As Mr A. Shapland mentions the “Overfilled Sump Saga” perhaps I could come in on this one too.
Valve burning can be caused by a number of different things, but the use of a fuel with an octane rating higher than the makers stipulate is not one of them, though I do not doubt that Mr Staple) was told otherwise.
Engines — like human beings vary, and in certain cases it can be a definite advantage to do this, as, for instance, when “running on” is a problem. From time to time one comes across engines which arc prone to this fault, and the exact cause may not be easy to pin-point. One may be told that it is simply a matter of using a plug of the correct heat range, but this trouble is not caused by pre-ignition in the normal sense of the word, and changing the type of plug may have no effect.
Using fuel of a slightly higher octane rating, however, will usually very much reduce, and probably eliminate, the fault. To reverse the procedure and use a low octane fuel in a high compression engine can of course lead to trouble and should not be done, but most people I think are aware of this.
Bridlington A.C. Savile