The sleeve has been pressed into the existing oil passage. The case is notched (S&S Cases come with the notch in the case). A new hole is drilled in the side of the spigot (as per S&S Instructions) to continue oiling the piston skirt. Hole is deburred. The oil now flows from the top end - down the original hole in the cylinder, past the original hole to oil the skirt(blocked by the sleeve), into the notch in the case, and out through the new hole in cylinder spigot to oil the piston skirt, since the piston is now going lower than it originally did with the stock stroke - so the oil ring on the piston doesn't get in front of the original hole and suck oil and cause it to smoke like it's on fire or something. This modification is only one part of the process. All this for a few extra cubic inches. Still want a Stroker? The answer is YES !