Just changed the factory plugs today in our Explorer. Quite easy, just had to disconnect a couple vacuum lines and one of the intake tubes. All plugs came out pretty easy, although cylinder #3 seemed just a tad looser than the rest. Anyway, the factory gap should be .027” - .031”. All 4 plugs were between .031” and .033”. Not too bad. The new Motorcraft SP-550 plugs I installed were all bang on .029” out of the box, right in the middle. The old plugs look like they could have gone farther still, aside from a couple being over the recommended gap. What do you think?