icerunner

Guys,
I'm pretty good with a wrench and I dont trust my older snap on torque wrench... I think the excessive "anti-sieze" that I used on the plug threads was the cause .."Less is more" when it comes to "Anti-Sieze". Also, the crush washers on the Denso spark plugs are very tough and it takes a decent amount of torque to crush these "Crush washers" ...again a careful 1/4 to 1/2 turn.

mt_goat

1/2 turn from what point? An extra 1/2 turn from max torque could be enough to completely strip those aluminum threads in the head.

icerunner

After I feel some "tightness" I go another 1/4 to 1/2 turn and I do go by feel. And havent stripped anything in 10 years...under torqued maybe.

On the Denso's, the crush washer is NOT weak or thin I'd say it is at least 1 millimeter on the Densos..after the crush washer has made good contact and started to bite, another 1/4 to 1/2 a turn seems to work. You would have to completely compress that crush large crush washer to strip the threads.

14 foot pounds may not seal these spark plug "crush washers"..All I'm saying..I tried it, wrench clicked and the washers were not even dented. As in, the plug may shake loose later..
Keep in mind that torque wrenches are not always perfectly calabrated. Most tech's go on feel and this is a fact and they are not going to pull out the torque Wrench for every screw they tighten...Not technically correct yet I think you know that by the book and what actually happens is quite different. I don't trust that 14 ft pounds is enough for these plugs maybe 17-18. then again I think I used too much anti-seize last time as well and it helped that one plug to shake loose.

Man4God

It is the 5.4. For some reason teh SOHC 5.4s have like 5 fewer threads than the 4.6 SOHC engines.

That is simply poor design on what is otherwise a super tough engine.

theizzardking

you only need the first 4-5 threads of a screw to get 90% of the tensile strength , a few less threads isn't going to hurt anyone.
think about how a bolt pulls on the threads of a hole, the 1st thread at the top of the hole gets the most force and the 2nd the 2nd and so on after 4-5 threads you're at about 90% strength for the bolt in most cases.

the standard rule of thumb is a threaded should be 1.5 times deep as the diam. of the hole to get 100% of strength. or 2 times with alum.

the design is good, there's something else going on here.
the only draw back of shorter threads is vibration issues which should be sorted by a lock or crush washer and a real tq setting of the bolt.


keep in mind that this is load bearing engineering data for pretty much everything (well not everything), the forces @ the spark plug hole should be way less than the tensile strength of the bolt/hole (spark plug) or surrounding material.


great reading for this sort of thing.

http://www.gizmology.net/nutsbolts.htm

eugenedbrooksiii

After having plugs come out quite loose I raised the installation torque to 17 ft-lbs, going by the feel of the washer crush. Plugs still don't "break" loose when I remove them, but they at least require a little wrench effort. On the most recent change the plug boxes indicated a half turn after washer contact, and it turned out that this is just what 17 ft-lbs produced.

Eugene

X-AWDriver

I know I'll be checking my plugs a little more often but a month later everything is buttoned up tight and no problems and I feel better after getting a look under the valve cover and the state of my engine appears to be real good after 153k miles.

IUEC'rnr

I know I'm a little late on this one..But..since i just changed my plugs today after 50k-and they look really good and are still gaped close-I found oil in the threads of #1. I then looked down the tube and saw a small amount of oil at the base.

My question is after reading this thread? Was it possibly the plug backing out as here or could there be another problem I dont really want to hear about going on.. I dont really remember if the plug came out easily or a little resistance

Replaced with the NGK and on their box it said to torque to 18-21 ft lbs. I just went with the extra .5 turn after seating the plug and adding some anti-seize

22RUCRAZY

I would say that your plug backed out . I like to go a good quarter turn past finger tight . Good luck

yotaman85

snap-on has a warranty that states if any of their torque wrenches ever runs off they will replace it guaranteed!

your spark plug was loose..