Neon spark plug thread repair help

[jos51700]

Long story short, Mrs. JOS51700 called me this morning from the side of the highway. Turns out the Neon spit out the #2 spark plug. I've always torqued these with a torque wrench; they're 14mmx1.25 gasketed plugs. When I pulled the rest, #3 was loose, and the thread-adapter caps on the center posts were loose (stuck in the boot) on 3 of the 4.

I'm looking at in-car thread repair options and hoping some of our more experienced members can offer some insight. I've found the following kit at O'reilly's. It cuts out ALL of the old threads, and then some.

My issue with it is that it majorly oversizes the hole for the new steel insert. On this head, that spark plug hole is very close to the intake valve seat as it is, and I'm concerned about the intake seats losing their press fit. You can see the diameter change in the shank. Dropping a valve on a good bottom end isn't worth it, and if this is possible/likely, I'd rather pull the head and replace it.

I tested the above thread tap on a junker Neon head I had, and it broke head material away near the intake seats:

My options are:
1. Try to find the wire-coil thread repair, so I'm not removing so much material
2. use a shorter insert and cut new threads only far enough to install it (Note the huge taper on the tap that removes material, though). If I did this, I'd have to turn off some threads of the spark plug so I could get it out again, and then...ugh.
3. Replace the head. I'm not opposed to this but that's expensive, and popping the head on Gen 2 Neons is fuuuuucccchhhh.

Machinists of FABO, tell me, what should I do?

 

[Treblig]

The threaded insert doesn't have to go all the way thru into the combustion chamber. Make the threaded hole and leave 3/16 to 1/4" of material at the bottom of the hole to support the valve seat area. The plug should screw all or most of the way in there. It may not be as efficient as it would normally be but it will work for a long time!! Without more pics of the other side (where the plug seats) I can't offer anything else. A car that runs at 95 percent is better than one that doesn't run at all!! Also....would it be wise to use some Loctite so they don't come loose???

 

[diymirage]

If the stocker plugs are 14x1.25...are there any in the 15.5 range?

That would be my first choice, go up one size in plug thread
(Basically resizing the hole without the need for an insert)

 

[Daves69]

.... Make the threaded hole and leave 3/16 to 1/4" of material at the bottom of the hole to support the valve seat area. The plug should screw all or most of the way in there......

Maybe remove 3/16"-1/4" of the plug thread as well to retain the reach......

 

[Kegan B]

Could you use a time-sert on it? If it's close to timing belt change interval may as well change the head, 2gn isn't that bad to work on minus the engine mount bracket.

 

[pishta]

I like that 3/4 depth cutting and leaving the bottom as is. Would get fresh meat for the plugs and keep the valve seat area untouched. I had an old Mazda that had a perpetually loose plug on the #3, seems the head was cross threaded at one time and the threads were just gone. I took a 90 boot and made a metal bracket off the exhaust bolt and bent the thing so it would press a piece of wood against the 90. It kept the plug in! That engine was so ghetto: I ran a piece of all strut over the thermostat housing using threaded rod off 2 bolt bosses as those stat housing bolt holes were stripped too. I never had an issue with either farm repair. Distributor seized up on me and snapped the shaft. That was all she wrote.

 

[jos51700]

Could you use a time-sert on it? If it's close to timing belt change interval may as well change the head, 2gn isn't that bad to work on minus the engine mount bracket.

Imma disagree, I think 2nd gen are absolute bitches to work on.

That said, you have a DAMN GOOD IDEA. I'm halfway to another timing belt interval, and will secure a head to change at that time!! Good Idea, Sir!!

 

[jos51700]

Update:
Found the wire type helicoil kit as a special order at O'Reilly. $225 later it's in hand, includes 6 of each length m14x1.25 thread repair coils. As hoped, the oversize thread is smaller than the one for the threaded insert, but not by much: only 0.050" in diameter. That was enough to not break into the valve seat area, the threads are cut MUCH cleaner, plus this leaves meat for the thread insert if it doesn't work.

Experimenting shows that if i put grease on the tap and cut three turns and back it out, and then clean and regrease, the chips dropped into the cylinder are at a minimum. 11.5 turns to install the coil, and then check and see how much further so I can be sure its installed to complete depth without hanging the helicoil out into the combustion chamber. If that happens the tang won't break off then you gotta try and pull the whole thing out like a big spring and try again.

The tool isn't deep enough for the Neon long-ish spark plug tubes, because you have to hold the tool and turn the mandrel inside it. I ended up gripping the spark plug tube with vise grips until it crushed enough to grip the installing tool, and then rounded them back out by levering a spark plug socket in them after.

If I hadn't had a sample head to practice on, I'd be pulling my hair (and probably the head) out by now.

Not many neon owners here, but hopefully this will help someone with Google skills in the future. I would upload photos of the new oversize hole but phone won't let me. Trust me, it's very nice.

The root cause of all the trouble? MADE IN F$%KNG CHINA autolite spark plugs!!! Their threads are messed up!!!