Stuffing Box Maintenance

Another frequent discussion topic on the Aloha Discussion List is adjustment or re-packing of prop shaft “stuffing boxes” (aka “packing glands” or “propshaft glands”) so we have tried to summarise the most common questions and advice in a single article here.

Q. Which way do the nuts turn?
A. Just in case this varies from one unit to another check by looking at the exposed threads, and don’t exert too much force, until you’re sure you are turning it the right way. As far as we are aware (and please tell us if you know different) the stuffing boxes all have a standard thread. This means that looking towards the rear of the boat (i.e. from in front of the stuffing box with the compression nut nearest to you), the locking nut undoes clockwise and does up counter-clockwise. The compression nut gets slacker or is removed counter-clockwise and is tightened clockwise.

Q. What is the packing?
A. Packing comes either as “traditional” greased or waxed flax, or a more modern Teflon impregnated packing. It is available either ready-cut into pre-sized rings of various sizes to suit different boxes, or as continuous square sided rope also in various thicknesses to match the clearance between shaft and stuffing box body. Alohas usually require 1/4inch packing.

Q. At what rate should a properly adjusted stuffing box leak?
A. This depends on the type of packing used. With the greased flax packing the stuffing box should not drip when the shaft is stationary, and should leak 2 or 3 drops a minute when turning. The Teflon impregnated packing is usually drip free.

Q. How else should I check that it is adjusted correctly?
A. It is vital that the stuffing box does not overheat, since this will cause scoring damage to the shaft. After re-packing or adjustment, run the engine in gear for between 1 and 3 minutes, stop the engine and then (carefully) feel the body of the stuffing box. If it is hot to the touch it is too tight. Slacken the compression nut and re-test until the drip rate and temperature are correct.

Q. I can’t stop it dripping too fast no matter how I adjust it or when I do, it gets too hot ­ what next?
A. It’s time to re-pack the unit.

Q. Can the packing be replaced without removing the shaft?
A. This depends on accessibility and clearance. Provided there is room between the shaft coupling and the stuffing box for the compression nut/spacer to be undone and slide far enough away from the stuffing box to allow the existing stuffing to be removed, it can be achieved with the shaft in place. Note, however, that if you want to check or replace the flexible hose and clips that are used to mount the stuffing box, the shaft must be removed. If the boat is already out of the water this is probably the best option, and allows the cutless bearing to be checked/replaced at the same time.

Q. Can the packing be replaced with the boat in the water?
A. Provided the shaft doesn¹t have to be removed this should be possible. Some water will leak in whilst you do this, but Alohas usually have quite a tight fitting stern gland at the outer end of the prop shaft so the flow is quite limited. Nevertheless, speed is still important so make sure you have all the required materials and tools prepared and to hand before you start.

Q. What is the procedure for replacing the packing?
The steps are:

  • Before starting to dismantle, have four rings of the right size ready to insert. If cutting these from continuous rope, wrap this around the exposed shaft (or other circular tube of the same diameter such as the right sized socket spanner) five or six times and then cut across the windings at an angle with a sharp knife.
  • slacken the lock nut
  • undo the compression nut and slide this and the compression spacer up the shaft towards the shaft coupling
  • remove all of the existing packing. Any packing left behind will reduce the chances of the new packing sealing properly. This task will be made easier with a proper tool that looks a bit like a corkscrew on a flexible shaft, but this isn¹t essential and bent wire and pliers can also be used.
  • Insert the new packing, making sure the joint in each ring is offset from that in the previous ring. If your box has a metal greasing spacer it should be fitted between the second and third rings.
  • Re-fit the compression spacer and compression nut.
  • If your fitting has a grease fitting apply a couple of shots or turn the cup down a couple of turns.
  • Do the compression nut up hand tight plus about a quarter turn more. Secure with the locking nut.
  • Now run the engine for 1 to 3 minutes in gear and check for drip rate (not if Teflon packing is used) and temperature. Adjust as needed, and then run for rather longer and check that it is still only warm not hot.
  • Over the next few uses check for drip rate and temperature.

Q. Should the stuffing box be greased?
A. Some stuffing boxes have no grease fittings and rely on the greased packing and grease applied during assembly for lubrication. Others are fitted with a grease nipple, screw-down greasing cup or remote greaser, and in some cases have a metal spacing ring between the packing rings to aid grease distribution. In any event, this seems to suggest that occasional greasing is a good idea. If you have the greasing cup, a half or full turn, or until resistance is felt, each time you use the engine works well.

Q. Should the transmission be left in gear or in neutral when sailing?
A. A stationary propeller may cause more drag than one that is able to “idle” (although opinions on this vary). However, an idling shaft can be a significant source of noise and vibration, as well as creating wear on transmission bearings, seals, couplings and the stuffing box itself, and allowing the stuffing box to drip. The manual for the Hurst transmission fitted to many Alohas specifically instructs that it should be placed in reverse gear when sailing.

Q. What else can cause problems with the stuffing box?
A. Nigel Calder makes the point in his book that poor engine installation or alignment may manifest itself as (recurring) problems with the stuffing box.

Q. Is there an alternative to the stuffing box?
A. Several owners have fitted instead a PSS (Packless Sealing System) Shaft Seal from PYI Inc. This does not drip, and requires little or no maintenance or adjustment, but the risk of “catastrophic failure” may be slightly higher.

Written by Liam Fitzgerald