Over time, wear patterns do emerge with all engines. With an O.S. four-stroke engine, some wear on the cam lobes is to be expected after long-term use. Replace the camshaft.

To time the camshaft, you line the dot on the cam gear with the center of the cam follower when the piston is at top-dead-center.

It's normal for swirl marks to appear on the rear cover of nearly all single-cylinder model engines, 2 or 4-stroke.

The mounting pattern for the O.S. FS-120 Surpass is the same as for the 1.40 RX, but not the 1.60 FX.