[ds968]

So while looking a couple of fairly comprehensive charts containing the various mfg prescribed wheel/lug torque for just about every make and model produced since the 60s, and with the overwhelming majority falling into the 80 to 100 ft/lbs area, except for a few heavy trucks being as high as 200, and furthermore with Lamborghinis and Ferraris capable of 200mph top speed having a recommended wheel torque of around 95, the Carrera GT stands alone at 407 ft/lbs !!! This is on two separate charts, from two separate sources so it's unlikely to be an error.. or is it..? If true, why is the GT's wheel so different than say and Enzo, or a Veyron, or a bunch of cars that are even faster, and almost as low as the Gt ?

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[flash]

a single big center nut, and not a pattern of smaller nuts?

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[94SilverCab]

An even more interesting question is, who has the time to investigate lug nut torque specifications???



You need a better hobby...



Jay

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[ds968]

" who has the time to investigate lug nut torque specifications??? You need a better hobby..."



Not really, but if you MUST know.. ;-)



I needed to find out what my wife's car specs were since I rotated the tires.. and have no clue where the manual is, thus the internet search for the fascinating topic of wheel torque.. once there, how can you possibly not look at Porsche ??!!

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[ds968]

nd , D'oh , if I had looked at images of the GT before posting I probably would have found the logical answer to that which Bob posted

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[jrsmitchell]

flash is right, any centrelock wheels will require much higher torque. The GT2 and GT3 are similar. There are a few companies that make special torque multiplier tools to get your wheels on/off without hurting yourself <img src="/forum/images/smilies/968/wink.png" class="smilie" alt="" /> For example: http://forums.RL.com/rennforums/997-gt2-...ation.html and http://www.youtube.com/watch?v=GzpTU7lBxBA

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[flash]

lol - i was just guessing, but the numbers made sense. i never really looked that closely at any of those cars, as i dislike them all, and they really don't hit my radar.

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[craigawoodman]

Yes, but is it a dry torque or a wet torque? Having to deal with larger wheel nuts (2,400 ft.lbs) for each of the wheel nuts on a Cat797 haultruck, the issue of "wet" torque (lubricated with grease or oil) or "dry" (no form of lubrication) is critical. If you apply a dry torque specification to a "wet" thread and nut (by using never-sieze or molycote, etc) - you are actually over torquing the thread.



Unfortunately some of these minor details become critical in some situations. Even a smaller Cat793 haultruck's wheel nuts are torqued to 650 ft.lbs (and there are 54 of them - from memory).

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[Cloud9...68]

Craig,



Interesting! Out of habit, I always give my wheel studs a quick spritz of WD40 before torquing them; it never occurred to me that I've been over-torquing my threads all these years. How much of an impact on the torque requirement does a thin film of a light oil like WD40 make?

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[flash]

yup



http://www.tpub.com/content/bridges/TM-5...-4_742.htm

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[Cloud9...68]

So I assume most, if not all, torque specs are for dry torque. Is there a rule-of-thumb offset for bolts that are coated with oil or anti-seize?

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[flash]

see the chart in the link above

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[Cloud9...68]

Ah, I see it now. Wow, that's quite a difference! Learn something new every day on this forum.

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[craigawoodman]

Cloud,



I would have said around 20%, but it is dependent upon thread pitch and depth, but it is a good rule of thumb (it seems a little high by Flash's chart). It is always good to determine if the thread is supposed to be pre-coated or not. Even WD-40 effectively makes it a wet torque figure (you only need a couple of microns of film thickness in there).



Also remeber - anything that is a "torque-turn" means that the stud or bolt is a use once and throw away situation. In this case you have either yielded or come very close to going over a very short cycle fatigue loading. This is where you tighten the nut to a specific value and then continue to rotate the nut 90 degrees or more beyond this point.

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[Cloud9...68]

"Also remeber - anything that is a "torque-turn" means that the stud or bolt is a use once and throw away situation. In this case you have either yielded or come very close to going over a very short cycle fatigue loading. This is where you tighten the nut to a specific value and then continue to rotate the nut 90 degrees or more beyond this point."



Does that mean the head studs need to be replaced any time the head is removed? That's a huge job...

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[craigawoodman]

Cloud - I am used to larger equipment, but technically - yes. It depends on the initial torque applied to the bolt and the amount of "turn" applied there-after.



Flash - has there been any instances of head bolts snapping?

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[flash]

i don't know about snapping, but i've heard about them backing off. max or pete would be a better source of info on that one though.

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[Cloud9...68]

My plan was to assemble the bottom end of my engine, then take it to a local shop to have it decked, which would require torquing the head nuts through a plate to simulate the presence of the head. Doing this would test the integrity of the studs. However, I'm suddenly concerned that this would potentially do more harm than good. Pete, or anyone else with experience assembling these engines - thoughts?

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[craigawoodman]

Flash - backing off would be similar to the stud yielding and then stretching with load afterwards. In this case however, with the stud torquing to an alloy head - it would be interesting to know what has the lower strength. Once again, depends on the initial torque (if high), then the stud is a throw-away item. If low, then possibly not.

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[Cloud9...68]

Here's what the manual says about tightening the cylinder head nuts: it's done in three stages, as follows:



1st stage: Tighten to 20 N-m (15 lb-ft)

2nd stage: 60 degree turning angle

3rd stage: 90 degree turning angle



I assume this means to turn an additional 30 degrees in stage 3 after the initial 60 degrees in stage 2, for a total of 90 degrees after the initial torquing. Interestingly, the torque value in the first stage must be a wet value, because the manual says to apply a thin coat of engine oil to the stud threads.



At any rate, the initial torque is very low, which implies (I hope) that the studs can generally be re-used.

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