Where the valve seats against to seal it off when the valve is closed.
There is only one cam, to get it out you have to split the block.
To pull the valves out to clean them up, take the head off, exhaust off and that little side plate off.
Then use a flat head screwdriver to push the round disc bit that holds the spring on off to the side so that it will pop out.
To put the valve spring back in, fully compress the spring and hold it compressed with cable ties, put that, the valve and the top disc bit back in, make sure the disc is centered and cut the cable ties.
Please forgive me for insight on my dodgy backyard jobs, where I have los the "proper tools" and just find alternatives that "work" as such.
