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Cross threaded spark plug

I have a 1994 Chevy Beretta and the previous owner put in a spark plug and when they did so, they cross-threaded it. I can get the spark plug out, but how do I fix the ripped out threads on the head?

Go to a local auto store and purchase a Helicoil spark plug thread repair kit.

Apply grease to the flutes of the drill bit provided with the kit and drill out the spark plug hole. Apply grease to the flutes of the tap that comes with the kit and thread the hole. Install the Helicoil thread repair insert.


If I tap the spark plug hole while its on the block, wont I get some metal in the engine?

Use a hose just smaller than the spark-plug hole and vacuum it out.

The grease on the flutes of the drill bit and tap captures the metal chips preventing them from entering the engine.


It doesn’t hurt to be a little paranoid about it too.

About how long does it take to do this?

Do what? Drive to the parts store or install the helicoil?

To install the helicoil

I’ve repaired spark plug threads in less than 20 minutes using the kit.

Also check out the Sav-A-Thread repair kit. This doesn’t require drilling and I believe it’s cheaper than the regular Helicoil repair kit.


Thank you for your help

Wouldn’t it be easier to pull the head off the block, repair the spark plug hole, and then put the head back on? Then there wouldnt be a chance of metal entering the cylinder. If using Sav-A-Thread, what are the chances that a metal shaving may enter the cylinder?

A few aluminum shavings are harmless. Very few will drop in past the greased tools…

SOMETIMES you can simply run a thread chaser in and out a few times to restore the existing threads. It depends on how bad they were damaged…Then you put in a double platinum plug and never touch it again…

Pulling the head is time consuming and expensive. Even if you do the work yourself, you will have a good $200-300 into the job for things like gaskets, coolant, new head bolts (they are not reusable), and other incidentals. Pulling the head should be a last resort, like if it’s on the back bank if it’s a V6 and you’ve tried really hard to find a way to do it, but it’s not going to happen. If all other methods prove to be impossible, then you pull the head, unless you simply have time and money to burn and want an excuse to have a learning project…

So the most cost and time effective way is too use the Sav-A-Thread repair kit? Im worried that metal shavings will enter the cylinder and if that happens, I could be out a motor, which is more than 200 to 300.

Determine the correct thread size. Ask the counterman at the parts store to show you a thread chaser of the correct size. Try that first. Grease the thread chaser in the same way you would a drill or tap…It is VERY important to START the thread chaser in correctly so it restores rather than destroys the threads…

wont the thread chaser drop some metal shaving into the cylinder?

When you run the tap in make sure the piston is in a “down low” position as you dont want to have the piston prevent the tap from doing its job (or damage the piston top).

A real odd ball situation came up one time with a spark plug thread repain in a a 914. The customer came in and told us the threads were damaged (in fact he brought the engine only) and instructed us to tap the spark plug hole and install an insert. The bosses Dad got the job and he was working at it for a long time before he finally got the tap to finally bite and cut some new threads,we thought things would be fine now,well this was very wrong thinking. It turned out that the spark plug hole already had an insert in it (hence the difficulty with the tap) and what had happened was the tap finally cut the top ring of the insert off and screwed the rest of the insert down into the engine,the head had to come off to get the piece of the insert out and no one in the shop was happy that day.

As mentioned MANY TIMES, adding grease in the flutes of the thread chaser will trap the metal shavings. The only other option is to pull the head. Your choice. Grease in the tap, repair can be made in 15 minutes and cost $20. Pull the head, couple hundred bucks just for parts and a good weekend or more.

Caddyman’s suggestion to try cleaning up the threads with a chaser seems to be the best alternative to begin with. Those inserts seem to be tough for the DIYer.