"Plug" story (or not)
Senior User
Joined: Apr 2008
Posts: 365
Likes: 4
From: Round Rock, TX
I just finished looking at this TSB. It appears this spark plug issue only applies to 3V motors? I have an 04 6.8L do I have anything to worry about in terms of breaking plugs or am I in the clear?
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
You are in the clear. Just don't put them in too tight.
Post Fiend
Joined: Mar 2009
Posts: 11,798
Likes: 14
From: Mt. Shasta California
EXv10,
I think your missing the point. With the plug in the head and the engine at full operating temperature the tolerance between the plug and head is at it's tightest thus making the already bad plug design (in a bad head design) more likely to have problems on removal.
This is why Ford specifically states not to remove the plugs from a hot engine.
Here is the TSB. See the first "Caution" note on the first page. This is the same procedure Ford follows on removal.
http://www.wfservices.biz/TSB%20Ford...%20removal.pdf
I think your missing the point. With the plug in the head and the engine at full operating temperature the tolerance between the plug and head is at it's tightest thus making the already bad plug design (in a bad head design) more likely to have problems on removal.
This is why Ford specifically states not to remove the plugs from a hot engine.
Here is the TSB. See the first "Caution" note on the first page. This is the same procedure Ford follows on removal.
http://www.wfservices.biz/TSB%20Ford...%20removal.pdf
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 423
From: Long Island USA
Coefficient of expansion in (10-6 in/in/degrees F) (that's 10 to the minus-6 in/in/degrees F)
Aluminum: 12.3
Steel: 7.3
This means that a steel fastener surrounded by aluminum will not expand as fast as the aluminum. Also, even if the materials were the same, say steel and steel, a fastener will not expand as much as the hole it's in.
That doesn't mean I'm condoning removing plugs on a warm engine.
Conversely, the threads in the warm head (aluminum) expand more than the steel plug, so when you're trying to remove the plug, you may damage the threads because the threads are pulling the tip of the plug that's dirty, and the threads are somewhat larger than the plug is. The tighter the threads, the less likely you will strip them trying to get the plug out. But then, you risk leaving the tip in there.
An earlier version of that TSB (or another one) said to do it on a warm engine. I guess too many techs were stripping the threads so they figured they'd just do it cold and the tip would separate instead.
Aluminum: 12.3
Steel: 7.3
This means that a steel fastener surrounded by aluminum will not expand as fast as the aluminum. Also, even if the materials were the same, say steel and steel, a fastener will not expand as much as the hole it's in.
That doesn't mean I'm condoning removing plugs on a warm engine.
Conversely, the threads in the warm head (aluminum) expand more than the steel plug, so when you're trying to remove the plug, you may damage the threads because the threads are pulling the tip of the plug that's dirty, and the threads are somewhat larger than the plug is. The tighter the threads, the less likely you will strip them trying to get the plug out. But then, you risk leaving the tip in there.
An earlier version of that TSB (or another one) said to do it on a warm engine. I guess too many techs were stripping the threads so they figured they'd just do it cold and the tip would separate instead.
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Mcdanbee
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