Spark plug thread issue

Dober_paw

Member
Location
MO
51 8N side. Been about 3yrs/100 hours since I pulled plugs and checked the insulator color etc.. 1,2 3 came out easy as expected - but 4 wouldn't move. Careful application of pressure and some liquid wrench oil and it slowly started . . . but needed the wrench all the way till it came out. See pictures for thread damage. Autolite 437s.
I've been pulling/inserting plugs for 60 years so I'm 99.99% sure I didn't insert it cross threaded - I know that they go in by hand and then just tighten up the last half turn.
So - is this just a rust issue ? or what ? How do I clean the head threads - don't want to strong arm the new plug in. A YT search tells me I should be looking for a 14mm x 1.25mm plug tap but I've no experience in this area - what sort of problems am I going to fall into if I don't seek/follow forum advice/help ?
BTW - all 4 showed that combustion was healthy - almost makes me wish I'd left well enough alone - but NGK 3112 are waiting to go in .

mvphoto60636.jpg
 
(quoted from post at 18:21:46 08/23/20) Pack tap with grease, run in and out. Clean seating surface in head.
hat is a good idea. It lubricates and catches what the tap cuts off. Good practice for use with a thread chaser as well.
 

Looking at the gasket on that plug, it looks like it was not tight, which let some carbon build up in the threads. No problem, run a thread chaser on it and be on your way. It does not look like it was cross threaded.
 
Because the spark plugs are recessed in the head, I blow out the recess with
compressed air before removing a plug. If the debris is resistant to the
compressed air, I use a brush to dislodge it, followed by more compressed air.
This helps ensure that the gasket is fully seated when installing the new plug,
as well as preventing the debris from falling into the cylinder when the plug is
removed.
 
(quoted from post at 22:01:25 08/23/20) Because the spark plugs are recessed in the head, I blow out the recess with
compressed air before removing a plug. If the debris is resistant to the
compressed air, I use a brush to dislodge it, followed by more compressed air.
This helps ensure that the gasket is fully seated when installing the new plug,
as well as preventing the debris from falling into the cylinder when the plug is
removed.

Great advice and very good practice!
 
Thank you forum - I was afraid I was deep into trouble - hood, tank, head . . . Will visit NAPA this morning & add a new tool to the toolbox. I've no tapping/chasing experience - do I just grease it and run it in, slowly, once . . . or a little at a time in/out/in/out ? I'm thinking just the once?? Can I run it in one of the OK plugs 1st to get a 'feel' for the operation? Sorry for all the questions.
 
If possible, run the cylinder to TDC compression. Your dist rotor will tell you where that is and the points opening will tell you when the plug fires. Blow air into the hole and get rid of debris. Grease up the thread chaser and work it in slowly. in-out-in-out....
After your done, blow the hole out again. Anti-seize your new plugs. Copper is the high temp stuff.
 

A good reason for TDC is so the valves will be closed and out of the way of the chaser, if it is threaded in too far.
I'm not sure if a long chaser would hit if the valve was open, but better to be safe.
Maybe someone else might know if you could hit and bend a valve this way if a valve was open.
 
Hitting valves occurred to me too - so I marked the tap at the depth of the original plugs so I knew when to stop - BUT - it only took gentle torque in/out to clear the threads, I'd have had to ignore the increased resistance and really force it to damage valves.
Again Thank You forum - all 4 cleaned out and plugs now run in fully w/ just fingers. Mission creep but new skill learnt. Now back to the exhaust manifold. :D
 
FORD TRACTOR OEM Spark Plugs are spec'd at Champion H10, 14mm. Since then, Champion introduced a hotter, better plug, the H12. AUTO-LITE 437 is a perfect equivalent. ALL work just fine, but you can buy whatever you want to spend your $$$ on. Always clean out plug wells with compressed air before pulling spark plugs out. It prevent debris from falling into chambers and onto the threads. Yes plugs are 14mm x 1.25. Best to use a 13/16 6-PT deep well socket and apply slow, gentle, even pressure. If stubborn, spray some PB Blaster or Liquid Wrench on base of plug and let set for a spell. Use a breaker bar only if necessary. 14mm x 1.25 is a standard Metric size, nothing special or fancy, and you can buy a tap at any tooling supply company such as MSC. Many fellas don't realize it is a Metric size and will try 1/2" or 5/8" x 20 taps. 1/2 is too small and 5/8 is too big. There aren't too many Metric parts on Fords. The plugs are as industry standard was such. Also, FWIW & FYI, generator armature shafts were Metric as well and were a special combo size -Metric thread end, INCH TPI. I.E gens had .59" (15mm) x 20 and .69" (17mm)x 20 as well their pulleys and hex nuts.

Tim Daley(MI)
 

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