Thoughts on how to recover from a slightly cross threaded spark plug threads in head?

beady · Nov 3, 2024

Was installing a DUI distributor, coil, wires, and plugs. Got distributor and coil installed and old plugs out. Started installing new plugs and hit a snag.

454, #8 rearmost passenger side. Felt like it went in ok a few turns and then I started tightening with a ratchet, but it didn’t feel right so I stopped.

First thread of the new plug is a little rolled. Neither new plug nor old plug that came out will go in now past a turn or two, obviously I haven’t tried forcing it.

Pic of the new plug I tried to install attached, you can see the first thread is dicked up. There’s a little anti seize on it is why it looks odd.

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Thoughts/options?

Thanks

Goldie Driver · Nov 3, 2024

My first thought would be a tool like this from a local parts store.

Get the thread cleaned up and rock and roll !

Duralast 14mm and 18mm Thread Chaser

Shop for Duralast 14mm and 18mm Thread Chaser with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

beady · Nov 3, 2024

Goldie Driver said:
My first thought would be a tool like this from a local parts store.

Get the thread cleaned up and rock and roll !

Duralast 14mm and 18mm Thread Chaser

Shop for Duralast 14mm and 18mm Thread Chaser with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

Is that deep enough/has enough clearance to get a socket on that hex and fit into the opening in the head?

I thought I read ppl saying those were too large in some cases.

I did pick up a 14x1.25 tap this evening, might order a single ended thread chaser before I try the tap though.

Truck82 · Nov 3, 2024

Goldie Driver said:
My first thought would be a tool like this from a local parts store.

Get the thread cleaned up and rock and roll !

Duralast 14mm and 18mm Thread Chaser

Shop for Duralast 14mm and 18mm Thread Chaser with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

^^Same^^

I have also installed a TimeSert in my dads truck

beady · Nov 3, 2024

I just ordered a regular, tight clearance thread chaser and also a “back tap” which you insert to the good threads, expand, and back out. At least one person had luck on an iron head.

Back tap

Goldie Driver · Nov 3, 2024

beady said:
Is that deep enough/has enough clearance to get a socket on that hex and fit into the opening in the head?

I thought I read ppl saying those were too large in some cases.

I did pick up a 14x1.25 tap this evening, might order a single ended thread chaser before I try the tap though.

I bought something similar ( if not that one ) for Goldie but never used it. I THINK it will fit just like a plug socket but can't say for sure. Seems like it would be totally worthless if it did not.

Ricko1966 · Nov 3, 2024

beady said:
Is that deep enough/has enough clearance to get a socket on that hex and fit into the opening in the head?

I thought I read ppl saying those were too large in some cases.

I did pick up a 14x1.25 tap this evening, might order a single ended thread chaser before I try the tap though.

Use a chaser. A tap is not first resort. A tap is designed to cut new threads,and it will,and not necessarily at the right angle and not necessarily at the right depth. Meaning you might run the tap mid thread through the remaining threads,which will substantially weaken the threads. Grease the chaser to collect the debris.

ChuckN · Nov 4, 2024

It’s just how my brain works, but my first thought was “of course it had to be #8! It just couldn’t be #1 or 2”.

But, it is what it is. Looking forward to seeing how this comes out- keep us in the loop.

Robert Bare · Nov 4, 2024

You should be able to do it with a rethreader. However, there were made for years, rethreaders that expanded. You push them in, expand it, then back it out. You see, it starts down in the good threads and backs out, cleaning/cutting the threads. I would bet now only old time mechanics and machine shops have them.

tsgs84 · Nov 4, 2024

Goldie Driver said:
My first thought would be a tool like this from a local parts store.

Get the thread cleaned up and rock and roll !

Duralast 14mm and 18mm Thread Chaser

Shop for Duralast 14mm and 18mm Thread Chaser with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.

www.autozone.com

I agree try a thread chaser not a thread tap

Bennyt · Nov 4, 2024

All good advice here.
One additional thing I do is put the engine on exhaust stroke and put an open airline in the exhaust pipe so any trash is blown out.

Grit dog · Nov 5, 2024

Bennyt said:
All good advice here.
One additional thing I do is put the engine on exhaust stroke and put an open airline in the exhaust pipe so any trash is blown out.

That’s a good idea. I’m lazy so I’d clean it up then start the engine with an open hole and let it blow out any debris hopefully.
That said shouldn’t be much debris and small in size as it should only be cleaning up a thread r 2.
And my anecdotal evidence is tore down my old 400sb in high school to do the heads. Unleaded gas finally killed them….
When I did, 2 cyl had large scores in them one of which I’m certain was from a metal Jesus clip off the carb that went straight south one night during a parking lot repair! lol.
Both those cyl had the same compression after I had the heads rebuilt.
Wouldn’t recommend on a new high$ rebuild but wouldn’t sweat it too much on a presumably old motor.
JMO
Good luck!

Ricko1966 · Nov 5, 2024

Grease on the chaser should collect the chips. I do start them with no plug in them though for just a second.

beady · Nov 13, 2024

To follow up, I used the expanding back tap mentioned above and it worked. I wasn’t able to get either a low profile thread chaser or new plug to start though, so I used the back tap several times. I was able to get it to start even fully expanded, so went ahead and really worked on getting a plug started.

I finally succeeded, but it never eased up and went in easily. I think it’s the sheet metal heat shield causing binding on the plug socket/low profile chaser.

In hindsight if I’d tried using a section of rubber hose to try to start the plug I may have avoided the whole situation.

Mike

Strick · Nov 17, 2024

I recently had an issue with #7 on an SBC. As many plugs that I've changed, from TPI Camaro, Vette, Triton Ford, Hemi Dodge, no issues at all with the exception of older Triton blowing plugs out. My ole 76 tho, got me on #7. Made in Mexico Autolite looking just like the previous post. I ran my Heli in behind & screwed the old AC plug back in. Junk parts from foreign places sure mess you up sometimes.

HS

Thoughts on how to recover from a slightly cross threaded spark plug threads in head?

beady

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Goldie Driver

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beady

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Truck82

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beady

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tsgs84

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