Rule of thumb that I have always operated by is; unless the instructions
specfically state dry threads always use at least a light oil (I always put a
littel grease under the head of the bolt or nut too). This came from an
aircraft mechnics pocket hand book I had.
My first job out of college was at Pratt & Whitney Aircaft and my first job was
to develop torqueing specs for the F100 engine. Even a fastener that feels
smooth going together by hand can have as much as a 40% variation in the
clamping force when dry. A light oil will reduce the variation down into the
20% range in most cases.
I ran into a situation at another job where the ANSI grade B8 bolts torqued to
75 ft-lbs would allow a pressure vessel to pass the proof pressure test but the
same vessel assembled with 17-4PH alloy bolts (needed to prevent stress
corrosion in off shore drilling rigs) would leak. I rigged up a fixture in the
tensile tester in the lab and I found I needed to torque the 17-4PH bolts to
130 ft-lbs to get the same clamping force as the B8's at 75 ft-lbs. A number of
differnt lubricants were tried without success and having two torquing
requirements in a production environment was not desirable. What I wound up
doing was plating the 17-4PH nuts with zinc. The zinc acted as a lubricant and
prevented the galling that was happening with the 17-4PH to 17-4PH. 75 ft-lbs
on this combo now produced the same clamping force as the B8 and no leaks.
Dave Clement
99 SLT+ CC 4x4
In article <73C8ABBE-5DBC-11D9-9FDA-000393129EB2@tepidcola.com>,
dml@tepidcola.com (Michael Maskalans) writes:
>
>
>
> On Jan 3, 2005, at 09:21, Josh Battles wrote:
>
> > "Eric Huff" <mopar@ehuffy.com> wrote in message
> >>
> >> I just went out and retorqued the spindle nut. I even oiled the
> >> threads lightly first, but the bearing is still loose.
> >>
> >
> > Just a word of caution here... If you removed the spindle nut instead
> > of
> > just re-tghtening the thing while it was still on there, you're going
> > to
> > have to probably replace it. They're one time use only items, and
> > once you
> > crush that nylock ring, it's game over.
>
> as long as we're picking nits,
>
> torque ratings are also only good for clean, dry threads. they take
> into account the friction of the threads, so oil or grease in the
> threads will increase clamping force (and resultant stresses on threads
> and shanks) for a given radial torque and thread locker or dirt or
> anything else "sticky" will do the opposite.
> --
> Mike Maskalans <http://mike.tepidcola.com/dodge/>
> '98 Dakota SLT 318 4x4 SFA & 35s
> '84 RamCharger Royale SE 360 4x4 stock
> mobile.612.618.4652 home.585.935.7129
>
This archive was generated by hypermail 2b29 : Tue Feb 01 2005 - 00:18:30 EST