45" Flatheads (1937 to 1973)


W - Standard Low Compression

WL - High Compression

WLA - Military (USA)

WLC - Military (Canada)

WLD - Sport Model

WR - Factory Racer


G - Tricycle

GL - Tricycle

GA - Tricycle w/o Tow Bar

GE - Electric Start (1964 to 1969)

5A - Electric Start (1970 to 1973)

45 Flathead

1 - Bore, stroke, pistons, rods, crankpins, flywheels are the same for all years.

2 - On engines up to 1939, the forked rod was rotated to be the front rod, to correct oiling problems. On 1939 and later engines, the forked rod is the rear.

3 - There is a number stamped on the side, of the aluminum heads, for compression ratio. A 5 is a low compression head, and a 6 is a high compression head.

4 - Any Sportster distributer or magneto will fit a 1937 to 1973 45" with no modifications.

5 - You may want to update the carburetor with a Linkert M-88, or other 1-1/4" Linkert. The Tillotson carb came out on later trikes, and can be used as a replacement. This update requires a solo (1936-52 WL, WLA) manifold.

6 - Beware of using 1936 and earlier flywheels in later engines, as the oil holes and keyways are different.

7 - WLA's made, beginning in 1941 through 1945, had their serial numbers begin with 42WLA?????. The case production number indicates the correct year of manufacture. Also, there were seven different configurations of 42WLA's, during these years.

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