| Enginetype: Inboardgas > motormodel: atomic four
> Serialnumber: 1970's
> Configured: single
> boatmodel: Erickson 27
> Boatlocation: long beach, ca. salt
> Need: re-tightening packing nut
> TechQuestion: need diagram and
directions for replacing packing and re-tightening packing nut.
our answer:
The packing is not a
bearing. It's only purpose is to seal the hole where the prop shaft
comes through the bottom of the boat. Shaft support is done by the
transmission and the strut/cutlass bearing, located in front of the
prop. If you are not sure when the packing was changed last, and it is
leaking, it is best to replace the packing and start over so you can
monitor it's wear pattern.
There are several types
of stuffing box, (sometimes called a shaft log) so I will use the most
common for example. They are all maintained about the same way. Also,
the packing material diameter is very important. It has to match the
original packing material diameter, as specified by the shaft log
manufacturer. Sometimes a little trial and error, in selecting the
size to use, is called for. You can use one of the old packings to
match. That's if the one in there is the correct one in the first
place.
The correct diameter
packing material will fit relatively snugly into the packing nut. Too
small a packing will not seal properly and too large will allow only
two strands to be inserted.
After loosening the
packing nut and jam nut, (see diagram:) you can then pull the
old packing from the packing nut. Use a pick or hooked pick to remove
all of the old packing. There is usually three strands of packing
installed but look for more and there could be only two.
After you have removed
the old ones, cut three new packings by wrapping them around the shaft
and with a razor blade cut the packing so that each one is exactly the
circumference of the prop shaft. Then insert them carefully, one at a
time, into the packing nut, making sure that you stagger the packing
seams at 120 degrees. After each packing you may want to run the
packing nut onto the stuffing box, as an aid to getting the packing
all the way down into the packing nut.
Square style braided
packing is suggested for shaft and rudder boxes. This material is made
of all natural compounds; it resists heat build-up and will not score
or mar the shaft. Graphite impregnated packing is not recommended
because it can cause galvanic corrosion of the shaft. Teflon "
impregnated packing, while affording excellent water-seal capability,
can mar the shaft through friction. Use flax packing impregnated with
animal fat, both materials known for their resistance to breakdown
from heat, with an excellent performance record over many years and
applications.
A break-in period is
recommended on all new installations, during which excessive water
leakage is allowed for two hours. This water flow allows the packing
to conform to the surface finish of the shaft, and water to infiltrate
all the voids of the packing for effective heat dissipation even after
the unit has been tightened to its final seal. One drip or two per
minute is considered normal leakage.
This page is not
currently linked to the web site. Be sure to save it if you want to
view it later |
