1999 Sentra: Fixed blown out Spark Plug

[mark_gober]

Hey everyone,

I'm new to the Sentra Forum, but I usually post on the Windstar forums. I wanted to share a technique that I'd used to repair my dad's Sentra.

He owns the 1999 Sentra w/ the 1.6l engine. He called me the other day saying that he was driving to work and thought that he'd had a blowout because he heard a loud bang. He said the engine started running terribly and was loud. He pulled over and looked and his #1 spark plug had come completely out of the engine (and was still connected to the wire). He limped it to work and called me. He assumed that the engine was toast and that it had suffered some catastrophic fatality and wanted to borrow my spare vehicle.

When I went over to check on it, the spark plug's electrode was pretty smashed and I assumed it had made contact w/ the cylinder. (Other things have caused me to question the honesty/mechanical aptitude of the previous owner...It was not out of the question that he'd installed the wrong plugs) When I started looking at the plug hole down in the head, it appeared to be in fine working order and still had threads. (In other words, no catastrophic damage)

I decided that we could probably fix the problem by re-tapping the plug hole or, at most, replacing/repairing the head. Cheapness won out and I bought a tap from Autozone. They have two types. One is a double ended tap that will fit two different sizes of spark plugs. It won't work. While it is big enough to go down the hole, the socket that drives it is too big to fit down the hole. I went to Autozone and purchased a spark plug tap specifically designed to for tight clearance situations. Instead of being driven by a socket, it's driven by a ratchet extension.

When I got home with the extension (and the required anti-seize), I tried to tap the hole. I was having fits getting the tap to bite. It requires downward pressure, but because I was using an 18" extension and a ratchet, it was pretty wobbly. Everytime I felt like it was biting, it was wobble and break free. Fearing that I'd permanently damage it, I stopped and devised a plan.

I needed to stabilize the extension down the tube so that it wouldn't rock around. After poking around my garage looking for the magic ingredient, I saw a tube of paper towels. I had an "ah-HAH!" moment. I took paper towels and inserted them down the spark plug hole beside the extension. (making sure that the extension was centered in the hole). After each towel went down, I tamped it down with a long large flathead screwdriver. After getting four paper towels down the hole and sufficiently tamped, any and all slack/wobble was gone. The extension was rock solid now and I could focus on downward pressure rather than stabilizing the extensions. The tap bit first time and I was able to run it all the down.

I pulled the towels out with the same screwdriver and the extracted the tap. Using a flashlight, I found no shavings in cylinder (they got caught by the anti-seize on the tap). I threaded the plug back in there, put new plug wires on it and fired it up. It worked like a champ.

To address the obvious question...how did it come out of the hole? I can only surmise that whoever put it in there last time, didn't properly torque it down and it slowly backed its way out of the hole. Once it got to the last thread or two, the cylinder pressure was high enough to rip it free from the last two threads. Cylinder two and four were not tightened either. They weren't more than about 1/2 of a revolution from being tightened, but they certainly weren't tight.

Anyway, I just thought I'd pass my paper towel idea on to everyone. Those inline fours with the deep inset spark plugs can really make it difficult to work on the spark plug holes. Hopefully this'll help someone down the road.

Mark

[Airjer_]

These are the best spark plug thread chasers. They work by inserting them in the hole, tighten the thumbscrew, and then turning them out of the hole. Since they start at the bottom where the threads are usually in much better shape you get them started right away. The shank of the tool also helps center it as you get the tool started and while your backing out of the hole.

[mark_gober]

Originally Posted by Airjer_

These are the best spark plug thread chasers. They work by inserting them in the hole, tighten the thumbscrew, and then turning them out of the hole. Since they start at the bottom where the threads are usually in much better shape you get them started right away. The shank of the tool also helps center it as you get the tool started and while your backing out of the hole.

Yeah,

I looked into some of those, but ran into two issues. First, I couldn't find them locally. Next, the cheapest I could find them was $40 on ebay. Sears was selling them for $80. They might be the best tool ever, but I'd have a hard time paying $80 for it. Before I'd pay $80, I'd pull the head off and run a regular tap backward through the hole.

Whoever invented that tap though, is a genious. Frankly, all taps should be that still.

Mark

[danielsatur]

Spark plugs should always be replaced when the heads are cold!