These 3-7/16" +.010" bore pistons fit 1941-'78 74" HD® big twin OHV engines, producing 8:1 compression with stock unmodified cylinder heads. The modern alloys used in these pistons, coupled with the advanced skirt profiles, allow them to be fit tighter resulting in low engine noise and long engine life. In the past, this could only be achieved with weaker cast pistons.
S&S® will fit these pistons to your existing cylinders (when purchasing new cylinders, pistons can be fit to them as an option)
Since many older motorcycles have been modified, be sure to confirm that your engine is still
stock before ordering replacement pistons.
Using 80" pistons with 74" (331/32" stroke) flywheels will result in very low compression and
poor performance. Using 74" pistons with 80" (41/4" stroke) flywheels will result in contact
between piston and cylinder head, and potential engine damage.
S&S offers machine shop services through the S&S Service and Speed Center®. New pistons can
be fit to existing cylinders for a reasonable charge