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Stuffing Box MaintenanceWhile stuffing box replacements such

as the Lasdrop (BB, October 1984)and Lowell Zabel’s homebuilt system

(BB, March 1985) are likely to proveincreasingly popular in the future,

most boatowners with inboard

engines must deal with the realities of the conventional stuffing box. While

the stuffing box is relativelyfoolproof, it does require routine

maintenance to operate properly, andto avoid damage to drive train com-

 po ne nt s.The most common complaint

about stuffing boxes is leaking, andthe most common cure is to torquedown on the packing nut a few more

turns. While this may serve to stopthe 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, you

s q u e e z e the flax packing tighter against the shaft. While the flax may be softer than the shaft, it can wear a

groove into it over time. The groovelets 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 minimumamount of routine maintenance, using

 perhaps a half hour once a year whenthe boat has been hauled, and pennies

of material.How do you know when to repack 

the stuffing box? Just assume that it

needs it now. If the packing is a year old or more, you won’t be wastingyour time to replace it, since the job isso simple.

The accompanying drawing shows

a simplified cross section of a typicaltraditional stuffing box. No matter 

what refinements are seen between

competing brands, the basic designand principle is the same. The shaft is

sealed by compressing a soft materialagainst it, using a hollow nut. Themore you tighten the nut, the morethe 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 of the shaft. Water gets around the pack-

ing, so you tighten down some moreon the packing nut. The packing getssmaller and harder, and presses

tighter and tighter on the shaft. That

nice, soft packing is now hard enoughto wear a groove in your propeller 

shaft.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 calledroutine maintenance.

Whatever that frayed, dried-out

material looks like that you removefrom the stuffing box, it probably

 began life as square flax packing. This

is a square plaited material, im-

 pregnated with a waxy, oily organiclubricant. It comes in various sizes

from l/8" up to 1/2   “. To determine

the size you need, measure theclearance 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, thestuffing box is located in a dark, tiny place under the cockpit, which may

 be accessible only by standing onyour head in a cockpit locker. In some

cases, there is li ttle clearance betweenthe transmission coupling and the

stuffing box, making life even moredifficult. That’s why stuffing boxes

get neglected, and that’s why shafts

get worn out.

First, back off on the lock nutwhich holds the stuffing box adjust-ment. It’s only necessary to back off a

little. Next, back the packing nutcompletely off the threaded neck of 

the 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