Here you go, all nice and easy to read.
Oil tank capacity is 3.6 quarts (U.S.) (3.4 liters)
ENGINE OIL
Use the proper grade of oil for the lowest temperature
expected before the next oil change.
If it is necessary to add oil and Harley-Davidson oil is not
available, use an oil certified for diesel engines. Acceptable
diesel engine oil designations include CF, CF-4, CG-4 and
CH-4. The preferred viscosities for the diesel engine oils, in
descending order, are 20W-50, 15W-40 and 10W-40. At the
first opportunity, see a Harley-Davidson dealer to change
back to 100 percent Harley-Davidson oil.
See 1.5 ENGINE OIL AND FILTER for all service information.
Table 1-4. Recommended Engine Oil Viscosity
HARLEY-DAVIDSON TYPE/ VISCOSITY HARLEY-DAVIDSON RATING/ LOWEST AMBIENT TEMPERATURE/ COLD WEATHER STARTS BELOW 50°F(10°C)
HD Multigrade / SAE 10W40 / HD 360 / Below 40° F (4° C) / Excellent
HD Multigrade /SAE 20W50 /HD 360 / Above 40° F (4° C) / Good
HD Regular Heavy /SAE 50 / HD 360 / Above 60° F (16° C) / Poor
HD Extra Heavy /SAE 60 /HD 360 / Above 80° F (27° C) / Poor
I'm sure you can find the 20w-50 in motorcycle oil, don't use automotive oil, too many detergents.