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Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: bdcardinal] #5131377 06/11/19 12:57 PM
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OVERKILL Offline
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Originally Posted by bdcardinal
Originally Posted by Schmoe
Ford days it's a spark plug problem, not a head problem.


Well I believe that when my poo turns purple and smells like rainbow sherbet.


Indeed.

From a purely engineering standpoint, my understanding of how this was developed, and why it failed is as follows:

- Ford previously had full-thread holes in the heads. This was a PITA to get the plugs to centre when being installed on the assembly line so it was looked at how they could improve the self-seating ability of the plugs in the holes for fast turn-down on the line.

- Research was performed and the results indicated that sufficient engagement was provided by ~3 threads, this meant that the remainder of the hole could be bored smooth so that the plug could be dropped down the hole and tightened down extremely quickly, since the smooth section set the plug straight.

- Research was NOT done to explore the behaviour of this setup once damage to the threads had taken place due to removal/installation; there was no testing as to how this would fare with in-the-field service.

- So from a design standpoint, the 3-threads were technically "sufficient", however, as we all know, the risk of damage to those threads on a subsequent long-interval removal and install is extremely high. It doesn't take much galling to compromise the integrity of this setup and result in a loose plug, which may in turn become a blow-out.


2019 RAM 1500 Sport - Mobil 1 EP 0w-20, FRAM Ultra
2016 Grand Cherokee SRT - Ravenol SSL 0w-40, FRAM Ultra
Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: Fitz98] #5131397 06/11/19 01:21 PM
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Originally Posted by Schmoe
Ford days it's a spark plug problem, not a head problem.

Yup, and that is why in late '02/early '03 they redesigned the heads to have 7-8 threads (and those heads have no issues).

Most forums people have had good luck with Motorcraft plugs installed dry and torqued to ~24 ft lbs.

My '02 has a used '03 motor in it, so it has the newer heads with more thread.


2018 Santa Fe: PP 10W-30/OEM/5k
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Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: Trav] #5131401 06/11/19 01:24 PM
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talest Offline
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Originally Posted by Trav
The problem with these is not anti seize or anything else its the 3 threads that is the root issue that even when new were weak, it is just bad engineering. Now you get to repair their mistakes, course engineers know best right. LOL


Good to know it was not just the Northstar with stupid thread designs. Stupid.

Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: blupupher] #5131618 06/11/19 06:11 PM
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bdcardinal Offline
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Originally Posted by blupupher
Originally Posted by Schmoe
Ford days it's a spark plug problem, not a head problem.

Yup, and that is why in late '02/early '03 they redesigned the heads to have 7-8 threads (and those heads have no issues).

Most forums people have had good luck with Motorcraft plugs installed dry and torqued to ~24 ft lbs.

My '02 has a used '03 motor in it, so it has the newer heads with more thread.


Even the heads with 7-8 threads shoot plugs. However the frequency is a LOT less.


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1995 Ford Mustang GT

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Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: Fitz98] #5132351 06/12/19 02:01 PM
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Black_Thunder Offline
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I torqued mine to 28 ft lbs.




I feel an added issue is they weren't installed tight enough from factory and when they loosen up the compression cycles would beat the plug around against the threads causing them to wear or dislodge and eventually fail

Last edited by Black_Thunder; 06/12/19 02:02 PM.

I'd buy Callahan autoparts if I could.
Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: Fitz98] #5132415 06/12/19 03:09 PM
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red7404 Offline
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i helped a guy with a fuel dragster once. 392, blower ect. stop when the gasket compress.

Re: 98 Expedition - Spark Plug Torque to prevent spitting plugs [Re: Fitz98] #5132448 06/12/19 04:06 PM
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mk378 Offline
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Gasket?

They're taper seat plugs.

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