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...

 I have owned my BMW R75/6 for many, many years now and have always had something of a love/ hate relationship with it.  Get it going well on a long run and all is right with the world, but despite the image that BMW are keen to portray, it has been less than reliable over the years.  I must point out that not all of this unreliability has been BMW's fault.  For example, I have been through two Boyer electronic ignitions over the years, and as mentioned in the story link below, had an oiling fault caused a previous owners attempt to fit an oil pressure gauge (more on this particular fault shortly).  There has been one nagging issue that has been in this bike throughout though, and it bugs the hell out of me. The bike's engine has always made more noise than a bucket load of angry rattle snakes!   I have written about this elsewhere, including here:  Living with a 1974 BMW R75/6 (oldandireland.blogspot.com)  in a story first published in Real ...