don't worry about tiny flakes of carbon. take an old toothbrush and grind down the stem under the bristles, then put it in the hole with some kerosene. Rotate and brush around. Crank engine over a few times. This creates a powerful action blowig any debris OUT. Now look carefully at the threads from the new and old glowplug. Wirebrush and clean the old one first, and try to reinstall by fingers. If this goes easily, I would look super close at the new plug. If not, I would look super close at the threaded hole with a small inspection mirror ad strong flashlight. NEVER use a wrench to get the plug started, always by hand. This is especially important for things like glowplugs and spark plugs. I learned this many years ago with sparkplugs. Don't ask how
