The recent discussion about spark plugs reminded me of an admonition I
had read in the factory manual for my 1959 Mercedes-Benz.
The factory had approved three brands, Bosch, Beru, and Champion
as functionally similar. However, the following additional information
was given, and I quote:
"On Champion spark plugs the beginning of the thread is not
chamfered, so that the free thread length is slightly longer than that of
Bosch and Beru spark plugs. For this reason it is necessary to install a
second sealing ring of a minimum thickness of 1mm when Champion spark
plugs are used. This is necessary, since otherwise part of the plug
thread would project into the combustion chamber and may accumulate
carbon deposits, which, may damage the thread in the cylinder head when
the plugs are unscrewed."
My Mercedes is a 219b, an originally-inexxpensive sedan, but has
an aluminum cylinder head which could easily be damaged in the above
The moral to the spark plug discussion and in light of the
warning by Daimler-Benz is to be sure that the plugs being installed are
functionally and dimensionally similar to the factory requirement.
I use Champions in both of my MGBs, but I use Bosch in the
Mercedes. Perhaps it's well to use plugs manufactured by folks who speak
the same language as the manufacturer of the automobile.
Charles E. Edwards, CPA
Virginia Beach, VA