Date: Sun, 4 Feb 2001 16:22:00 EST
Reply-To: NotaJeep@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Steven Denis <NotaJeep@AOL.COM>
Subject: Re: Lug nut lubrication or not?
Content-Type: text/plain; charset="US-ASCII"
In a message dated 2/4/01 11:33:49 AM Eastern Standard Time,
gstearns@OPTONLINE.NET writes:
<< For years I've been using anti-seize on lug nut threads and contact
surfaces. I feel that I always get an accurate torque spec this way.
Recommended or not, it is just good practice. >>
Oh Kaaaaaaay..
Let's get this straight.
#1 I'm employed as an "engineer" but I ain't one, really..at lest not the
mechanical type..so if anyone here qualifies, I'll bow out.
#2 Torque specs. (good ones) to tell you what (if) to lubricate the treads
with. They assume clean and dry if they don't (always assumed clean!!!)
Let's look at what we are doing when we are putting the wheel back on the van
(other than trying to stay dry and not get hit by the semi's blasting down
the interstate behind us)
LOOK at the wheel where the lug meets it. it's rasied up.When you tighten the
bolt down you are deflecting the wheel ..it is "spring-y" right there.. So,
if the bolt has the proper tension on it, as the wheel takes up load and the
load is relived, the stud and wheel with "give" but not so much that it
overcomes the clamping force of the stud/bolt. This is how "spring" or
"warpy" washers work to lock fasteners.. here we use the wheel as the
"spring". If you don't get enough pressure you get motion between the parts.
Not good..the shock loading and the pressure going above and below the
clamping force allows the nut/bolt to come loose. and that is not good..
If you OVER tighten the lug nut/bolt you can and will exceed the elastic
limit of one or both parts.. the "spring" is gone...now the fastener is
statically loaded to 95% of it's yield strength. Add the running loads?
oops!...
The torque setting for the fastener is a way to translate the clamping or
stretch force applied by the fasterner. IF you lubricate the threads and the
spec. is for dry threads? you are over tightening the fastener!. I have seen
pressure vessels fail due to some dimwit taking and putting lubrication on
the threads. as the bottle "pressure cycles" the over-stressed (over
stretched) neck failed..nobody died, but that part was only luck!
SO why the big deal on the alloys?..Well they DON'T have the "give" of the
steel wheels! the "preload" is due to the "crush" of the aluminum..the
material itself is elastic. so it's MUCH more critical to get it right. On
the steel wheels you have , oh, say up to maybe 1/8 inch before the wheel
"bottoms out" on the hub..with the alloys you have a matter of thousandths
between proper crush and over stressing the part.
Saying that, I too use never-seize and a torque wrench..but I run the
"forgiving" steel wheels....I KNOW I'm over tightening them.....
steve
"Hey! nice Jeep, Mister! "
"Look kid, it's NOTAJEEP! "
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