Stuffing Box Maintenance While stuffing box replacements such as the Lasdrop (BB, October 1984) and Lowell Zabel’s homebuilt system (BB, March 198 5) are likely to prove increasingly popular in the future, most boatowners with inboard engines must deal with the realities ofthe conventional stuffing box. While the stuffing box is relatively foolproof, it does require routine maintenance to operate properly, and to avoid damage to drive train com- po ne nt s. The most common complaint about stuffing boxes is leaking, and the most common cure is to torque down on the packing nut a few more turns. While this may serve to stop the leaking, it may also result in damage to the propeller shaft, par- ticularly if the shaft is bronze. When you tighten the packing nut of a conventional stuffing box, yo u squeeze the flax packing tighter against the shaft. While the flax may be soft er than the shaft , it can wear a groove into it over time. The groove lets in water, and you tighten the packing nut even further to eliminate leaking, exacerbating the cycle. The possibility of leaking and shaft wear can be avoided with a minimum amount of routine maintenance, using perhap s a half hour once a year when the boat has been hauled, and pennies of material. How do you know when to repackthe stuffing box? Just assume that it needs it now. If the packing is a yearold or more, you won’t be wasting your time to replace it, since the job is so simple. The accompanying drawing shows a simplified cross section of a typical traditional stuffing box. No matterwhat refinements are seen between competing brands, the basic design and principle is the same. The shaft is sealed by compressing a soft material against it, using a hollow nut. The more you tighten the nut, the more the sealing material is compressed against the shaft. Over time, the packing dries out, A typical stuffing box installation and is worn away by the turning ofthe shaft. Water gets around the pack- ing, so you tighten down some more on the packing nut. The packing gets smaller and harder, and presses tighter and tighter on the shaft. That nice, soft packing is now hard enough to wear a groove in your propellershaft. In an emergency, almost any com- pressible material can work in a stuf- fing box, but we’re not talking about emergencies here. We’re talking the boring , but essential thing called routine maintenance. Whatever that frayed, dried-out material looks like that you remove from the stuffing box, it probably began life as square flax packing. This is a square plaited material, im- pregnated with a waxy, oily organic lubricant. It comes in various sizes from l/8" up to 1/ 2 “. To determine the size you need, measure the clearance between the shaft and the inside of the packing nut. Do this as carefully as possible, for having exact- ly the right size packing makes life easier. Removing the old packing may re- quire some gymnastics. Usually, the stuffing box is located in a dark, tiny place under the cockpit, which may be acces sibl e only by stan ding on your head in a cockpit locker. In some cases, there is li ttle clearance between the transmission coupling and the stuffing box, making life even more difficult. That’s why stuffing boxes get neglected, and that’s why shafts get worn out. First, back off on the lock nut which holds the stuffing box adjust- ment. It’s only necessary to back off a little. Next, back the packing nut completely off the threaded neck ofthe stuffing box. The next job is to dig out the old The packing nut is backed off, and the old flax packing removed
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New packing is carefully cut to lengthand inserted into the packing nut
packing. The ideal tool is thin, so thatit can be slipped between the shaft
and the packing nut. It has a hook onthe end, so you can grab onto the old
flax packing. And it’s soft enough notto score the shaft while you’re dig-
ging around. Frankly, we’ve never found that ideal tool. Instead, you can
settle on a farily long, thin screw-driver, which will do the job if you’re
careful.Be sure to dig out all the layers of
packing. The last one may be so hard
that it’s difficult to distinguish fromthe bronze packing nut.
If you’ve scratched the shaft, or if
it’s heavily oxidized, it’s a good ideato polish the shaft where the packing
will rest against it. You can do this
with fine silicon carbide (wet or dry)
The packing nut is only hand-tighteneduntil the boat is launched
sandpaper, used wet. When the shaftis clean and bright, thoroughly washit with water to eliminate all traces of
abrasive, which could quickly score
the shaft if not removed. Then, greasethe shaft lightly to make it easier toslide the repacked nut into position.
The packing should be installed in
layers, rather than a continuous spiral.The length of each piece of packing is
fairly critical. There should be no gapat the ends when the packing is wrap-
ped around the shaft. Use as many
layers of packing as will fit in the packing nut and still allow the nut to be threaded onto the neck of the stuf-
fing box. Gently force each layer into
the packing nut with a screwdriver, being careful not to cut the packing.
Stagger the joints in the layers of packing, so there is no possibility of
leaking. When the packing nut is full- there should be a minimum of
three layers of flax packing - tightenthe packing nut by hand as far onto
the neck of the stuffing box as youcan. Then, back off on the nut, andcheck the packing to see that it hasseated evenly inside the nut. It maynow be possible to add another layer of packing, if the layers have com- pres se d enough .
Retighten the packing nut by hand.
Do not use a wrench or pliers. The
packing nut should only be tightenough to stop leaking. Any tighter,and you risk damage to the shaft, andgain nothing.
When the boat is launched, im-mediately check the stuffing box for
leaking. If there is leaking, use awrench to tighten the packing nut,
but only until the leaking stops - nomore. Then, tighten down on the lock
nut, using two wrenches - one tokeep the packing nut from beingtightened down further, one totighten the lock nut.
Run the engine with the gearbox
engaged. A slight drip - one dropevery minute or so - is fine, but not
necessary if the box is adjusted justright. Keep an eye on the stuffing box
for a while, as it may develop a slight
leak as the packing wears in. If a leak develops, tighten slightly - veryslightly.
There is no hard and fast rule abouthow frequently to repack a stuffing
box. On the average sailboat, theengine rarely gets enough hours toactually wear out the packing. But packing does harden over time, and
its effectiveness is reduced. You’re better off repacking based on the time
since it was last done, rather than the
number of hours the engine has beenrun.Unless your sailboat spends a lot of
time under power, you can get away
with repacking every other year.Powerboats will minimize the risk of shaft damage by repacking yearly.
Repacking the stuffing box isn’tvery glamorous, but it’s an essential part of routine maintenance. Neglect
it, and we guarantee you’ll regret it,since a dollar’s worth of flax packingis always cheaper than a new shaft.
After launching, use pliers or a wrench
to tighten the nut slightly if there isany leaking