Has anyone heard of this? When rotating the motor by hand the rear piston Get really tight when it comes up top dead center and knocks. Any idea what this could possibly be? S&S 97 big bore kit with high lift springs and tw 54 cam.

 

Tell us more! Have you just built this and are yet to run it? When turning over by hand we have to open the valves, against the valve springs, which will feel tight, however there shouldn't be any knocks IMHO.