I actually had that same problem when I put my 493 together last winter. I also did what Al said but it did not fix it as mine was tight enough that I had to force it in which was a no no. I ended up taking all the bearings back out except the #1 and 5. Cam went right in so I put the bearings back in one at a time intil I found when I put #3 in the cam would not go all the way in. After I saw scratches on the back of the #3 cam bearing I saw where a piece of casting right next to the #3 bearing hole had laid over into the cam bearing hole and it was going in the front part of the bearing hole so that it stayed there when I drove the bearing in and it was raising the bearing shell just enough to cause the problem. I used a file and filed it off and ran a hone thru the cam bearing hole. Installed another bearing and all was fixed ! Ron