Spark Plug Hole Thread Chaser Question

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ARCHINSTL
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Spark Plug Hole Thread Chaser Question

Post by ARCHINSTL » Thu Feb 02, 2012 1:09 pm

The recent Rock Auto monthly link about spark plugs got me to thinking about rethreading a plug hole.
Goldie's #1 plug has always had a very tentative and delicate insertion procedure, unlike the other three holes. I noticed this the first time I replaced the plugs (three times now).
This was a (supposedly) reman head installed by the PO's shop in TN when the OE cracked - about 1K before I bought her.

Sears has a Craftsman rethreading tool for only $7 (cheaper than I would have thought), a Lisle for $6, AutoZone has two similar ones for $7-9, and Snap-on has a very interesting internal-expanding variation for some no-doubt impressive bucks (splatterdog ?).

OT a bit, but - I've always used anti-seize on threads and a torque wrench, realizing that there are two definite schools of thought on lubing threads.
Again OT, but while looking for a price on the Snap-on internal tool, I found this blog, which details info for used S-o searchers: http://snap-on-tool-hunter.blogspot.com/ It details its tools by alphabetical groupings.

Who has experience with chasing plug holes? While successful thus far, I'd like to be prepared next time - I plan on doing the timing belt this year.
Tom M.
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splatterdog
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Re: Spark Plug Hole Thread Chaser Question

Post by splatterdog » Thu Feb 02, 2012 4:14 pm

What ever you do be VERY careful. Depending on where the threads are buggered up would determine the tool. If it's at the top, which it sounds like,the snap on one would be the ticket. Tapped from top or bottom, make sure all the chips are removed from the cylinder. Greasing the tap will hold on to most of them.

I've been pretty fortunate. Out of thousands of plug replacements, I've only had a handful of damaged plug holes. The worst ones required an oversize hole and insert.

I'm always a little nervous about tapping/chasing plug holes. The more metal removed=less to hold the plug. At least the 3a has a good amount of threads. I also would avoid antiseize. It affects torque and can,under the right conditions create resistance. I apply a very small amount only on corroded/sticky holes, usually caused by overdue/crappy plugs. Otherwise most new plugs are nickel plated and need little to no corrosion protection. I do my T4's once a year so they never get a chance to get nasty.

Don't forget to blow gun the plug pocket before removal! I give gasketed plugs a second blast after a few turns as those tend to trap dirt. I pull a fair amount of plugs with gritty threads from the previous tune up. Not very good for the cylinder either.

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Re: Spark Plug Hole Thread Chaser Question

Post by Petros » Thu Feb 02, 2012 5:43 pm

I suspect, as Splat pointed out, if it is badly boogered up retreading them only takes more metal out. If the first few threads get messed up a stiff brush and solvent usually clears any loose metal. And I agree with Splats procedure for removing plugs, spray first, loosen some, spray again. If you do not have compressed air than spray solvent works, and blow with your breath as hard as you can manage.

I have never had a problem with threads on the spark plugs on any of my engines. It always amazes me how many people mess up their spark plug threads. I guess it does not occur to many do-it-your-selfers (and many "speedy tune" type mechanics) that they are threading into soft aluminum, so it must be done by hand, and to visually align it as much as possible while gently turning the socket with your hand (NOT THE RATCHET HANDLE!).

I always use a small amount of anti-seize (on the threads only), it helps prevent getting a plug stuck, prevents corrosion (which I have seen on spark plugs) and make it easier to thread in without cross threading. The metallic anti-seize will not prevent the plug from grounding, and it grounds through the seat or metal washer anyway.

The spark plug taps are not a bad idea to clear any damaged threads at the top of the thread bore, if you chase the holes right when the damage occurs, before the spark plug is forced all the way in. It is worth a try I suppose, but often when you get a car with a messed up spark plug hole, some one had forced it all the way in all cross threaded. Not likely chasing the threads will help much. Those need an insert (drill oversized, thread it, install insert with high temp loc-Tite), much more costly but a more reliable way to fix the problem.

You can make your own thread cleaning tool: take and old spark plug and with a small triangle file cut across the threads, to form a V notch across them in several places around the circumference of the spark plug threads. Clean off all the burrs from the threads (a magnifying glass helps). And than carefully thread it in the spark plug hole with lots of solvent or light oil. Use a small bottle brush with solvent (put it in and thread it out), several times, and that should clear any burs or minor messed up threads. I have not done that on spark plugs, but I have done it on difficult to reach places I could not get a tap into; worked good enough with a short bolt.
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ARCHINSTL
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Re: Spark Plug Hole Thread Chaser Question

Post by ARCHINSTL » Fri Feb 03, 2012 12:43 am

Thanks for the advice from both of you!
I may pop for the Craftsman model if my local friendly (true!) shop does not have a Snap-on I can borrow. Either way, if I do the procedure, I will document it for us.
As mentioned, thus far I have been lucky but still dread the #1 hole.

OT, but in doing a Google Search for info, I discovered several peeps swearing by filling up the cylinder with a) shaving cream or b) foaming soap to catch any errant chips/burrs! The mix is then sucked out by a plastic tube attached to a vac. I would have thought the shaving cream would have sorta evaporated, just as it does on your face if duty calls before applying the razor.
Tom M.
T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"
"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain

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Petros
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Re: Spark Plug Hole Thread Chaser Question

Post by Petros » Fri Feb 03, 2012 12:11 pm

metal particles in the combustion chamber always seem to scare everyone. But frankly I doubt a small amount of tiny particles of soft aluminum will cause any harm. Look at the chucks of hard carbon you break loose with Seafoam or Gumout, I have also seen pieces of spark plugs or exhaust valves break off and the car did not usually suffer damage, it just goes out the exhaust pipe. The aluminum likely burns up with the fuel mixture on the first start.

Not that I would make a habit of it, I just would not worry about it. You likely already got aluminum particles into the chamber when the threads first got boogered up, long gone now and no apparent harm done.
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Re: Spark Plug Hole Thread Chaser Question

Post by marlinh » Wed Apr 18, 2012 11:14 am

When chasing a spark plug hole it is a good idea to put grease in the grooves of the chaser before use. It catches the metal particles preventing them from falling into the combustion chamber. If it's really bad you can thread the chaser in partially remove it and clean the grooves and reapply the grease. Good luck.

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