Engine Specifications

NOT COMPLETE – (Draft)

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.

BPR7HIX NGK Spark Plug
M14 X 11

Crossover Guide:

Meiya = E6C
NGK = B6HS
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
ND = W2OFS_U

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

Recommended Fuel/Oil Mixture (48cc and 66cc):
Run-in: 32:1
Thereafter: 40:1

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

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 mostly due to fixed timing.

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″ )

Front/Rear mount bolts:  M6 X 1.0 -or- M8-1.25

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 (3)
Clutch cover: m6-1.0 x 20mm (5)
Case mount front: m6-1.0 x 35mm (2)
Magneto cover: m4-.70 x 16mm (4)
Case bolt below the jug: m6-1.0 x 45mm (2 *use flat washers with locks)
Engine bottom case: m6-1.0 x 25mm (1)
Magneto frame mounting m4-.70 x 25mm (4 *use flat washers with locks)
Head studs: m8-1.25 x 102mm  -or-  m8-1.0 x 102mm (4)

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

Woodruff keyways are in 2.5mm and 3mm throughout. New keyways may need to be filed or sanded. A good tight fit is best over a loose fitting connection.

Crank Case Seals
Diameter 1: 1.1cm, 2.2cm
Diameter 2: 1.5cm, 3cm

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