Stripped Spark Plug Threads?

[gabelossus]

I see some posts already pertaining to this issue...hopefully I can get some help with my exact situation. So, I was replacing the plugs and wires (@123k mi) the other day and only had time to do the driver's side at the moment. I suspect the factory originals were in there (corroded as hell and the wires were numbered 1-6). It felt like I had trouble getting 2 of them to catch the threads, and couldn't really get it tight - the plugs would start to get snug, and then just when they were about to be tight enough they would lose grip (I was only using a 3/8" ratchet, and not tightening them like crazy). I thought nothing of it until I drove about 70 mi and a spark plug blew out. Is it possible if they were the original plugs that taking them out destroyed the threads? It was hard to get them out with the ratchet (had to use a long torque wrench, don't make fun of me lol) The threading on the plugs themselves looked ok... I wonder if there is just debris clogging up the threads on the cylinder head. Anyway, I tried putting the new plugs back in and just getting them to that "snug, but about to lose grip" feeling. No success. Started it up and immediately blew out a different plug this time. Also, there was immediately a strong electrical smell... I wonder if the plug shorted against something after it fell out (it was still attached to the wire). Could I have also blown a fuse somewhere? Any help would be appreciated. I would like to go a cheap but reliable route...it seems taking it to my mechanic to get the heads re-threaded could be costly. And hopefully my torque wrench is not out of calibration now, lol.

 

[koda2000]

You will need to install heli-coils (or similar repair theads) in any damaged holes. This involves drilling out the hole and tapping it, screwing in a stainless steel coil and pinning it in place. This repair is very strong (stronger that the original aluminum threads) and makes an excellent repair.

This is what a thread repair kit looks like...

 

[MrQ]

Make sure when you do this to not have the cylinder at top dead center. You go too far and you can hit the piston with the drill bit. After drilling, make sure to vacuum out the cylinder. Last thing you want is to compound the issue by getting metal shavings in the engine.

 

[koda2000]

Make sure when you do this to not have the cylinder at top dead center. You go too far and you can hit the piston with the drill bit. After drilling, make sure to vacuum out the cylinder. Last thing you want is to compound the issue by getting metal shavings in the engine.

Top dead center or bottom of the stroke? If the piston is up you'll almost certainly hit it. Also, put grease on the drill bit and tap to catch most of the metal chips. A few chips will still get into the cylinder, but they won't do any harm.

 

[MrQ]

It should not be at the top of the stroke. I would still vacuum out the spark plug hole after drilling and tapping. Better to be safe than sorry.

 

[koda2000]

It should not be at the top of the stroke. I would still vacuum out the spark plug hole after drilling and tapping. Better to be safe than sorry.

Sorry you did say not.

 

[Gary Crist]

Working on VWs back in 190dirt, we did a lot of those repairs.
Just grease up the bit forget vacuum the minor amount of Al chips
will not hurt a thing.

Next time, use anti-seize on the plugs!
Also the reason they probably stripped was carbon build-up on plug threads.
So back out he plug till it gets hard then STOP!! Run it back in some and spray
carb cleaner or some carbon eater on the plug base. Let it soak. Run them back in
and repeat till it comes out.

BTW Blue East Off oven cleaner is great for carbon eating, especially,
it work great on carbs too. Not the yellow can as it has lye in it.

 

[C420sailor]

Before you worry about the strength of the repair, helicoils are used as the factory method for securing spark plugs into reciprocating aircraft engines.

Grease on the bit is excellent advice, and go slow. I’ve heard of people filling the cylinder with shaving cream, too. The fine chips that aren’t stuck to the greasy bit are caught by the shave cream, and then you can vacuum the cream out.