May have already been addressed but I got tired of reading responses. Prior to installing the bearings I like to use an 1/8" mandrel, long enough to reach the center cam journal with some medium to fine sandpaper in the slot on the end. Pre polish the cam bearing bores in the block to remove any burrs that might cause the bearing to shrink in the bore. Obviously don't remove too much material or the bearings won't have sufficient press to stay in the block. I like to take the leading edge of the cam bearing and knock the edge between the chamfer and the outer bearing surface down. It looks like the chamfer should be enough to prevent metal from pulling off the bearing, but it isn't. I take a razor blade or bearing knife and just lightly chamfer the leading and trailing edges of the bearings. I've seen a few bearings with a slight edge on them. I still end up on a few engines having to run the sandpaper mandrel through the bearings themselves. Done the cam with the diagonal slots cut into them. That's the last thing I do if nothing else works and then use some green scotch brite on the mandrel to polish the bearings and make them look new again. Also, once the cam is installed, if it spins freely through part of the rotation but gets tight partway through, it's a camshaft problem. Try a different cam. This is such a problem that at the shop I worked at we would install cam bearings in the block first and make sure the cam fits before any further assembly was completed.