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Overtightening spark plugs in aluminum heads...

Discussion in 'Technical Q&A' started by Kevallino, Nov 4, 2004.

  1. Kevallino

    Kevallino Formula 3

    Feb 10, 2004
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    Kevin
    ...is apparently what caused my 348 to barf a plug last Saturday after a magnificent day out with the SoCal Ferrari Driving Club. Fortunately I was less than 5 miles from home (although 40 miles from the bloke who looks after my car) so organized a flatbed and called Mrs. Kevallino to come collect me.

    Apparently you can ream the hole (please, folks) and install an insert without removing the head but of course there is that risk of a big enough piece of metal dropping in to the cylinder. So I am going with the big-dollar option and having the engine pulled so the work on the head can be done off of the engine, with the "advantage" of having all of the other usual suspects checked at the same time. I love this car but am losing a bit of confidence with regard to its prior maintenance history, so am buying myself some piece of mind.

    So just letting everyone know not to get too ambitious with the spark plugs and don't let your mechanic overtighten either.

    Cheers
    Kevin
     
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  3. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
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    'Helicoil' is the term, probably doesn't leave any more shavings than the factory did!!!!
     
  4. Smiles

    Smiles Moderator
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    Nov 20, 2003
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    Except that the factory didn't tap the threads with the heads in place!

    Good warning, Kevin. Thanks.

    Another tip is to use anti-seize when installing plugs into aluminum. Backing out galled plugs can be a problem, too.

    --Matt
     
  5. Rifledriver

    Rifledriver Two Time F1 World Champ

    Apr 29, 2004
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    If the helicoil tap is heavily greased it will trap and hold the shavings. It's done all the time. I wouldn't pull the head for that.
     
  6. BigTex

    BigTex Seven Time F1 World Champ
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  8. Kevallino

    Kevallino Formula 3

    Feb 10, 2004
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    Thanks for the info - I've discussed that with the bloke who works on my car but frankly have kinda been looking for an excuse to have him look over the whole car anyway. I was on the bubble as to whether to do the whole enchilada because of the price difference but in looking at what few records I have of the prior service on the car I have decided to get some bang for my buck while he has the engine out and check the water pump, tensioner bearings, etc. My car was represented as having had a 30K service but the backup is a bit sketchy so as I said I'm buying a bit of piece of mind at the same time.

    Not cheap peace of mind, mind you, but I do find myself driving this car bloody hard so want the confidence to keep visiting the 7,500 rpm neighbourhood over and over again!!

    Cheers
    Kevin
     
  9. jeffdavison

    jeffdavison F1 Rookie
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    Another thing to worry about is re-using or reinstalling the plug multiple times.
    The thin wall of the threaded body develops internal stresses that can cause failure to occur, leaving the threaded section in the head.

    This migh be a rare occurance, but it did happen while I was "properly" torquing a plug down for a third time:

    JD
     
  10. bernardo66

    bernardo66 The Crazy Cat Man
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    Dec 14, 2003
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    Never have I installed a plug without this stuff. It works wonders.
     
  11. bernardo66

    bernardo66 The Crazy Cat Man
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    Dec 14, 2003
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    I change my plugs on all my cars, on an annual basis. The cost is negligible, and the aggravation (of something like this happening) saved, is priceless.
     
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  13. yelcab

    yelcab F1 World Champ
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    If you are going to pull the head, I would think a Timecert spark plug repair insert is better and provide more strength than a pure helicoil.
     
  14. Kevallino

    Kevallino Formula 3

    Feb 10, 2004
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    Thanks - when I spoke to my mechanic he did mention using something specific. Don't have it to mind at the moment, but I believe it had to do with the metal the insert was made out of. I will check with him to see what he had in mind.

    Cheers
    Kevin

    BTW not sure if this was clear but this wasn't MY fault - happened as a result of whomever used to have the car and/or worked on it. Hence my decision to "go large" with the repairs simply because I don't trust the previous work that may or may not have been done. KFH
     
  15. dapper

    dapper Formula Junior

    Nov 10, 2003
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    Dave
    Just swapped my plugs out for the first time in my ownership. I found it took real balls to go right up to that specified Workshop manual torque figure even with the anti seize lubing the thread!

    That failed plug pic, doesn't look like any of the normally recommended types?
     
  16. dhs-9

    dhs-9 Formula Junior

    Feb 6, 2004
    292
    I put anti seize on mine and only tightened them up to very snug I was afraid of stripping the theads. You know how it is just a little more as you turn the wrench and next thing you know they start spinning easily.
     
  17. kaamacat

    kaamacat Formula 3

    Jun 13, 2004
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    JeffD..........Two questions for you. 1) What are the torque specs they have for the plugs on your car (just curious because usually its minimal), and 2) I noticed the base was not tapered, so, I was then looking for some form of crush ring. Are they literally just a flat base plug against the heads?


    Bob
     
  18. jeffdavison

    jeffdavison F1 Rookie
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    The precise torque spec provided by the plug manufacture is a bit cloudy. See the attached pic. If the plug has been in and out a few times the physical torque to tighten would probably be greater due to the crush ring being compressed multiple times. Taking a plug in and out is common if you're checking if you've the proper heat range for your driving, mods, etc...

    I now will abide by the new self mandated rule of never using a plug if it's been in and out more than twice.


    I didn't put the crush ring in the picture. The plug DID come with one. It fell off when I remove the plug, and just didn't bother to put in front of the camere when I shot the pic.

    JD


     
  19. PSk

    PSk F1 World Champ

    Nov 20, 2002
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    21 ft-lbs for alloy heads, 25 ft-lbs for cast iron heads, or is it lbs-ft ... :confused:

    What my father (30+ years as A grade mechanic) has taught me to always use and I always torque spark plugs to these settings.

    I wouldn't use that NGK method myself, how do you know it has seated properly before you do the 1/16th of a turn?

    Pete
     
  20. valvespring

    valvespring Rookie

    Dec 21, 2003
    18
    Lb-ft is torque, ft-lb is work.
     
  21. ferrarifixer

    ferrarifixer F1 Veteran
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    The torque depends on the thread size, and material. In cases of high silicone content alloy such as Ferrari cyl heads, I follow this rule of thumb....

    14mm (308) 18lb ft new. 16 lb ft used.

    12mm (328/TR etc) 16 lb ft new 14 used.

    10mm (355/F40) 14 lb ft new 12 used.

    All of this is irrelevant if using taper seat plugs (no Ferrari). But as an example 16mm into cast iron for taper seat plug is 7 lb ft .

    To repair a stripped thread, I think a Time sert is better than a Helicoil, but either are acceptable, and both can be done with the head in situ, some grease and a powerful wet/dry vacuum cleaner with a bit of hose to fit through the plug hole.
     
  22. peterp

    peterp F1 Veteran

    Aug 31, 2002
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    I think the owners manual of my 3.2 says for new plugs it should be torqued to 15 lb-ft, then loosened and retorqued to 12 lb-ft. I will confirm when I get a chance to check the OM.
     
  23. kaamacat

    kaamacat Formula 3

    Jun 13, 2004
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    Jeff...thanks for the pics and info........ I've almost always done what the pic shows, tapered I put in just until the base touches, back out a little, in again, then 1/8turn. On the others with the crush ring, those I usually trash just because once installed Im not sure you get the same install torque the next time. (but who knows).

    Hey, either way, a great help is to (if you are room limited) put a 4" piece of hose over the plug so it wont drop..

    (BTW.......How did you (or I should say your car, like the Iridium's?)



    Bob
     
  24. jeffdavison

    jeffdavison F1 Rookie
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    My F355 has taken very kindly to them! :) :) :)

    Btw.. it was "fun" getting the threaded body out of the spark plug hole. Used the skinney end of a mill bastard file and turned it counter clockwise. Luckily the anti-sieze compund made it fairly easy to just unscrew it, and luckily, the piston was not so near tdc. (I didn't have an easy out handy)

    Jeff Davison
     
  25. Lawrence Coppari

    Lawrence Coppari Formula 3

    Apr 29, 2002
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    Units in engineering follow the communtative rule of mathematics which means a*b = b*a. A ft-lb is the same thing as as lb-ft. It is semantics and personal preference only. Both are correct.

    One form of energy is kinetic energy. Mathematically, it is 1/2 * W/g * V**2

    The units are lb/(ft/sec**2)*(ft/sec)**2. Cancelling like units you end up with lb-ft for energy. But ft-lb is also correct because the order of the formula can be written in any order and provide the same numerical result. In engineering computation the purpose of units is to ensure you have the correct formula and are comparing apples to apples.
     
  26. yelcab

    yelcab F1 World Champ
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    I say tomato, you say tomAto

    It is the red fruit (veg) that you put in your salad.
     
  27. Ken

    Ken F1 World Champ

    Oct 19, 2001
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    Um, I use a VERY thin coating of Phil Woods green bicycle grease. Is this okay? It's worked well for me and I had a period of very frequent plug changes.

    Ken
     
  28. valvespring

    valvespring Rookie

    Dec 21, 2003
    18
    Of course multiplication commutes, but I disagree that "it is semantics and personal preference only." The customary U.S. unit of torque is lb-ft. The customary unit of energy and work is ft-lb.

    Torque is a vector product. Work and energy are scalar products. In the SI system, the distinction is made by referring to the vector product as "newton-meters" and the scalar product as "joules." In the U.S. system, the distinction is made with the lb-ft / ft-lb convention.
     

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