Sleeves need to be installed in the F2 cylinder head in order to use it on a K cylinder. Sleeves are installed in 4 of the cylinder stud holes as they are open to the atmosphere on the F2 head. The F2 doesn't use those four holes for oil return but on the K head they are used as oil return. If you dont sleeve them then you have four open holes in the head that can allow water and dirt to enter into the crankcase down through the oil return drains in the K cylinder. Oil can also migrate back up through and they you will have oil mist and leaks. Jay did the work on my head and it is working perfect.