Cross-threading is where you don't properly align the threads of the plug with the pre-existing threads in the block. You'll force the plug to spin into the block, and cut new threads or cut across the existing threads. As SMF834 says, that's bad news for your block. There's no easy fix for it.I have some questions, if you guys can answer them, i'd appreciate it.
1. It says "Install the new plus being careful not to cross thread them. Then tighten to 13 ft lb of torque."
What does cross-thread mean?
excuse the noobness.
A trick I use (not just on plugs, but with threads in general) is spin the bolt backwards until I feel it "drop" into place. This is very slight, especially on fine threads, but will happen within 1 revolution. This means that the first thread on your bolt has lined up with the first thread cut into the block, or where its groove starts to thread itself in. Then, you know that you are threading back in along the same line of the threads that are already cut in the block.
If it doesn't spin along the threads freely, and it is hard to do, you have a problem.