This 640 is for 1984–1999 Harley-Davidson® big twin models with large displacement motors with compression ratios of 10.5 - 11.5:1 or smaller motors with 11:1 - 12:1 compression ratio, does not require as much compression as the 631. For hydraulic tappet, spring spacing is required.
These camshafts are also for 1954–’84 big twins with either the Hydraulic Conversion kit or the Cylinder Head Replacement kit for panhead engines. They are also replacement parts for P-Series and SH-Series engines. Since these kits and engines include 1984–’99 style hydraulic lifters, the larger late style roller diameter requires that cams designed for 1984–’99 models must be used to achieve correct valve timing.
In order to achieve stated timing specifications, these cams must be used in engines with 1984-’99 style tappets.
These cams should not be ordered as replacement parts for early S&S SH-Series engines, or for any shovelhead engine equipped with stock valve train. For replacement
parts for these engines, select stock style cams and tappets.