conor1148

hello, i just swapped my spark plugs and i had no problems except for cylinder 2. I seated it (kinda awkard to get to) and it turned smoothly for a couple turns with a small hose then instead the threading having a sudden stop like the other plugs, it slowly gets harder to turn.

i knew to stop then. i havent seen any damage or metal shavings so how do i know if I've cross threaded or stripped something? the plug also went in only half way (judging from the untouched grease on those threads) but went in smoothly for about 4 or 5 turns so i thought i was good.

thank you for your help

FrostByte

Drop something?

2K6V6PONY

I have the exact same problem. After researching it seems that many 4.0l v6 owners are having this same issues. Not sure what the exact cause is though but its with that exact same cylinder. First thing you want to buy to try to fix it is a 14mm back-tap tool. It goes into the spark plug well and opens up and re-taps the threads from the inside out. The reason for this is when you re-tap it you might get metal shavings into the cylinder head using a normal tap going inwards towards the cylinder. The back-tap pulls any shavings out towards you so you dont get trash into your motor.

If the back-tap doesnt work if the threads are completely gone you will need to get a helicoil kit which will add new threads into the plug well.

Derf00

Back-tap is also known as Thread Chaser. You may have more success finding the tool under that name.

That said the tool will be of no use if you can't get it into the hole at the corret angle (straight). In fact it could make the problem worse since the tool is designed to clean the the threads and fix bent/burnished threads.

You prevent shavings from falling by using some moly grease on the threads of the tool before you insert it.

2K6V6PONY

A thread chaser looks similar but certainly is not the same as a back-tap tool. The back tap tool inserts completely into the spark plug well and then you use a screw on the end to open up the threads once its all of the way inserted and thread backwards working from the inside of the hole outwards. No molly grease needed since no shavings will get into the cylinder head because your working from inside out.

Here is the back-tap tool that I purchased for reference -

flyhigh@mach1

Is there any way to avoid this mess? I can't believe that just taking out the plug messes up the threads in the head! I hear only take out the plugs on a dead cold engine. I plan on changing my plugs at 100,000 miles. Could this have been avoided?

2K6V6PONY

Well based on my bad experience with the issue and the advice of others on this forum here is the best way to avoid potential disaster.

Step 1 - Before removing any spark plug spray a bit of penatrating oil into the spark plug wells to help loosen them up. Let the penatrating oil sit for an hour or so.

Step 2 - With a "COLD" engine carefully remove the plugs. Take it nice and slow.

Step 3 - I recommend you use NGK spark plugs either G-Power or V-Power instead of any other available options. The reason why is all NGK brand plugs have a special plating on them that help prevent corrosion and seizure while in the cylinder head. (Do NOT use an anti-seize compound on the threads. It can trick you into over-tightening the plugs causing you to damage the threads on the plug and in the spark plug well \ cylinder head.

Step 4 - Make sure you gap the plugs to the proper manufacturer spec.

Step 5 - Hand tighten all plugs as much as you can before you take the socket wrench to them. When you have the socket wrench on them and you feel like your running into a spot where its not turning as easily as it should carefully back the plug out 1/4 turn and then re-tighten until its fully installed. Be EXTREMELY careful not to overtighten the plugs this may be where I went wrong its hard to say.

Step 6- Squeeze a small ammount of die-electric grease into each spark plug boot before you pop them back on. Wouldnt be a bad idea to remove the boots from the ignition coil and put some on them as well. Make sure the boots are fully seated onto the plugs and the ignition coil.

Step 7 - Take your mustang for a spin. If everything went well it should drive great and have no issues.

BTW - If anybody ends up in a situation like I did and messes up the threading in the spark plug well \ cylinder head use a 14mm Back-Tap tool to repair. Its a life saver I promise.

I hope this helps. I know there are alot of write-ups on this forum about this but atleast I can give advice to avoid what happened to me.

jimkaray

I always use an antisieze and hand tighten. I guess if you only put your faith in what the torque wrench is telling you you could have this problem. Also, this only applies to plugs with the special plating. If it isn't coated or you check your plugs often the plating will degrade.
NGK pdf on antisieze

How do I install spark plugs correctly?

Torch_Vert

I'm with Jim, antiseize every time, and hand tighten. Never have a problem.

I saw a friend's 4.0 where dry installed NGK's had started to seize, coating or not, I much prefer a quality antiseize and a little judgement during install.

conor1148

Sorry I may have accidentally forgot about the thread.

Turns out the factory spark plug was never installed all the way, so there was just heavy deposits in the threads. Slowly turning the plug in with a bit of wd-40 and removing it every couple turns to clean did the trick. definitely runs better now.