I have a 1994 Nissan Sentra, 1.6L 4 cyl. It started running rough and when I looked at the engine I noticed that one of the spark plugs was about half an inch higher than the other 3. It does not screw all the way down into the engine. I removed the plug and found that it was badly burned and it looked like the center pole of the plug had moved. I replaced the plug and the car runs fine now but the new plug also does not screw into the engine. It is about half an inch higher than the others. My guess is that the threads are stripped in the engine. Will I damage the engine if I continue to run it with this spark plug not fully seated?
They make “Thread Chasers” for spark plug holes. It’s a special purpose tap made to repair damaged threads. Purchase the correct one and use it to restore the damaged hole. Chances are, the lower part of the threads are just fouled with carbon which will clean out with the tool. Put some grease on it to catch the chips so they don’t fall in the engine.
Go to a local auto parts store and ask for a sparkplug thread chaser. About $12.00. And run the proper size down the sparkplug hole. Reinstall the sparkplug.
I put grease on the threads of the chaser, the grease captures debris. You really want to make sure you dont come in contact with the top of the piston with the thread chaser, I just want to make you aware of this. If you can take a look and make sure there is not a heli-coil or a insert already in the hole. I have seen chasers/insert taps driven into piston tops and have seen people try to cut new threads in a insert. You end up cutting to top of the insert off and screwing it into the cylinder,not a good idea.
Follow Caddyman’s advice…ASAP!
Otherwise the plug may blow out of the hole and take the top half of the threads with it. Then you’ll be adding a helicoil.