Lately the prop shaft connection at the stuffing box on my boat has been dripping constantly, so I tightened it some. However, I must have over-tightened it because now it doesn't leak at all now. Can you tell me the rule of thumb for how often this should leak?
Mark Matthews responds:
Due to the difficulty reaching them and the mysteries that often surround their care, stuffing boxes are often neglected for years. However, in general, the packing inside them should be changed every other year.
Now, regarding your leak. For starters, remember that a stuffing box is designed to leak. When the engine is in gear and the shaft is turning, two or three drops a minute is all it takes to keep the shaft lubricated. Any more than this and the nut should be tightened down to compress the packing.
Take care not to tighten the packing nut too much. You’ll want to tighten the nut no more than a quarter of a turn at a time. When the packing gland stops dripping, it’s tight enough. After you do that, run the engine for a minute and then feel the stuffing box with your hand. You don’t want to feel any significant heat. A little warmth is OK initially until the packing seats itself, but take care because serious heat can score and damage the shaft. If the leak persists, it's almost certain that the packing needs to be replaced. This can be done while the boat is in the water, but make sure your bilge pumps (and nerves) are up for the task where a prodigious amount of water may momentarily be flowing into your boat.
Work quickly with a packing removal tool to get the old packing out. It must all be removed in order for the new packing to go in or otherwise the leak will persist. Once the old packing is out, install five or six rings of new packing. Cut a diagonal slit in the each ring to allow it to meet up with itself. Stagger the joints about 120 degrees from each other. Put the packing nut back in, tighten it, and then wipe the sweat from your brow and grab a cool one. You'll have deserved it.