Bookmark and Share Email this page Email Print this page Print

Stuffing box inspection and replacement

Apr 25, 2017

The stuffing box is a critical part of the boat. It allows a driveshaft to spin through the hull without allowing water to pour into the vessel. These units are often deep down in the boat, behind the engine and with limited access. On many sailboats it is often under the cockpit with side access through a locker — a dark and damp place often forgotten about until the bilge pump kicks on every few minutes and one wonders where the water might be coming from.

After removing all that resides in that locker, crawling inside and removing the small access panel — perhaps head first — the stuffing box becomes visible. Maybe it has been a few years since your last visit, but did you remember to bring two large stuffing box wrenches and a flashlight? To adjust the traditional stuffing box, you need two wrenches in order to loosen the backing nut off the cap nut. This requires two hands in this small space as well as being able to see what you are doing while breaking the nuts free. These nuts are tight and some two-handed muscle is required to free the nuts from their grip on each other. Proper wrenches are key; the adjustable stuffing box wrench might work for you, but a proper toolbox should include a set of fitted stuffing box wrenches to avoid a lot of pain and frustration.

If you succeed here, the job of adjusting the stuffing box is fairly straightforward: Tighten up the cap nut until the water stops gushing in, then retighten the two nuts together. More often than not, these nuts are corroded and, without proper tools and leverage, a tough nut to crack.

Now it’s time to crawl out of the locker, start the engine, put her in gear and re-enter that locker (don’t forget your flashlight) to see how the adjustment holds up in motion.

The stuffing box should drip ever so slightly now, say a drop every five to 10 seconds. No drip is no good because without a little bit of water lubrication, the shaft will heat up and wear over time, creating a groove in the shaft that no amount of packing can stop anymore. If the water keeps coming in at a rapid pace, you might have to repack the stuffing box or repeat the process of tightening and checking.

Don’t adjust the stuffing box while running the engine in gear! Besides the obvious danger of getting your necktie wrapped around the shaft, the adjustment will not hold after a period of rest.

On larger sailboats and trawlers, the access to the stuffing box or boxes might not be a problem and adjustments can be made while sitting down and with good light. In these cases, the traditional stuffing box is a simple, well-proven maintenance item. However, if the stuffing box is as hard to reach as described above, a dripless stuffing box might be the solution.

The dripless stuffing box does what its name suggests, leaving you with a dry bilge and, more importantly, with a low-maintenance stuffing box. No big nuts to adjust in tight spaces with big tools, no packing to replace with tweezers in this dark corner of the boat while hanging upside down in a rough sea.

The expense of refitting a dripless stuffing box is well worth it if it is installed by the boatyard, but with the proper tools, this job can be done by the handy boatowner as well.

Start by removing the prop outside the boat and the set screws in the shaft coupler inside the boat. The goal is to pull the shaft out of the coupler far enough to remove the old stuffing box off the shaft log. A shaft puller is the ideal specialty tool for this job — the dead weight of the slider jars the shaft out of the coupler in a few minutes. With the shaft pulled out of the coupler, the old stuffing box can now be removed and the shaft and shaft log can be examined.

To order a new stuffing box, the shaft size and shaft log’s outer diameter need to be measured. For example, in this case it is a 1-inch shaft and a 1.75-inch shaft log. Clean and wet sand the shaft on the surface that will receive the new stuffing box and examine it for burrs and grooves. If the shaft shows severe grooves from an overheated stuffing box as described above, there is a chance that the new stuffing box will leak (more on that later), or maybe a new shaft is needed after all. The new stuffing box by PSS comes with three key components: a nitrate bellows, a stuffing box with carbon graphite flange and a stainless steel rotor. The rotor will be attached to the shaft and turn on the graphite flange to create a watertight seal by compressing the bellows with the rotor. The polishing of this stainless steel rotor on the graphite flange with the water nearby makes for a virtually maintenance-free seal.

Install the bellows onto the shaft log and tighten the hoseclamps. The 3/8-inch nipple will point up. Connect a piece of 3/8-inch marine-grade fuel line to it, double-clamped, and run it 2 feet above the waterline. Secure this hose along the way — if it were to fall into the bilge, this vent hose would become a fill hose.

Take the rotor and pre-position a set screw in each of the two holes with a drop of thread lock. Position the shaft so the stainless steel rotor can be installed onto the shaft. This is the tricky part because the rotor has two rubber O-rings inside it that must not get damaged during this installation. That’s why wet sanding the shaft is so important. Use soapy water — not grease or penetrating oils — to slide the rotor onto the shaft. Lock the shaft into position, as it will want to walk out while you are trying to push the rotor on. Use lots of soapy water and move the rotor at least an inch past the keyway of the shaft. Prepare the key and keyway, and reinstall the shaft into the coupler. Careful tapping will position the shaft and line the key up properly.

 The shaft puller can now be used in reverse to re-install the shaft into the coupler to its old marks. The set screws can be wrenched down and seizing wire should be added. The prop can also be reinstalled. Now, the final touch on the stuffing box: The stainless steel rotor needs to be slid down the shaft to press upon the carbon graphite flange. The rotor will compress the bellows, but how much will depend on the size of the shaft. In this case, three-quarters of an inch of compression is needed for a 1-inch shaft. Mark the shaft at the point of touching just the flange, slide the rotor another three-quarters of an inch onto the shaft and tighten the set screws down. Here is the part were those old grooves on the shaft can be a problem. Test that last three-quarters of an inch and see if the groove is interfering with the rotor. Moving the bellows up or down the shaft log can relocate the final position of the rotor on the shaft. If all looks good, add the second set of set screws with thread lock glue on them as well.

When the boat is launched and commissioned, inspect and run the engine in gear and observe. The rotor and the graphite will make a perfect seal almost immediately, but a little spray might occur occasionally. It should stop after a minute — if not, a bit more compression might be needed. A poor engine alignment can cause the shaft to shake a lot and make the dripless stuffing box drip.

The stuffing box is now a lower-maintenance item and can be quickly inspected and cleaned with one hand, even if upside down in that locker.

Edit Module

Old to new | New to old
Apr 25, 2017 04:11 pm
 Posted by  Alex Agnew

Paul Mirto has some fine illustrations of the stuffing box and associated gear at his website and in particular at this location:

http://mirtoart.photoshelter.com/image?_bqG=2&_bqH=eJxzdcr1NjD2rkourjAy1C0zNDfJzDNw8_X1qSi2sgBCQwMgsPKMdwl2ti0uKU1Ly8xLV_OMDw12DYr3dLENBUk7OmcZp7u4hlWlRarFOzqH2BanJhYlZwAA5kUb3w--

Apr 25, 2017 04:14 pm
 Posted by  Alex Agnew

If you can't see that last link, try this one;
https://goo.gl/TXibZc

Apr 26, 2017 08:13 am
 Posted by  Gene S.

A downside to the bellows shaft seal is that PYI recommends replacing the bellows at six year intervals. Replacement requires a haul-out whereas a conventional shaft log can be serviced in the water. A catastrophic failure of the bellows underway is a big problem that would not be fixed without a big mess and a spare bellows. Some sailors worry about the failure of the bellows with the boat unattended. I can't see this as a problem without a fire or something else that would be quite a disaster itself...

I have had excellent service from a first generation (no vent) PSS for over 15 years. I have replaced the bellows just once as recommended and keep the old one as a spare. The old one seems as good as the day I received it.

If you worry about a plastic bellows being the only thing between the ocean and your boat- it is not a problem unless something else causes the failure like a broken engine mount or shaft flange. I have had a catastrophic running gear hit that bent the propellor shaft strut and bronze shaft like a pretzel and the PSS shaft seal remained water tight until I could get the boat hauled...

For that- I'll stand behind the PSS seal!

Add your comment: