As mentioned last time, when rebuilding the top end of my R75/6 the replacement heads that I had for it had a few problems. The heads are from an R75/7, so are a straight fit onto my bike because I already have modified the  valve gear to a later specification than that originally fitted to my series 6 bike.  I have no idea of the mileage these heads have covered, so they were stripped for inspection and cleaned before anything was done with them.  I have a small lever type clock gauge which I used to check the valve guides for wear.  These at least were well within tolerance, so we had a good start. Next the valves.  Both inlet valves looked good and a light lap in with fine paste produced a good seating surface.  The exhaust valves were a different story.  They appeared to have been seating on a knife edge thin ring around the valve (see the before and after picture below).  When running my finger nail across this, the nail actually clicke...