It is (IMO) a good idea to check the tappet clearances on any 4 stroke engine you acquire, as part of your first definitive tune-up. Checking is easy on the side valve Briggs, but adjusting is difficult. Fortunately, on side valve engines you seldom need to adjust, unless something has gone wrong.

All that is required is to remove the two screws from the valve chest cover and carefully remove it, in the hope of not damaging its gasket. You then rotate the engine to a position just past top dead center on the compression stroke (later Briggs manuals say rotate it until the piston has moved 1/4" back down the bore, on the expansion stroke, which is a good way to do it). You will see where you need to make the measurement, in the tiny gap between the top of the tappet and the bottom of the valve stem, which is just below the bottom of the valve spring. Slide a feeler gauge (a thin strip of hardened steel) of the required thickness into that tiny gap. You can see which valve is which by looking at which port is above that valve. One will be directly under the exhaust port, the other directly under the inlet port.

The required clearance for the inlet valve is 0.005-0.007". For the exhaust valve it is 0.009-0.011". You need a fairly sensitive touch when you push the feeler gauge in, because lawnmower engines have very weak valve springs, and you can easily force a thick feeler gauge in just by pushing on it. Just keep increasing the thickness of the gauge until you can feel a slight drag on it as you slide it back and forth. When you feel that drag, you have gone 0.001" too far.

While you have the valve chest cover off, turn it over to look at the back of it, which is normally inside the chest. You will see the breather valve attached to the cover. Wash it in petrol or kerosene in case it is gummed up due to the sustained overfilling with oil.
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