also, the engine might be 5.5mm taller. A taller engine might require slight modification to the upper engine mounting plates if you wished to mount this engine in the 200GY-2, or Yamaha motorcycles.

This is the correct information; therefore, I have edited this post.
It appears the ZS250GS is basically a Yamaha XT200/TW200 engine, with a larger bore. It seems Zongshen enlarged the cylinder bore 5.5mm in diameter to gain the extra 34cc engine displacement. Therefore, Zongshen is using a larger piston, and larger piston rings than the Yamaha motorcycles employing this engine block. Also, Zongshen enlarged the cylinder head, and relocated the exhaust port on the right side, instead of the left side.

Spud