life, and using an old seal with a new pump is a false
economy. The seal can be difficult to remove, so it usually makes sense to remove the pump spacer from the
engine so that the seal can be removed on the bench.
Thanks to some “questionable” engineering, installing a new vacuum pump can be very tricky. There is
a single infamous nut on the mounting flange that
cannot be reached with traditional tools. Mechanics
have developed all sorts of specialty tools and tricks
over the years to get this nut on and off. They range
from the crude but common screwdriver-and-hammer
approach to special vacuum pump wrenches that make
it possible, but not completely simple, to reach this
nut. The Tempest name comes to mind again because
its version of this wrench includes an integral magnet
that helps prevent the nut from falling into the cowling. The easiest way to get at the nut is to remove the
magneto. However, if you do this, be sure to plug the
open hole in the accessory case with a rag. A single nut
or washer falling into the accessory case will ruin your
whole week.
There are also a bunch of tricks out there for getting
the nut started on the stud during installation. Bob
Booth, of Aircraft Services in New England, taught me
my favorite. Since you cannot reach this area with your
hand, you need some other way to get it on. Begin by
If the pump is not properly protected
while washing the engine, oil and sol-
vents can enter through the exhaust
port and induce pump failure.
cutting a 1/4-inch-wide strip of electrical tape about 8
inches long. Wrap the tape around the perimeter of the
nut about four to five times clockwise. Leave a tail of
about 6 inches to hold on to. Using a right-angle pick,
carefully place the nut at the end of the stud. Next,
slowly pull on the tape while lightly pressing the nut
against the stud with the pump body. A few turns and
it’s threaded on the stud. Spin it to the base and use a
pump wrench to finish the job. Although you may have
seen others using a screwdriver or a chisel and hammer
to “tap” the nut and tighten it, this is not the right way
to do it. Use the right tool for the job, period.
Depending on the situation, hose fittings should be
installed when holding the pump, or while the pump
is on the engine. Never use a vise, and never use Teflon
tape on the threads. Just install the fittings hand-tight,
and then use the box end of a wrench for no more than
a single turn.
