fastbackford351

Well, I guess it was bound to happen sooner or later. I jumped into my trusty, bone stock 2002 GT and fired it up only to be greeted with the PHEW PHEW PHEW PHEW of the #2 sparkplug being blown out of its hole. It took the coil pack with it and cracked it all to pieces.

The threads are whipped and it needs to be helicoiled I suppose but I have some questions about this as this is my first time dealing with this situation.

#1. Why are these heads prone to this and is there anything that can be done to lessen the likelyhood of this happening in the future?

#2. Now that one of them has blown are the others likely to follow?

#3. Any 'gotchas' to look out for when we're doing the repair.


Thank you in advance for your council.

BornToFord

Aluminum heads can have this problem if the plugs are overtightened, or if they are too loose. Ford recommends about 14ft lbs of torque at maximum when installing them.

I had a blown plug on a Fiat 850 Coupe with an aluminum head back in the early 70's, so this is nothing new.

If your plugs were properly installed this most likely would not have happened. I would loosen each remaining plug and re-torque them to be sure they are correct. Unless you have more damaged threads you should be OK.

I spoke to the mechanic at my dealer last week and asked what torque he recommended for installation. He said he never uses a torque wrench and has never had a problem. He just has a good feel for how tight plugs should be. He said he has a kit that can be installed without tearing the engine down, and described an aluminum "Keensert" or similar threaded insert.

Here is an engine builders bulletin I found that describes the problem: http://www.jasperengines.com/pdf/4.6...ed_Threads.pdf

Here is what a locking insert looks like: http://www.newmantools.com/kee.htm

Possibly someone that has done it will advise you on installing an insert in your head.

Mike T

Some of these sparkplugs came from the factory with not enough threads for them in the head. Early 2000's Ford's with the coil packs on the plugs come to mind. They tried to rectify this later with more threads but this is little consolation for some of you guys.

cliffyk

Ford machined the plug bores with just 5 or 6 threads to minimise the possibility of the plugs seizing in the bores over the 100k miles they would be in their per standard service recommendations. There was nothing wrong with this until the engines wound up in the hands of the "I don't need no stinkin' torque wrench" crowd--fellows like BornToFord's mechanic at the "dealership" (I wonder if he knows he could be fired for that?).

The plugs need to be torqued when they are installed, that's what Ford says in the shop manual and they didn't write that down just to be picky. The manual says 11 to 13, lb-ft for dry plugs--I use 14.5 lb-ft because I use never-seize on the plug threads, and use a torque-limiting plug socket which makes it easy:



Harbor freight sells a 1/4" drive torque wrench that is perfect for installing spark plugs on our cars, it is often on sale for $15 or less. If you cannot get a torque wrench or limiting socket then make the plug hand tight and then make it 1/16th turn tighter.

I changed the plugs on my '03 GT literally 10 to 12 times a couple years ago while doing field tests for an aftermarket coil and plug vendor--that's when I got the torque-limiting socket. If has been 35k miles since then and the plugs are all sitting happily right where they belong...

JC316

I am guilty of this. I never use a torque wrench on spark plugs. Never had a plug pop out on me though.

DRAGUL

I don't use a torque wrench either, but after reading this I think I will go and make sure mine are torqued to the right specs.

RMK01GT

I kinda scratching my head at this one, shouldent the torque value be less for lubricated bolts...?

SVTeeshirt

cliffy iirc it is 4 threads, then they upgraded to 8 in later models.

GL, i did it sucessfully, and its harder in a 4valve lol.

cliffyk

With tapered seat plugs the fresh never-seize might allow then to back out until it burns off--the initial lubricant properties are bad in this case, it's the long-term corrosion resistance that's the good part.

If it were a threaded fastener, loaded in tension to secure a joint t'would be as you say, the lube would lessen the required tightening torque.

cliffyk

Some people are sufficiently experienced and lucky--however for the very short bit of time it takes, and that this is a known issue on these engines, why not?

If I caught the FAA mechanic that certifies my engine not torquing the plugs (or anything else) I'd throw him into a spinning prop...