ORIGINAL: GhostRider32
Yes. The cam has to come out for front or rear bearing replacement. It is easy to set. There is a dimple on the cam gear (inside side of gear, you can't see the dimple when the cam is installed IIRC) that goes straight up when the piston is at TDC. If you even get it off 1 tooth, it won't run right. Just point the dimple straight up and you should be set. If you want to make it easy on yourself, make your own mark on the outside of the cam gear and case while the cam is installed and piston is at TDC. Then line up the marks when re- assembling engine.
The timing for the cam is not straight up! The dot that is visible from the outside when the cam cover and exhaust cam follower are removed, goes in line with the cam followers/ push rods as in the picture. On the OS 91, there is a + mark on the prop drive hub that indicates crankshaft top dead center when aligned with the crankcase seam behind the hub. The gears on the cam are spiral and the cam twists as it is inserted so you will have to allow for the twist and lead the position a little.
