Pull the black rubber plug off the flywheel view port (marked M3) on the engine case.  Use the kick starter to bump the flywheel around until the TDC mark is aligned with the hash mark on the case.

The TDC mark is the arrow WITHOUT the dot at the shaft. The arrow shaft with the dot is used to set the ignition timing. The arrows will be coming into view on the compression stroke.

Before starting, place a catch under the cylinders to collect any oil which may trickle out. Use a 12mm or 13mm (maybe both!) wrench to loosen the valve cover retaining nut.

Remove nut and washer. Be careful as the washer sometimes sticks in the nut recess.

Remove valve cover. Two studs are in the cylinder head to align the cover. Check and make sure these are not loose. If loose, pull and coat end with LokTite and tap firmly back in with a hammer

You can now see the rocker arm assemblies, push rods, adjustment bolts and tops of the valve spring keeper plates

The valve cover gasket is made to be re-useable. Before removing it, mark it so it goes back on the same way it came off. This will minimize oil seepage. It is not necessary to remove the gasket.

These are the cylinder head stud nuts. Check the torque (42 to 45 ft/lbs) BEFORE adjusting the valves, not after as this affects the valve clearance. Loosen each nut 1/4 turn before re-torquing. Use a "cross pattern" when when tightening the nuts.

To make the engine easier to turn over you can remove the spark plugs. I usually do not do this as I find it unnecessary. One less chance to strip the plug threads also.

An easy way to know if you are on the correct cylinder to adjust the valves is if you can easily spin the push rods with a finger tip. If you can't, the engine is set for the other cylinder or you can bring the TDC arrow around one turn.

The left finger is pointing to the valve adjustment screw while the right finger is pointing to the lock nut. There is one each for both valves.

Use a 10mm wrench to hold the valve adjustment screw while using a 13mm wrench to loosen the lock nut. You can adjust either valve first.

Loosen or tighten the adjustment nut so that with the TIP of the feeler gage  (.002 to .004) inserted, the gage will hang freely in place.

If you are adjusting the valves to .004, a .003 gage should fall free and a .005 should not slip in without moderate force if at all.

When satisfied, hold valve adjustment screw steady and tighten the lock nut. Recheck clearance and adjust the second valve.

Wipe the valve cover and gasket clean and replace cover. You can expect to find a small slurry of fines in the bottom of the cover. This is usually valve guide/push rod material.

Replace washer and valve cover retaining nut.

Tighten until SNUG then 1/4 turn.