planejim(at)bellsouth.net
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 Posted: Mon Feb 18, 2008 5:59 am Post subject: Torque of 3/16" or An3 Bolts |
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Zenith Listers,
do not archive
I have been following the "Bolt Torque" subject with interest. It has been
my experience ( for a little over 51 years now ) that folks with limited
experience tend to "over torque" those little 3/16" diameter ( AN3 ) bolts
which are used through-out our airplanes. You know - if tight is good,
tighter is better! I've seen others just wring them "right off". The worst
situation is the "over tightened" bolt that hasn't sheared "YET", especially
if it is in a critical location.
Of course a properly calibrated torque wrench of the correct size is the
proper way to go, but I must admit this old mechanic doesn't alway use one.
Many times, the particular installation will have the very definite
specified torque for the particular bolt called out in the manual or
instructions being used, such as gearbox or engine buildup. However, most
bolts will be "torqued/tightened" using just industry standards, such as in
AC 43.13-1.
Of course there will be those "special" installations such as the Zenith
rudder pedal bearing support installation being discussed. Probably, the
best case here would be that the "kit supplier" specify what to do in these
"special" situations. ( One may be a "hinge" where rotational movement is
involved - here we usually use a castleated nut. ) However, I suspect that
this will not be the norm with "most" kit suppliers.
Just sometimes, we must do a little thinking for ourselves. If the rudder
"torque tube" must rotate in the bearing support, we should give it some
thought on our own. If in doubt, seek the guidance of a experienced mechanic
or builder or even better the experts at the kit supplier, such as Roger or
Nick at Zenith.
If you are fairly new at this, I suggest you get a proper torque wrench and
some 3/16' bolts and NEW fiber lock nuts ( since that is what we use the
most of, except in the engine compartment in some places ) and practice
torqeing some of those bolts. I think you'll br surprised how little effort
it takes.
One final suggestion: use just a 1/4" drive wratchet rather than a 3/8"
drive wratchet when installing 3/16" diameter bolts using self locking nuts,
IF you are not using a calibrated torque wrench. You will tend to over
torque or stretch those little bolts with that "big" 3/8 drive ratchet.
Practice makes perfect!
Jim Hoak - 601 HD
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