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Originally posted by Russ59:
Anyone have a guess whether the head is cast iron or aluminum?

The independent shop was more confident with the repair if it was a cast iron head. I believe the valve cover is cast aluminum, just not sure about the head itself. The repair manual doesn't mention and I'm on the road for work and can't put my eyes on the car.

According to this site, alum block & head
https://tuningpro.co/honda-k20-vs-k24-engine-guide/

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All engines in the K20 family have aluminum head and block construction and have forged steel crankshafts.

Like I said had it done on the 5.4 which is notorious for this issue, so far it's held up for several years. I would have a go at the one cylinder and see how it holds up over time, it's a well known solution

I would at least try a thread chaser first, you might get lucky. If not, I would try a heli coil kit yourself first.

Update - the thread chaser did not do the trick. It bit and started to grab, however it wouldn't accept a new spark plug.

Next step - create new threads. The OEM Tools kit 25647 would do the trick, however the tapping tool isn't long enough to get a solid tap on the top to seat the new thread insert. Also the drill tap requires a 3/4" socket in order to turn the tap. However, my coil tube is too narrow.

So I've got to seek out a drill tap set up for narrow access. So far, Lisle 65200 seems to be the right setup.Lisle 65200

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Also the drill tap requires a 3/4" socket in order to turn the tap. However, my coil tube is too narrow.

Considering that the majority of engines these days have the spark plug at the bottom of a 4-6-inch-deep hole, that is a poor design.

Whatever you wind up using, be sure the piston is not at the top of its travel when the drill/tap comes through, or you may, at the very least, gouge the top of the piston. Put something like a wooden dowel into the hole as an indicator and turn the crankshaft so it visibly goes down.

At least your plug hole is accessible and not something like #4 cylinder of a Ford Triton.

UPDATE - I tried the thread chaser to no avail. While the thread chaser felt like it was doing it's job, I couldn't get a new spark plug to grab the threads. Moved onto the thread insert method. However, I had to wait for the proper tool (Lisle 65200) which allowed for a longer reach. Boring out the old threads was straightforward (using bearing grease to capture much of the shavings). When I used compressed air to blow out the shavings (bottom dead center on the stroke), the rubber tip on the air nozzle shot off and into the piston chamber!!!!! After two hours of using a flexible claw grabber and a bore scope, I was able to grab the rubber tip and continue with the thread insert. I used a bit of Loctite 271 on the insert per instructions. Waited a few minutes and then seated the insert using the tamping tool. I checked the insert using the bore scope again and it looked good. Finished with a new plug and coil for all four cylinders - no codes or misfires. So, looks like it worked out. It wasn't too complicated and I didn't feel nervous or unsure about cutting the new threads. Easy peasy.

Glad you got it resolved. Guess that JDM K20 will have to wait.

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Originally posted by P250UA5:
Glad you got it resolved. Guess that JDM K20 will have to wait.

Once that rubber tip ended up downhole, I began to run the number on a JDM and the time and parts necessary for the swap. I'm glad I was able to snag the rubber tip with a $4 Harbor Freight tool! If I could figure out how to upload photos, I'd add some of the rubber tip laughing at me from the bottom of the piston chamber.

Yeah, that's a heartwrenching moment.
A bit like dropping the ubiquitous 10mm socket into the nether of the engine bay.
Had a few of those over the weekend myself, working on the Midget. A few handy magnets go along way to recovery.

I wouldn't be a real shade tree job without something like the rubber tip going into the cylinder LOL

Glad it worked out for you!

Good job! Glad you got it done.

The lost rubber tip...