Testing chased spark plug threads

 
Old 04-14-2019, 11:19 AM
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Default Testing chased spark plug threads

Hey All. I am working on a 2000 Civic EX and when I was removing the spark plugs the other day and 2 were pretty seized. Guess I pushed off spark plug maintenance too long (actually a long dumb story, I am way too behind on taking care of this car). I soaked them in penetrating oil and slowly worked them out (lots of 1/4 turns back and forth). This was hard work and they came out with several threads of aluminum. Cylinder #2 had some head material and cylinder #1 was worse. I got a spark plug tap and chased the threads. I used a 14mm-1.25 4 flute spark plug tap (Irwin/Hanson Spark Plug Tap, p/n 2449) and a #8 tap socket (Lisle 70500 Tap Socket Set) on a ~10" 3/8 socket extension with a thumbwheel ratchet. I now realize I probably should have tried an actual chasing tap first so hopefully it didn't make thing too much worse.

My question is: How do I know or can test if the threads are strong enough to last? Yes, if they jump or strip before getting to a torque spec that is clear but if they hold is that it? Run the engine until warm a few time and if they hold it should be good?? I really don't want to shoot a plug on a drive; as I commute ~50 miles to work and often drive ~40 miles in to the city. Limping the car back that far would be bad. I would really like to test as much as I can close to home first.

I did run the tap in with lots of anti-seize copper grease to capture the cuttings. I also ran a shop vac, with 14" of ~1/2" diameter poly tube taped on the hose, down in to the threads and cylinder to get anything the grease missed. Also double checked for chips with a cheap Android borescope. About to use some Q-tips or toothbrush, held by locking forceps, to further clean things out as well. Then a compression test (one of the things I was wanted to do prior to the spark plug issue), and why I haven't seen if the spark plugs hold at full torque spec yet. But I wanted to ask early on and avoid another dumb move. Also planning an oil change soon after all this to get the penetrating oil and what not that passed by the rings out.

Thanks!!!

Old spark plugs. Sad #1 and #2.
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Old 04-16-2019, 05:13 AM
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Default Re: Testing chased spark plug threads

Send it! There are enough good threads to hold the spark plug in. Get what you can of the aluminum out.

If this were a race motor or forced induction motor, I would say find another head. However, for a stock commuter....You'll be fine.
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Old 05-28-2019, 08:12 AM
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Default Re: Testing chased spark plug threads

Originally Posted by AllMtrRex View Post
Send it! There are enough good threads to hold the spark plug in. Get what you can of the aluminum out.

If this were a race motor or forced induction motor, I would say find another head. However, for a stock commuter....You'll be fine.
what he said.

If you strip the threads you can helicoil or time-sert with time-sert being the best option from my experience.
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Old 05-29-2019, 11:20 AM
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Default Re: Testing chased spark plug threads

Thanks for the replies!

Just to follow up:I did the checks on the engine and found what I needed. Then I installed some new plugs and did an oil change. No problem torquing the plugs. The plugs that went in the 2 holes I chased/tapped went in so smooth it can be done by hand, just an extension with plug socket, no ratchet until the torque wrench. I probably put 200 to 500 miles on the car before doing a bigger service where I remove the plugs again to make things easier (I needed to rotate the crank). After all that I have now probably put another ~200 miles on it. So after running the tap I have torqued the plugs twice and driven <1000 miles and things have been good so far. Fingers crossed!!

Just now I am rereading AllMtrRex comment again about threads I am not sure exactly where on the head you are talking about having "There are enough good threads" but wanted to point out the material on the plug came from the cylinder/spark side not plug cable side of the spark plug. So that head metal, stuck in the threads of the spark plug, passed over all of the threads on the head on the plug's way out, not just a few. So I did probably damage every thread in that hole. But I figure you are thinking it was mostly on the minor diameters (thread tips) and was probably worse closest to where that metal came off the head and as the plug came out that head metal also flattened in to the spark plug some making further damage less, maybe??

Yeah Dibones, initially I was thinking the threads were so trashed (before I even tried the tap, as I had to order it) I got a helicoil setup. One thing I did find annoying is the info out there online is not super clear if you are looking at a coil or insert but having the part in hand it is super clear. This made for some odd interactions on the phone with the parts store vs being there in person. The insert seems the best but I really wanted to avoid pulling the head (a good amount of drilling and probably best on a drill press). It looks like the coil could be installed with the head on but maybe kind of difficult due to the depth of the spark plug tube. Just hoping it doesn't come to that. Thanks guys!
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Old 05-30-2019, 06:17 AM
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Default Re: Testing chased spark plug threads

I should have said tap/chase the plug hole (like you did) first. I thought I had. However, I only speak from experience on any of my comments. I had the same head, same deal, close to the same amount of threads. Years ago, after tap/chase of the plug hole. I spent very little time on this. It was a send it deal and that's exactly what I did and it ran fine for years until I sold it off.
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Old 06-09-2019, 09:01 PM
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Default Re: Testing chased spark plug threads

Oh cool, got ya. Great that makes me feel better. So far so good and lessons learned. Thanks!!
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