I cross threaded a spark plug. How screwed am I?

[atericel]

I was doing spark plugs and valve check today, and the bottom plug on the left side went in a bit wonky. I didn't realize it until until I was getting things buttoned up, and the cover that goes over the coils wasn't going on right, due to the plug sticking out too far. Anyway, the plug looks fine, but shining a light up into the hole, I can see the thread are a little bit boogered up.

 

My thinking is I should just try to tap it out, but so far I haven't found the right thread size, and I think I'll have to go buy the right size tap. Am I just looking for M14x1.25, which seems to be standard? Or is this a horrible idea? Is there some other tool I should be looking for?

 

Edit- looks like I'd looking for a M10x1.0 tap. Seems like this would involve removing the head to be sure there's no shavings in the cylinder.

[Skywagon]

I wouldn't use a tap as my first remedy.  I would look for and buy a thread chaser of same size.  Unless it is completely destroyed, usually a thread chaser will get your threads cleaned up.

 

Wait for DR, Brad, and a couple of others to weigh in who have far better machine skills than me, but I have used thread chasers on spark plug hole and a number of things successully.  They look like this and allow you to stick it in far enough to catch some good threads before redoing the bad ones.  They are tapered .

 

[The Fabricator]

Try to figure out how far in the spark plug is.  It may not be full depth.  Compare the sunken height with the other side's spark plug. Count the turns to remove the spark plug.

Thread chaser or tap.  Apply grease to the tap so chips stick to it.  Thread in a few turns, remove tap, clean chips off, repeat.  

Also, remove the throttle body, position the engine so the inlet valve is open a bit,  position an air hose so it blows into the port and forces air out the spark plug hole to blow chips out as they are created.  You could probably also use a vacuum cleaner exhaust.  A fully opened valve may be visible in the spark plug hole and so the tap may hit it if you thread it in far enough, if there is an interference. Count the turns.

You may not need to go full depth any way.  Try the spark plug when the tap reaches 1/2 depth, or 2/3, etc. Usually is best to go full depth with the tap because some chips may be pushed ahead of the tap and may stick in the thread groove and not get blown out by the compressed air.

 

[atericel]

Skywagon and The Fabricator, thanks for your suggestions. I have a thread chaser on the way from Amazon, and will be trying that first. I'm not sure I am comfortable removing the throttle body, and I'm definitely not comfortable removing the cylinder head. A similar old thread on another forum (that I can no longer find) suggested doing this with all valves closed ( i.e. at TDC), and blowing air through the top spark plug hole to blow any chips out the bottom, which makes some sense to me. I think I may also try to get one of those cheap borescope cameras off Amazon, and see if I can see any chips in the cylinder after running the thread chaser in there.

 

And now after typing all that out, I have myself wondering if I shouldn't just tow it to a shop, and have them remove the head to fix this properly.

[dirtrider]

1 hour ago, atericel said:

Skywagon and The Fabricator, thanks for your suggestions. I have a thread chaser on the way from Amazon, and will be trying that first. I'm not sure I am comfortable removing the throttle body, and I'm definitely not comfortable removing the cylinder head. A similar old thread on another forum (that I can no longer find) suggested doing this with all valves closed ( i.e. at TDC), and blowing air through the top spark plug hole to blow any chips out the bottom, which makes some sense to me. I think I may also try to get one of those cheap borescope cameras off Amazon, and see if I can see any chips in the cylinder after running the thread chaser in there.

 

And now after typing all that out, I have myself wondering if I shouldn't just tow it to a shop, and have them remove the head to fix this properly.

Afternoon atericel

 

Typically I wouldn't use grease on the thread chaser, a little WD-40 works just fine for alloy thread chasing. 

 

On the chips, probably shouldn't be a lot as you are not making new threads so hopefully you are just straightening out the existing threads.  Any chips usually means the you are removing material that shouldn't be removed. But some are probably going to happen if it was cross-threaded deeply.

 

In any case, on similar situations I usually remove the upper spark plug then blow compressed air in the upper plug hole as that will blow the chips out through the lower spark plug hole.

 

It helps to have that side piston close (but not exactly at) at top dead center compression (both valves closed) so when compressed air is blown in it HAS TO exit the lower spark plug hole. You don't want the piston at exactly TDC as that increases the risk of the thread chaser hitting the piston top  (but on the lower plug the lower plug is along ways from the piston top)

 

If you don't have an air compressor then a can of "air duster" or something similar should work   (if using something like a can of compressed air then use a rag or something to seal the nozzle tube to the upper spark plug hole so you don't lose a lot of air pressure back out that hole)

[atericel]

Thanks, DR. I like the WD-40 suggestion, as I was a little worried about getting grease and chips in the cylider. I have an air compressor, so I should hopefully be able to blast any debris out.

[dirtrider]

Just now, atericel said:

Thanks, DR. I like the WD-40 suggestion, as I was a litle worried about getting grease and chips in the cylider. I have an air compressor, so I should hopefully be able to blast any debris out.

Afternoon atericel

 

Yes, that I why I don't like grease is situations like this, if you manage to push some chips into the chamber they will be very difficult to dislodge & blow out. 

 

Just make sure the valves are closed so you don't blow anything out into the throttle body or between the exhaust valve & valve seat.