The original knucklehead cylinders were weak and had a tendency to crack between the mounting flange and the bottom fins. It is this weakness that can cause a problem if you sleeve an original knucklehead cylinder. You may wind up with a cylinder that "pogos" on you.

What happens is the cylinder cracks all the way around and, as a consequence, the bottom section of the cylinder attached to the mounting flange remains attached to the crankcase. The top half separates from the bottom half and slides up the sleeve. The result is that the cylinder head bangs into the frame and, of course, your Harley quits running.

There is another problem with sleeves. If you set a standard ring gap the piston may seize. Heat does not transfer as readily from a sleeve to a cylinder as it does through plain gray cast iron. Ergo, the rings swell up or expand in the cylinder from the excess heat and, when the ends of the piston rings (at the gap) ram into each other, the piston quits moving.

If the piston seizes on the way up the cylinder this can also cause cracking of the cylinder between the mounting flange and the bottom fins. A cast iron sleeve will not even transfer heat properly to an aluminum cylinder.

It’s cheaper, in the long run, to do it right to begin with. If you don’t have the time or the money to do it right, when will you have the time and where will you get the money to do it over?