Models and Motor Sizes.
(This is a clipping from the Harley Spare Parts Book)
When ordering parts it is necessary to specify the correct model so that the parts for that model will be supplied. In case of doubt, refer to the motor number stamped on the left crank case. The part of the motor number before the letters indicates the year, and the letters the model of the motor. Example: 21JD13561 is a 1921 model JD, 30V1697 is a 1930 model V. Sidecar or tuck models are indicated the same way in the chassis number shown on the rear frame tube. Example: 30MW6587 is a 1930 model MW.
Model A is a magneto equipped 21" side valve single.
Model AA is a magneto equipped 21' overhead valve single.
Model B is a generator equipped 21" side valve single.
Model BA is a generator equipped 21" overhead valve single.
Model C is a generator equipped 30.50" side valve single.
Model CM is a magneto equipped 30.50" side valve single.
Model D or R is a 45" side valve, low compression twin.
Model DL or RL is a 45" side valve, high compression twin.
Model DLD or RLD is a 45" side valve, high speed twin.
Model F or FE is a magneto equipped 61" twin.
Model J or JE is a generator equipped 61" twin.
Model FD or FDCA is a magneto equipped 74" twin.
Model JD or JDCA is a generator equipped 74" twin.
Model V is a generator equipped 74" standard compression twin.
Model VL is a generator equipped 74" high compression twin.
The letter C when used after the model F, J, JD, or V indicates a heavy duty commercial truck motor.
21 cubic inches = 350 cubic centimeters.
30.50 cubic inches = 500 cubic centimeters.
45 cubic inches = 750 cubic centimeters.
61 cubic inches = 1000 cubic centimeters.
74 cubic inches = 1200 cubic centimeters.
The last two figures in the part number designate the year the parts were first used. Common bolts, nuts, washers, etc., are covered by part numbers beginning with (0); such as 062, 0108, etc.