Here's one to remember....

After doing a rebuild on a xr600r for a friend of mine, as we finished assembly and prepared to replace the valve cover, we did not have a gasket. Local shop said it would be a week to get one in. Excited about getting it running, we thought there would be no harm in installing the valve cover with a good bead of honda bond, instead of the gasket. In fact. in some areas, mechanics prefer the honda bond over gaskets. 

Well, when we tightened the valve cover to spec, the engine would not turn over,.......loosen the cover, it would turn over fine. Turns out that the thickness of the gasket is required to allow clearance on the center journal of the cam, which is not a bearing surface btw. Without the gasket, the valve cover is pinching the cam at the center journal. I guess you learn something every day. Anyone ever experience this?  Took some head scratching to figure this out, as none of us were thinking gasket, and we really didnt know what was causing the engine to tighten up like this.

SP, had I known that the gasket was needed, I would not have installed the cover without one.

We ended up making the gasket from a sheet of Fel-pro (gasket material), the bike started on the first kick!