Stern Tube and Stuffing Box Check and Repack
or "To Drip or Not To Drip? "
How to kill a Stuffing Box:
- Poor alignment
- Overtightening until the threads strip
- Poor bonding or letting zincs go too long
Stern tube –
Make sure this is straight – an easy indicator that there’s a problem is if it’s worn on the inside from the shaft rubbing against it. We rarely have to replace a whole stern tube, but it’s been done. If there’s wear inside, try getting your alignment right before you start hacking up fiberglass. The shaft should not touch the stern tube anywhere once everything’s in place. If it does, you need to fix it or it will slowly wear a hole in your boat.
Stuffing box –
There are countless variations on the stuffing box, but 2 types are most common. First we will look at the traditional stuffing box. The most common problem is that the packing needs to be changed or adjusted.
You can keep tightening these things down to stop water for a while, but if you keep it up the shaft can get badly worn, and you will never get a proper seal. A proper seal is defined as follows: No water is coming in when the shaft is at rest, and a consistent drip is visible when the shaft is turning.
You CAN change packing in the water but it gets a bit exciting. Water will be pouring in your boat the whole time, and this is not an easy or quick task. Also, once you’ve started picking it apart, you have to finish or you won’t have a seal and you can’t run the engine without damaging it. The nut needs to be backed off completely and slid up the shaft (at which point the boat is filling slowly with water) enough that you can use a dentist’s hook, corkscrew, or similar tool to pick out all the old packing. Then push in new packing, and screw it all back together until it stops dripping. It is much easier and less hazardous to do this hauled out. Follow above procedure minus the boat filling up with water part. Always replace the stuffing hose and hose clamps. It’s cheap and they wear out after a while, and your boat sinks if it tears so why wouldn't you fix it? Get the real stuffing hose, only use regular wire-reinforced exhaust hose in an emergency. 4 hose clamps always (2 at each end) or 2 T-bar hose clamps.
The other type of stuffing box is the PSS Dripless Shaft Seal. Your best bet on these is to keep them clean and free of debris. They really are supposed to be dripless, so if they're dripping something's wrong. Be careful of the ones that have a small water tube coming into them - usually only needed for boats faster than 10 knots. The little tube if broken or cracked will continue leaking water into your boat until repaired - it's a known weak point below the waterline. On many cruising sailboats it can be replaced by a tiny plastic plug. Very rarely the stainless collar on a PSS will get electrolysis and end up with a poor seal, in this case reverse the collar so the smooth side is facing the seal or replace the whole thing.
There are other types of seals, dripless and otherwise, but they are beyond the scope of this article, as they are rarely found on older boats and most current production boats.
Next we will look at the coupler, coupling, and drive saver
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