Why on earth does Ford have specs for spark plug torque on their 4.6? On these engines it's not really the length that's the issue, it's the angle of attack. I'm sure we are all aware that torque is a measure of how much a force acting on an object causes that object to rotate, or a force that tends to rotate or turn things, depending on your perspective. Some folks may also be aware that, since torque equals force multiplied by distance, the length of an extension will alter the actual torque applied to a spark plug in relation to what a torque wrench reads the torque to be but is negligible at the lengths and diameters of the extensions used for replacing the sparkplugs in these engines in a F150 and it's pretty easy to calculate anyway, for practical purposes and not in a lab. We can discount the negligle twist occuring in an extension.
T = F x D
T = torque (in lb-ft)
F = force (in lb)
D = distance (in ft)

Using a ball angle socket so the torque applied around the circumference of applied pressure would be relatively equal the average torque would be relatively easy to calculate if you are mathematically inclined.

However, that does not apply to the normal double universal joint type of flexible adapter that most people have in their tool arsenal. In theory if one could stay within a forty five degree angle the above calculation may work but on this engine there are spark plugs where that is not possible, the angle will be more acute and the standard universal joint flexible adapter will "hang" a bit and that would not transmit the correct torque to the sparkplug and could cause the sparkplug to be under or over torqued.

So, the recommended torque, I'll use 13 lbs ft, shown on a torque wrench will only be accurate at a 0 angle. Disregard the loss from lenght, but toss in the angle of the flexible adapter, the fact that it does not transmit torque at an equl rate depending on the angles of it's pivot assemblies and the loss realized from the clearances between a socket, the flexible adapter, an extension, (or more than one) and a torque wrench and the torque shown on the wrench could be off by 50% or more.

So, yeah, the ideal torque for sparkplugs on a 4.6 may well be 13 lbs ft it's impossible for more than a couple of those sparkplugs to actually get an accurate reading, the rest is best guess.

No wonder so many people have sparkplug blow outs.

This is not a bash on Ford and this engine in particular, since nearly every manufacturer has the same kind of problem with specifying a particular torque rating on an object when that torque rating was predicated on that particular object being torqued was in a laboratory or theoretical situation and not in a real life application.



On another note, torque isn't the best way to accomplish checking tightness anyway, but that's a subject for another discussion.

 

No, the ideal torque is 28 ft/lb, not what the factory says. You are risking loosening and blowout if you follow the factory specs.

http://blownoutsparkplug.com/

FAQ's #51 and #52.

 

Yea, mathematically inclined or not, you still have to know what your shooting for. Your way off man,- and that's WHY they blow out.

 

That was deep,daklander. Would probably confuse most of the younger ones here :o

 

I would be curious to see how much the actual numbers are skewed by the use of a U joint and an extension. Care to calculate?

 

There is a chart somewhere. I've seen it but can't seem to find it now. Single piece extensions didn't throw it off by much, it was like +.10% or something. I'll try and find it.

 

No, the extensions won't throw the measurement off by much and at the low torque required for spark plugs would be negligible. Heads, main bearing caps and other areas where torques are much higher is where that length may cause a significant enough of a misreading to cause a problem and you don't want to use any extensions if at all possible.
The universal joints, on the other hand, could cause a huge problem.

 

The universal joint calculation is shown above, albeit not for the dual pivot type of universal joint adapter.

 

Thanks. I don't know about deep but sometimes things like that get to me, especially after spending over an hour replacing four spark plugs that were relatively easy to get to, compared to the left bank, so the ramblings just kind of flowed.
(I was however, taking my time, using hand tools, blowing away any debris & etc, and sipping a nice libation.)

 

Steel VS Aluminum threads?
More threads are pulled or galled by over torquing with that metal combination than anything else, even electrolysis.
I'll take the factory specs thanks, and I'll use an anti-seize compound.
Here's what I use:


Let me add, the 28 lbs foot listed in your poste FAQs is a dry installatin torque and would, more than likely, correspond to the Ford spec'd torque rating using an anti seize in the actual pull applied to the threads with pull being a more accurate means of measuring fastener tightness.
Also, there is conflicting opinion on use of nickel plated fasteners/spark plugs and electrolysis. In theory, every dissimaler metal assembly will have an occurance of electrolysis of some amount or another. The closer the similarities of the fasteners the less electrolysis.

 

You have it *** backwards. You'll find out the hard way, have fun with that.

 

Just what do I have *** backwards????

 

Make sure to update your thread.

 

That does not explain why I have it *** backwards.

 

I'm not going to, I want you to learn the hard way, since your assuming what Ford does, lol. You have know idea and your posts reflect that. You just think you do, yea, THAT'S "*** backwards". So since you already know so much more than all of us, - learn it for yourself.

Yea, we just spend are time giving false information and need to get back to it, so, buzz off.