Looks a bit sludgy in the valve chest there. Probably due to infrequent oil changes, which isn't at all unusual in secondhand mowers.
Correct tappet clearances are intake 0.20-0.28mm; exhaust 0.36-0.44mm. Edit: Incorrect; see next post.
So they'll both need a little off the ends of the stems. If you're going to lap the valve faces, do that job first.
Many blokes do this by setting up a guide on a bench grinder, to hold the valve stem at right angles to the wheel face. This method must be used with care, and a vernier caliper to keep tabs on the valve's overall length. It's very easy to take off too much metal!
There is also an 'oilstone method', which doesn't have that risk. But I won't describe it here, as it doesn't work well with ordinary Silicon Carbide [Carborundum] oilstones. Requires an Aluminium Oxide stone.
Points gap is 0.5mm. Data source: B&S 'Service and Repair Instructions'.
Last edited by Gadge; 16/04/15 07:48 PM. Reason: Correction
