98 Expedition - Spark Plug Torque to prevent spitting plugs

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637
Location
Florida
I am changing the plugs on my 98 Expedition 5.4 4x4. Torkspec website says 10 lbs torque on plugs to head, but I have also read to increase torque to prevent spitting plugs. Anyone know the magic number to torque these into the triton aluminum heads? I have spit a plug before and would like to prevent it again if I can. Was there ever a TSB?
 
Messages
637
Location
Florida
Originally Posted by bdcardinal
From the FSM 16-20Nm or 12-14ft-lb
So there was no TSB to prevent spitting plugs out of head?
 
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9,986
Location
Waco, TX
There's only 3 THREADS of aluminum holding each plug in. It's not hard to strip them out. 12-14ft-lb and no more than that.
 
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23,509
Location
MA, Mittelfranken.de
In that range you are getting into lb-in if you need any sort of real accuracy and you do which eliminates most 3/8 tools. If you use never seize the number will be even lower, hand slightly firmer than snug and call it good. In my experience (not that I am a big Ford guy, far from it) they seem to let go more when tightened to the spec after changing them.
 
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10,060
Location
Central Washington
There is a site out there that advises using some rediculous high torque on the plugs but I think thats a bad ida. Ive done a little research and Ive found 20-25ft lbs is doable on 4 thread heads. On the newer 8 thread heads I just go straight to 25ft lbs and dont even think about it. They dont loosen after that. I popped 2 plugs on my 2002 and both times it was because the plugs had loosened until they blew out. Ive done some other mod motor vehicles and often find at least one spark plug loose and coated in the brown-orange soot from the gasses escaping up the threads. imo 10ft lbs is too little torque to prevent loosening and backing out over time. If you want to be really safe torque to factory 10ftlbs and then go back and retorque every 10-20k
 
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Messages
637
Location
Florida
I was also thinking about the anti-seize. It does just what it says, prevents the different metals from seizing, but can't help but wonder if that contributes to plugs loosening and blowing out. Perhaps it is more due to dissimilar metals without anti-seize causing galvanic corrosion on the aluminum heads, weakening the aluminum threads.
 
Messages
23,509
Location
MA, Mittelfranken.de
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
 
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14,457
Location
Santa Barbara, CA
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
I would say that now is the perfect time to repair every cylinder if the OP plans on keeping the vehicle long term.
 
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42,374
Location
Ontario, Canada
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.
 
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6,544
Location
Katy, Republic of Texas
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.
 
Messages
611
Location
US
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.
 
Messages
14,457
Location
Santa Barbara, CA
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.
 
Messages
1,784
Location
Wisconsin
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
 
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