Re: Mark 20 with bendix ign problem

[Mark Bartlett]

so my question is how do we know what the engine is set up for positive or negative earth . I have put a volt meter on 20 volt scale positive to block and negative to plug wire and the needle swings both ways so I still dont know if its wired correctly. back when this motor was built they used alot of positive ground systems I have hooked the red wire to the points and blk wire to grd. The spark jumps a 100000 gap .

Why then do we worry about coil polarity? Because the spark plugs do care which way the electrons are flowing in the high tension circuit. The spark plug has a thermally insulated center electrode (surrounded by ceramic). With engine running the center electrode runs substantially hotter than the exposed end electrode. Design of the ceramic insulator determines how hot the center electrode will run, leading to the designation of hotter or colder spark plugs. As electrons go, they love to jump away from a hot surface and fly toward a colder surface, so it is easier to drive them from hot to cold rather than from cold to hot. End result is a difference of 15 to 30 percent in voltage required to make spark "initially" jump the gap on the plug depending on which way it is going. So the spark plug prefers to see a voltage potential that is negative on the center electrode and positive on the end electrode for the very first hop of the spark.