Kawasaki G31M

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Kawasaki G31M
Also called Centurian
Production 1970 - 1971 (4490 total produced)
100cc rotary valve single cylinder two-stroke
Top Speed 65 mph
Horsepower 18.5 hp @ 10,500 rpm
Recommended Oil K-tech 10W-40
Related Kawasaki F21M

The Kawasaki G31M "Centurian" was a 100cc, 2-stroke, off-road motorcycle manufactured by Kawasaki from 1970 through 1971.


In the early 1970s the highly tuned G31M was a dominate force in Flat Track, Tourist Trophy and some motocross racing along with its larger brother the 250cc Kawasaki F21M. This model consistently dominated the 100cc class with its unheard of 18.5 horsepower rated engine. The small tip or "stinger" on the expansion chamber gave the Centurion a distinct sound that is unmistakable to this day. The engine case was slightly different than other Kawasakis with the G31M having a secondary air intake on the carburetor cover. It also required the use of bean oil as a fuel additive for lubrication.

Only 4490 units were made in 1970.

1970 Steve McQueen Kawasaki G31M Centurion "Ringadingdoo" in orange

Steve McQueen Centurian[edit]

Actor Steve McQueen was given six G31M bikes by Kawasaki for use during the filming of the motion picture, Le Mans in France with one remaining at Santa Paula airport. When McQueen returned from the filming, he had the Kawasaki green painted over in orange, striped it in gold and gave it the name Ringadingdoo presumably a reference to the noise made by an un-silenced race-tuned two-stroke. McQueen used the Kawasaki for trips to the coffee shop and visiting friends' hangars. The bike sold at auction for $55,575 in November 2007.


G31M Crank Assembly
G31M Rotary Disc Valve
  • 100cc
  • 2-stroke, 1 Cylinder
  • Rotary Disc Valve (steel instead of pressed fiber. Original part: #12001015)
  • 5-Speed Return Shift
  • Maximum Horsepower: 18.5 HP @ 10,250 rpm
  • Spark Plug: NGK B9HV
  • Tire Size
    • Front: 3.25-18 4PR
    • Rear: 3.25-18 4PR
  • Color
    • Fuel Tank: Lime Green
    • Front Fender: Aluminum
  • Engine No.: G31E00001-
  • Frame No.: G31-00001-
  • Parts Catalog No.: 99995- 113 plus 99995-175S
  • Shop Manual No.: 99995-201 (SM-1)
  • Remarks: Motocross type version of the G3TR. The carb cover on the 1971 Centurian had an air filter unique to this model allowing extra air intake.

Photo gallery[edit]

1970 Kawasaki G31M Centurion in Lime Green
1970 Kawasaki G31M Centurion in Lime Green
1970 Kawasaki G31M Centurion in Lime Green
1970 Kawasaki G31M Centurion in Lime Green