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Down thru the years China bike engine factories have always advertised their biggest engine as 80cc 

 

for that reason, we have elected to listed them the same way. Also by western standards the volume of the engine head combustion chamber is not figured in the engine’s displacement rating, nevertheless some Chinese factories do include this volume in their engine displacement ratings therefore making the engine appear bigger than it actually is.

However, the bore and stroke of an 80cc being 47x38mm only equals 66cc. 

 

To figure displacement for this example:  47mm bore x 38mm stroke; we use a standard formula to figure an engine’s cc displacement; ( multiply 3.142 x radius of bore mm squared x stroke length mm divided by 1000. )

 

Bore diameter divided by 2 = 23.5 mm radius 

To square radius multiply 23.5mm x 23.5mm = 552.25 radius mm squared

552.25mm x 3.142 = 1735.17mm

1735.17mm x 38mm = 65936 cubic milliliters;

To get cubic centimeter divide 65936 by 1000 = 65.936cc or round off to 66cc.

 

As a result we see there is no such thing as a 80cc:



 
Gen-II

Gen-II  50cc only; 40 x 40mm bore & stroke  

Steel lined cylinder wall:                     
45 degree angle fire head;                       
203 crankcase bearings;                        
Needle bearing on piston wrist pin standard;
Improved carburetor design:                   
EPA approved with catalytic muffler
USA EPA approved for off road


 
Gen-II-A

Gen-II-A 58cc;  43x40mm bore & stroke     

Chrome lined cylinder wall:                  
45 degree angle fire head:                        
203 crankcase bearings; Bushing pin.                        
Bushing piston pin std. / Needle bearing optional; 
Standard NT carburetor with intake tube:                    

Catalytic muffler EPA approved:
EPA sticker on engine effective Jan. 2008:
USA EPA approved for off road use

GT4


66cc Old style GT4   47x 38 mm bore & stoke;

Center spark plug head;                       
Small bearing 202 crankcase bearings;                        
Bushing on piston pin std. / Needle bearing optional;
Old style NT carburetor design:                   
Black Catalytic muffler EPA approved              
EPA sticker on engine effective Jan 2008
Same size engine as was previous called 70cc or 80cc
USA EPA approved for off road use