spark plug boot sparking
 

i started up my car today and as i was looking into the engine compartment i hear a ticking. sounded like electric jumping so i looked around. i look at the rear trailing, and on the porcelain that is exposed i saw electric arcing between the boot and the middle of the spark plug. does anyone know why this is happening? i tried refitting the boot on the plug but it didn't work.

Re: spark plug boot sparking
 

Electricity acts in accordance to fixed rules, all of the time, every time. So, that arc you see is the path of least resistance between the two points of conductivity involved. Your mission is to make the path have more resistance than the path inside the spark plug. This should be easy because you can see that path is only
.039" long, (about, the spark plug gap).

The boot has been pushed onto a spark plug that was not perfectly clean. Now that arcing has burned a path along the inside of the boot, probably following that dirt path.
once this happens the burned (now carbon) path becomes less resistant than the gap. So the resistance path is not the full length of the plug ceramic but just from the end of the boot to wherever the arc stops on the ceramic. (probably some more dirt). Inspect the plug for filth and cracks. Gap the plug to the shortest gap allowed by the operators manual. (Shortest resistance path).
Now throw all of the wires and boots away and put in new plugs and wires.

Notice now that the typical plugs called out for rotary engines have those big as ground electrodes, and a big fat center electrode. This tends to act like a capaciter and delay the arc formation. This gives the current time to seek out another path as in your case down the side of the boot. It is difficult to visualize a situation where you have parrallel paths where one is over an inch (down the boot) and the other is .039 (the plug gap). But it is obviously the case.

Now notice that more expensive plugs for the same application have fine wire center electrodes and even fine wire ground electrodes vice the big wide ground electrodes. Because they work better in every situation, and arc formation is the very best, and the fastet.

The next step up is a CD system where the rise times are so fast that there is no time for additional paths to develop and current delivered is so high it burns through any dirt or fauling in the gap area.

Lynn E. Hanover