Leakage is necessary to cool the stuffing box and reduce the wear. There are three conditions that will shorten the life of any packing gland. The first is excessive heat, usually caused by over tightening the gland nut. To control heat generated by the friction between the shaft and the packing gland, a small amount of leakage provides lubrication and cools the packing gland. Now for the answer to the how-many-drops question. The best way to ensure you have enough water leaking through the gland, is to place the back of your hand against the stuffing box while the shaft is turning. If the temperature is uncomfortable, it means it is too hot. Loosen the gland nut to increase leakage until the stuffing box is comfortable to the touch.
The second condition that will shorten the life of your packing material is a sideways movement while the shaft is spinning. If you observe a wobbling motion, measure the amount by clamping an object, like a screw driver, so that the tip is touching the shaft. Spin the shaft and measure the gap. If it exceeds .003 of an inch, you probably have a misaligned engine, warped shaft or a worn thrust bushing. The sideways motion of the shaft will cause excess wear of the gland and will allow water to pass freely through the gland.
The packing gland will need replacement when your feet get wet upon entering the gangway or you no longer can control the flow of water leaking past the gland by tightening the stuffing box nut. Hopefully it's the latter you deal with first. Never add new packing material to old. The old packing gland material will lose its lubrication over a period of time. Dirt and grit may also be present, causing rapid wear to your shaft. Replacement of a propeller shaft costs well over $200.00 verses packing gland material costing approximately $3.00.
It is preferable to replace the packing material when your vessel is out of the water, but if you can no longer control the leakage and don't want to haul your boat out, you can stop the water from entering by putting Play-Doh or putty into some kitchen plastic wrap and rolling it into a cigar shape. Dive under the boat and jam the plastic plug around the shaft, forcing it up the shaft tube. This will slow the leakage while you replace the packing. Don't forget to remove the plastic plug, without water for lubrication the new packing material will burn up.
Some of the older stuffing box assemblies have a locking nut to lock the gland nut in place. Corrosion and salt-water build-up will sometimes seize the lock nut to the gland nut. Use a generous amount of penetrating oil and wait a few minutes for the oil to penetrate deep into the threads. With a hammer, tap lightly around the stuffing box to loosen up the corrosion. The newer stuffing box assemblies have a gland nut and a gland follower. They also might need penetrating oil to help in removal. Once removed, clean all threads and parts with a wire brush to remove corrosion and water build-up. Do not wire brush the shaft; use fine 320-grit sandpaper to clean the shaft surface. Remove the old packing materiel with a packing extractor. Make sure you have removed all of the old packing material. A bent coat hanger can also be used as a packing extractor.
severe damage can occur to the shaft and stuffing box if you wrap the packing
around and around without cutting individual rings.
Wrap the new packing around a clean section of the shaft before cutting, making sure there are no twists as you wrap. If you don't have enough room to work on the shaft, use a wooden dowel the same size as your shaft, and cut the rings on the dowel.
Cut the rings from the spiral wrap at a 45-degree angle. The rings should completely circle the shaft, leaving no gaps between cut ends. Cut and replace the same amount of rings as you removed. Apply a small amount of waterproof grease to the shaft. This will prevent wear and excessive heating until the water can reach the packing to provide cooling and lubrication. Place each ring on the shaft, pushing them into the stuffing box. Stagger them at a 90-degree angle to the preceding ring. Use a lightweight oil or an antiseize compound on the gland nut before replacing. This will help for future adjustments and removal. Tighten the gland nut until the follower squeezes all the rings together, being sure not to over tighten. Follow the directions given above on how tight the gland nut should be.
Don't forget to remove the plastic plug from the shaft, before starting your engine.
Tools, Hardware and Supplies
Small inspection mirror
Small wire brush
Packing material impregnated with graphite lubricant
Light oil (SAE 10 weight) or antiseize compound
Penetrating oil (WD-40)