I went to replace the sprocket and needle bearing on the 6401, and discovered that the bearing (or at least the metal sleeve housing the bearing) seems to be tightly press-fit into the clutch cover. It looks to be a different bearing design than the parts list and the service manual I have, both of which show an exposed cage rather than a sleeved one and no special tool required to remove it. (Same as my 359.) I think I saw indicated somewhere that the original design was now obsolete. Is there any secret to removing it other than brute force? A dowel and a hammer? Luckily it doesn't seem to be all that important, as I guess it only spins at idle, and the current one seems serviceable. I just figured I'd change it while I had it apart. I also picked up the piston bearing to replace when I swap the top end, but it looks like I may have the same issue there. Hope to finally unleash this bad boy this weekend, milling some poplar siding. If it goes well I'll do the upgrade to 84cc, and compare.