Spark plug wear

[stevieturbo]

Query as to why this happens.

2 plugs, taken from the same engine ( Evo in this case ), but the 2 plugs have quite opposite wear characteristics.

Ive also seen this on Subaru engines. 2 plugs wear one way, the other 2 the opposite.

Can anyone explain why it happens ??

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[ssray]

You may have a waisted spark system like on bikes, on one plug the spark jumps from the center electrode on the other it jumps from the outside to the center electrode.
Ray

[Malachy]

er thats not wasted spark :/
wasted spark is when a "spark is wasted"
basically it works as a 4 cylinder engine only having 2 sparking points so you have
coil a
and
coil b

coil a fires and gives a spark to both cylinder 1 and 4, as only one of the cylinders will be ready to fire (since it takes 720 degrees for a 4 stroke to prep the combustion chamber for ignition) then only 1 or 4 will fire depending on the state of the engine.however whenever there is a spark at cylinder 1 there will always be a spark at cylinder 4 aswell, even though only one of them will be firing, thus meaning one of the sparks is "wasted" hence "wasted spark"

coil b gives a spark to both 2 and 3 and works as above

[GreenV8S]

I think you're both right, in a way.

With a wasted spark system, two plugs spark at the same time because they're connected in series via a single coil. The current flows in the opposite direction through each plug i.e. for one plug the center electrode is positive, and in the other it is negative. I don't think there will be any significant difference to the way the spark forms, but there may be some electrolytic corrosion going on and this would obvious affect the electrodes asymetrically.

[eliot]

Edis (fords wasted spark system) has been in use for an entire decade.

[Pigeon]

GreenV8S said:

I think you're both right, in a way.

With a wasted spark system, two plugs spark at the same time because they're connected in series via a single coil. The current flows in the opposite direction through each plug i.e. for one plug the center electrode is positive, and in the other it is negative. I don't think there will be any significant difference to the way the spark forms, but there may be some electrolytic corrosion going on and this would obvious affect the electrodes asymetrically.

Metal atoms prefer to form positive ions rather than negative ions, so there is a tendency to transfer metal from the positive to the negative electrode. Same with DC arc welding - though there are exceptions, generally you make the rod positive and the workpiece negative.