Engine Specifications


The 66cc/80cc China Girl two stroke engine is a simple design with very few moving parts and is an easy engine to upgrade for speed and reliability. These engines are very easy to work on and if modifications are done correctly they can produce at least 9 horse power.

Simple modifications can produce a good 4 horse power engine but more specifically and important, a good modified engine can be dependable when built correctly and maintained properly.

Speed is great but reliability has it’s own merits. By working on and maintaining your own engine you can expect to to learn something new while having fun and save a ton of money on simple and even a major repairs. Below are some common specifications for the 66cc Two Stroke China Girl, I hope they help you with your project. If you have any questions please feel free to contact me.


Cylinder Stud Torque Specifications:
6mm studs – 10-12 ft/lb.
8mm studs – 13-15 ft/lb.
8mm x 1.0mm studs – 14-16 ft/lb.

Head Gasket: .72mm
Base Gasket: .98mm Add extra for open porting.


Recommended spark plug (48cc and 66cc):
Stock plug is a NGK B6HS
NGK B7HS= (colder) NGK B5HS= (hotter)
The NGK B5HS should be used in extremely cold weather and the NGK B7HS in extremely hot weather. NGK B6HS is the correct stock replacement plug.

M14 X 11

Crossover Guide:

Meiya = E6C
Denso = W14S
Denso = IFT-16
Champion = L86C
Champion = CJ7Y
AC = 42F
Autolite = 414
Autolite = 425
Autolite = 4093
Bosch = W6AC
E Spark Plug = E3.12
NanJing = Z4C
Wei Xing = Z4C
LD = Z8C
Bosch = W9EO

Spark Plug Gap (48cc and 66cc): 0.6mm, (0.024 – 0.032″) Depends on conditions

Recommended Fuel/Oil Mixture (48cc and 66cc):
Run-in: 24:1 – Use 1 gallon and easy riding.
Thereafter: 32:1

Compression Ratio (48cc and 66cc): 6:1 – Approx. 95 PSI Stock

Compression, (measured / Ideal):
48cc: 125 psi
66cc: 115 psi
Maximum is 150 psi otherwise damage could happen.

Squish Band Clearance: (49cc – 80cc) 0.6mm ~ 0.8mm

Lateral Play .028

Max Power:
48cc: 1.2kW, (1.6hp), @ 5500rpm
66cc: 1.7kW, (2.3hp), @ 5500rpm

Bore x Stroke:
48cc: 40mm x 38mm
66cc: 47mm x 38mm (69cc = 47mm X 40mm)
N.B. Capacity = pi * (Bore/2)² * Stroke. e.g. pi * (4.7/2)² * 3.8 = 65.9cc. (Calculate in cm.)

Overall Weight:
48cc: 9kg
66cc: 9.5kg

The 66cc two stroke china girl engine has two different front mounting bosses and come in the following dimensions:

41mm ( 1.614″ )

51mm ( 2.007″ )

Generally, the maximum power that these engines develop is in the 5,000 to 6,000 rpm range. At higher revs the power tapers off.

For mounting, many of the engines come with 6mm bolt studs although there are some configurations that will use an 8mm bolt studs. Be sure and ask your vendor what their specific dimensions are to insure you are getting the correct configuration for your application.  This is also good advice if you are ordering custom mounts.

Sprocket cover: m6-1.0 x 25mm
Clutch cover: m6-1.0 x 20mm
Case mount: m6-1.0 x 35mm
Magneto cover: m4-.70 x 16mm
Case bolt below the jug: m6-1.0 x 45mm
Head studs: m8-1.25 x 102mm

Wrist bearing: 10X14X13
Main bearing:
Crank & Transmission Bearings: 6202RS C3