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Spark Plug Rotation Chart

The spark plug's firing polarity causes uneven electrode wear. The magneto sends a positive voltage down one lead and a negative voltage down the next lead and so on . Each ignition lead always fires the same voltage (on horizontal-opposed engines.

For a six-cylinder engine move plugs

1T to 4B
2B to 3T
1B to 4T
2T to 3B

Where T=top and B=bottom and the number is the cylinder position number.

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