The Harley-Davidson Shovelhead engine requires different oil types depending on modifications.
Harley-Davidson’s Shovelhead engine, produced between 1966 and 1984, was the predecessor of the modern-day Evolution engine. Initially offered with a displacement of 73 cubic inches, by the end of its production run in 1984 it had a displacement of 82 cubic inches. Oil specifications for all motorcycles built with Shovelhead engines between 1966 and 1978 are the same. Stock valvetrains require a higher viscosity oil than is listed in the Harley-Davidson owner’s manual. Screamin’ Eagle oil is Harley-Davidson’s preferred oil and is available from your local Harley dealership.
Stock Harley-Davidson Shovelhead Engine: 1966 to 1978
Use 4 qts. of 25W-60 weight oil in stock Shovelhead engines built between 1966 and 1978. Avoid using automotive oil, as specialty motorcycle oil has specific weight properties necessary for twin-cylinder engines to run properly. Using Harley-Davidson’s Screamin’ Eagle oil is recommended.
Modified Harley-Davidson Shovelhead Engine: 1966 to 1977
Use 4 qts. of 25W-50 weight oil for engines that have had minor or major modifications to either the valvetrain or pistons. The 50-weight oil is also recommended for stock Shovelhead engines in cold climates or in high altitudes.
Stock Harley-Davidson Shovelhead engine: 1978 to 1984
Stock Harley Shovelhead engines built after 1978 require 4 qts. of 20W-60 oil, even though displacement on these engines was increased. Use 25W-50 oil if you live in a high altitude, such as Denver. Hotter climates, such as in Arizona, require the use of thicker oil, such as 70-weight oil.
Modified Harley-Davidson Shovelhead Engine: 1978 to 1984
Modified Harley Shovelhead engines produced after 1978 still require 4 qts. of 25W-50 oil. Use a lighter-weight oil for these engines to optimize performance.