Itinerant Air-Cooled

Reid wrote: Three of four cylinders were right at 135 psi, #3 has 80.
valve stem heights all seem to be right on.
Could the rod bearings be worn enough to cause the lower compression?
good oil pressure (idiot light),
Ideas?

Count each valve adjuster's threads sticking out past the lock nut. Where does #3 fall in relation to others?

You can devolve into a frenzied anxiety about your engine's slow death, but if you have decent oil pressure, decent temperatures, decent running, then drive it . . . decently sensitive to its semi-geriatric condition. Keep an eye on #3.
Colin
(connecting rods have nothing to do with compression)