Plugged spark plug holes

67Dart273 said

Even thread chasers can leave small chips here and there. Don't just use a plug as suggested. It does not cut and may damage the threads because it can compact the material that has built up and "jam" the threads.

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Well it's either one or the other. I wouldn't use a tap only as a last resort. Plug thread chasers are designed for this particular use. The modified plug is a last resort before you pull the head and clean the threads with a thread chaser. :BangHead::BangHead: