http://www.yingangmotor.com/
YG250NF
25hp@9000 rpm
16lb ft of torque @8000 rpm
top speed 87mph
30.7 inch seat height.
weight 322 lbs
EngineModel YG170MM
EngineType 1-Cylinder, 4-Stroke, water-cooled
Displacement(ml) 250
MaxPower(kw/r/min) 19/9000
MaxTorque(N·m/r/min) 22/8000±500
Idling Speed(r/min) 1500
Consumption(g/(kW·h)) ≤354
Cylinder Diameter * Stroke(mm) 70×65
Operating cubage of the cylinder(ml) 250.2
Compression Ratio 11:1
Ignition CDI
Spark Plug Model TORCHC9EH
Carburetor Model PZ30V
Lubricating Capacity(L) 1.6
Petrol Type 90#
Clutch Manualã€Coil Clutch
Starter Electric
Lubrication Pressure Splashing
Transmission 6 speed
NetWeight(kg) 39
Packing Size(L×b×h) 460×395×575
Notice that the engine is stamped with Shineray on it, I would say that the engines used on the Shineray motorcycles are manufactured by Yingang.
The water cooled DOHC 4-valve is a copy of a Honda NX250 engine.
http://en.wikipedia.org/wiki/Honda_NX250
That engine 170MM can be found on several Chinese motorcycles.