Stuffing Box Maintenance

It happens every spring: Right after launching their inboard-engine-powered boats, owners are left wondering why they didn’t repack the engine shaft seal packing gland, also known as a stuffing box, during the off-season.

The stuffing box prevents (most) water from entering the hull while still allowing the propeller shaft to turn. The beveled glands force packing material against the shaft as the unit is tightened. A dedicated stuffing box wrench with straight jaws, like the one shown, is good at getting into cramped spaces.

The stuffing box prevents (most) water from entering the hull while still allowing the propeller shaft to turn. The beveled glands force packing material against the shaft as the unit is tightened. A dedicated stuffing box wrench with straight jaws, like the one shown, is good at getting into cramped spaces. Doug Logan photo.

It must be the drip, drip, drip torture you endured all last season as you anxiously watched the old seal leak a little too fast for your liking, the flax packing material having sacrificed itself as it is supposed to do. Now that it’s old and used up, water is filling the bilge, and numbing your mind as you constantly think, “I have to remember to repack that when I have the boat out of the water next time.”

It is possible to repack the gland with flax sealer while the boat is in the water, but don’t try it.  You run the risk of sinking your boat, particularly if you’re not experienced at performing this task.

So, as we come to the end of another summer and you start to think of hauling the boat for the winter, why not put the job of repacking the stuffing box at the top of your list of haul-out and winterization projects? That way you won’t forget it in the spring rush and endure another season of kicking yourself while the bilge fills up with water and the bilge pump works overtime to keep up.

There are different kinds of packing materials like the standard flax version (top) or the Teflon/ PTFE type below.

There are different kinds of packing materials like the standard flax version (top) or the Teflon/ PTFE type (bottom).

The chore is easy enough, with a little penetrating oil, a couple of pipe wrenches or a dedicated stuffing box wrench, a pick or corkscrew for removing the old worn out packing material , a small wire hand brush, a few rags,  and ten bucks’ worth of flax sealer. You can change the packing with about half an hour of labor—half of which is waiting for the penetrating oil to work. Usually the hard part is contorting yourself into the engine space to do the work.

There are different types and sizes of packing available. Some have Teflon or graphite added for improved lubrication. Do not use graphite on bronze shafts because it can cause galvanic corrosion of the shaft. Visit Western Pacific Trading, a major distributor of packing materials, for descriptions of the different types. You’ll need to know what size packing to buy (5/16″, 3/8″, etc.) and the easiest way to to that is to measure the size of the old packing, taking wear and compression into account. (This is another good reason not to try to do this job in the water.)

Here are my step-by-step instructions for repacking your stuffing box.

  • Lightly wire brush any corrosion off the stuffing box nuts.
  • Throw a rag over the transmission where the shaft connects to it so that you don’t get any penetrating oil on the transmission seals when you apply PB Blaster or other penetrant to the stuffing box.
  • Carefully apply penetrating oil to the stuffing box nuts and wait 10- to 15 minutes.
  • Using pipe wrenches or a stuffing box wrench, loosen the lock nut, then the female packing nut that holds the flax material. The nuts should loosen by turning the wrenches outboard and away from each other. In other words, the locking nut loosens when you turn it to the right as you look aft — you’re moving it away from the packing nut by advancing it along the threads. Note: use wrenches, not plumber’s pliers: You’ll be able to get the right torque and not gall the nuts by using proper wrenches.
  • Pick any old flax sealer out of the female packing  nut. You can use a pick or corkscrew. Follow with a 3M (not metal) kitchen scouring pad to clean the threads. Don’t use a tool that will gall the threads.
  • Inspect the rubber hose and clamps that connect the stern tube to the stuffing box. Replace as necessary using only 6-ply stuffing box hose (not exhaust hose).
  • Inspect the shaft and clean with emory cloth as needed.
  • Install the new flax seal. Most packing nuts will take three coils of new packing material. Make sure that at least four threads are showing on the nut for it to grab securely.
  • Cut the three coils of flax to circle the shaft exactly. Cut the ends at 45-degree angles so that they overlap when they meet instead of butting vertically.
  • Coat the packing coils with the green packing paste provided. I am not in favor of other packing greases some people recommend because many of these products contain graphite.
  • Seat the coils of flax seal in the nut, tamping them down with a blunt tool to avoid cutting or fraying the flax seal.  Each ring should have its end cuts offset from the layer below.
  • Tighten the packing nut until a very little bit of resistance is felt. Do not over-tighten! You should adjust the nuts again when the boat is in the water so you get the drip-rate right. Before the final adjustment run the engine in gear, allowing the seal to take a set (the packing nut should still be cool or just warm to the touch, not hot. You should be able to put your hand safely on the nut. Remember, the idea is lubrication, so if it’s  hot to the touch it’s probably too tight. At the same time, it should not be leaking copiously — just a steady drip.
  • Go slowly in tightening the seal, say a half turn of the packing nut at a time until it’s just right. Again, avoid over-tightening as the flax will take a set, and backing off it won’t work as well as slowly adjusting it.
You can use a 3M kitchen pad (not metal) to help scour out the threads of the packing nut. Doug Logan photo.

You can use a 3M kitchen pad (not metal) to help scour out the threads of the packing nut. Doug Logan photo.

Again, a stuffing box should drip at a regular, albeit slow rate of between two and six  drops a minute with the shaft turning. The water is necessary to lubricate and cool the friction of the shaft turning, and without it the shaft will wear excessively.

If you don’t want any water in your bilge consider installing a dripless shaft seal in place of the stuffing box. A dripless seal will cost more, requires that the shaft be pulled to install, and still needs occasional adjustment. I’ll go over installing a dripless shaft seal in a future blog. For now, be happy water is dripping in at a controlled rate, and the stuffing box is working as it should.

 

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