Recently attempted to replace my plugs and I believe that two of the plug holes are messed up.
(I have very limited rotary knowledge so pardon my crude explanation)

When removing the old ones for replacement, I noticed that the two plugs on the rotor towards the nose of the car were significantly more difficult to remove than the two on the rotor towards the cabin. The one I know is messed up is the Leading one. I haven't tried installing the Trailing plug yet, but I believe it will be messed up as well, as it was just as difficult to remove as that other one on the same "front" rotor. I think that the cause of the messed up holes is the old spark plug bonding with the threads of the hole (maybe due to excess heat? The engine overheated not too long ago) and that may be what messed it up.

I'm honestly not sure of the exact cause or what I should do. Does anyone have any ideas? I don't have the tools to remove the engine from the car. (It's an N/A, if that makes a difference.) Thanks in advance, guys.

 

If the plug refused to go back into the threads, or the threads are gone from it being cross threaded over the years, I would re-tap the threads. Take a tap and cover it in grease... The shavings from the spark plug hole will stick to the grease applied to the tap while cleaning up the threads. Make sure to go slow and clean off the shavings every few turns and apply new grease. It sucks, I know, but there isn't many options.

Option 2: Go get yourself some Helicoil. If your not familiar with Helicoil, do some research on goggle and youtube before you dive in. I must say its not the easiest thing to work with but once its on there its damn strong and worth the hassle. For a spark plug I would be skeptical but like I said there isn't many cheap options.

Good luck! Which ever fix you decide to go with just take your time and you'll be okay

 

While the advice above is excellent, I'll say do not attempt yourself.

It seems you're not at a level high enough to try to fix the threads. If you eff up, you're looking at new housings and a complete tear down.

edit: This doesn't mean you have to take it to a shop. But at least find someone with previous experience dealing with messed up spark plug threads in aluminum (can be on a piston engine). You want a meticulous, experienced hand to do this without rushing.

 

Boy I'd be very curious to see how you'd drill that out with the engine still installed in the car...I'm guessing a 90 degree cordless drill would have to be used. It's aluminum, soft, old metal that's prone to cracking and if you go in crooked - no bueno.

 

If you remove the A.C. compressor and power steering pump and bracket, the spark plugs should be easy enough to get at with a tap. I bought a special spark plug tap from Matco for just such an occasion. Glad I haven't had to use it yet, lol.

What do the threads on the plugs look like that came out of the engine? Sometimes they can be tight coming out and you will see aluminum on the threads. This is of course not good but its workable.

 

Helicoil taps aren't that much bigger than the actual tap for the original thread but will most likely still call for a tap drill. If it were me, I would see if I could get a reamer the size of the helicoil tap drill (MSC has reamers in .001" increments). Reamers follow the hole and can't be forced to "walk" like a drill and don't end cut. You might have to cut a good amount of the shank off but that's not really a big deal. I would also half-*** grind some flats for a small adjustable wrench and try doing it by hand before going to anything powered. Have another set of eyes looking from the front of the car to tell you if you have it angled up or down while you keep square left to right. It will seem iffy at first but will start to guide itself as it machines the threads out. I would also coat it well with grease, remove, clean, and reload with grease often. I've been a machinist for thirty years and have been in many similar situations. Just be very careful and don't rush it.