Cross Threading?


#1

I managed to replace the #3, 5, 4 and 6 spark plugs in my 1992 Buick Century (V6) but still, could not remove the #2 boot (as explained in my previous post). Also, I could not remove the #1 plug. As I tried to turn the ratchet wrench (counter-clockwise of course) it seemed to get harder to turn. Could it have gotten cross-threaded from the previous installation? The engine was still a little warm, about 1.5 hours from running. Should I have waited for complete cool down? Can a spray lubricant be used to loosen it?


#2

Yes @jmcarc, use a penetrating oil to help loosen that plug. Spray Liquid Wrench or similar around the base of the plug and leave it to penetrate for a while and then work the wrench back and forth to get the threads to work free.

If the plug was improperly installed, i.e. cross threaded, it would have been a struggle to get it tightened. If you installed it and crossed the threads you would have known there was a problem.


#3

Are these platinum plugs, installed for more than 60, 000 miles? There’s crud that can build-up on the threads and make removal difficult. I prefer to work it out slowly by screwing it back in a quarter turn when it begins to bind up, then back out until it binds again, and repeat until it is removed.


#4

“Spray Liquid Wrench or similar …”

This is the “similar” ➔


#5

BustedKnuckles: They’re copper plugs with 54k miles on them.


#6

Personally I would try a little harder to remove the plug, perhaps working it back and forth rapidly. It’s pretty hard to strip out a spark plug hole in a cast iron head. If you had cross threaded it in last time you would have felt it.

How old are these plug wires? If they’re that hard to remove why not just replace them?


#7

In some engines the last thread or so of the plug protrudes past the threads of the hole and carbon buildup on that last thread can make the plug seem to tighten as you initially try to remove it. I don’t have access to documents to know if this engine is one of those, but your symptoms fit.

I think a combination of penetrating lubricant and Ase’s suggestion of working it back and forth is the best way to approach this.

Good luck.


#8

As others have said, if it won’t turn out, stop, spray it with penetrating oil, then turn it back in. Work it in and out and it will loosen up a little more on each in/out cycle…


#9

It might not be ‘cross threaded’. What can happen is that the aluminum of the head becomes fused (think welded) to the threads of the spark plug. As you try to drag this metal past the following threads those get distorted increasing the removal effort. About the only thing you can do is to stop when the plug is getting stiff coming out; use penetrating oil; and work the plug in and out until you can finally get it out. I have opined that the reason that it is recommended that the engine be stone cold before the plugs are removed is to forestall this happening. With only 54k on the plug, you might tighten #! back up and let it run until you get a P0301 or P0300 DTC code and then bite the bullet and tear it out of the head.

I was thinking that dealing with dissimilar metal fasteners was a pain but I recollect dealing with simialr steel on steel or steel on cast iron fasteners when rusting is involved can be just as fustrating.

Even if you do get the plug out you probably will have to do a retap and insert or helicoil thread replacement.