Tuesday, April 22, 2008

Propeller Shaft Mechanical Seal Replacement

This article will cover the replacement of a Propeller Shaft Mechanical Seal for the Robertson & Caine 45' Leopard (4500) catamaran, equipped with Janmar 50hp motors, Kanzaki KM4A direct drive transmissions, and a 30mm stainless steel drive shaft.

NOTE: The actions detailed in this article are specific to the Leopard and may not be possible on other makes or models. Many other vessels require significantly more effort or tools to disconnect the drive shaft, and in some cases this may only be possible with the boat out of the water. Check your owners manual and examine the working space and mechanical connections before going further.

Some history: Many boats built before the 1990's used packing gland/stuffing box type seals around the propeller shaft where it exited the aft end of the boat. These were invented hundreds of years ago, and have worked reasonably well for most boats (there wasn't really any alternative anyway), provided they were installed correctly, they were scrupulously maintained, and when they failed, you noticed it in time.

But they had problems. They worked by allowing a small amount of the surrounding salt water to leak pass the shaft and into the boat. This both cooled and lubricated the shaft as it spun, but slowly filled your bilge with saltwater. If the packing gland (the material used as the seal) were to get to hot, it could burn up, creating a significant leak that if unnoticed could result in the loss of the boat.

Recent material sciences have devised better packing gland material that doesn't require constant salt water cooling, and for many folks this solution seems to work just fine. This is made of a Teflon material, and often referred to as "dripless" packing gland. If you have an older boat, with a stuffing box and packing gland, you might consider upgrading to this new material. Many of the cruisers I've met use it, and seem to like it a lot, but I can't speak for them.

That was then, this is now.

A few decades ago, engineers devised a better system, which is called, generally, a "dripless" mechanical seal [not to be confused with the "dripless packing gland"]. Instead of creating a seal running along the shaft itself, they added a stainless steel collar (called a rotor) to the shaft and created a rubber bellow with a graphite "facing" at one end that is pressed up against the collar, creating the seal between the forward end of the graphite facing and the aft end of the collar. Since the rubber bellow is compressed a bit, it continually pushes the graphite facing against the collar, maintaining a seal even when the engine or shaft itself vibrates.

NOTE: It is possible, after installation, to manually compress the bellow even further, allowing some water to escape into the boat. This is normal, but one should take care to insure that the seal mechanism is free of any other component and that nothing will interfere with its normal operation. Obviously, any boat should have adequate bilge pumps and flood alarms as well.

There are a few manufacturers of mechanical seals, but we used the PSS seal from PYI Inc. The kit cost about $300.00 for the size necessary for our boat. Their sales force was excellent, patient and very, very helpful [I was stranded in Mexico at the time and AnnMarie was dealing with them over the phone, not sure what she was ordering or how it should be], and while repairing the port shaft seal, we discovered that the set screws were missing out of the package Ann shipped me (not their fault but ours), they shipped another set next day air, and threw in some more as well when we purchased the seal for the second starboard drive shaft. Good guys all around!

We should be able to expect these seals to last between seven and ten years without any regular maintenance beyond occasional inspections. And, there shouldn't be any water leaking into the boat, which means a dry, saltwater free bilge, which means a happy boat owner. From my perspective, that alone is worth the price of admission, but the peace of mind knowing that there isn't much that can go wrong, and if it does, I can fix it, or get great help from the manufacturer, is all bonus.
The Parts of the PSS Shaft Seal
1. Propeller Shaft
2. Shaft Log (Stern Tube)
3. Stainless Steel Hose Clamps (4)
4. Bellow (1)
5. Carbon Graphite Flange (1)
6. Stainless Steel Rotor (1)
7. Stainless Steel Screws
(5 total/4 for Rotor, 1 spare)

8. Nitrile O-Rings (2 in Rotor/2 spare)
9. Nylon Hose Barb Fitting

When we bought the boat both shaft seals were this type of mechanical seal (see photo below), but made by Volvo. What is different about the Volvo mechanical seal is that there was no mechanism to bleed off any air that might collect inside the rubber boot. This meant that whenever you hauled the boat, you needed to "burp" the rubber bellow, to remove any air trapped inside. Not doing this would prevent the collar/seal from being properly cooled and lubricated, and eventually burn out the seal.

This might have been a contributing factor when we hauled the boat for inspection, or when we hauled it for storage in Trinidad. In both instances, I do not specifically recall anyone taking this action, and I was unaware it was necessary at the time. As it was, the seals worked without problems for at least six years, and only began showing signs of wear into their seventh and eighth year of use. That is well within the manufacturer's warranty period so even if they had been properly treated by the yard personnel both times the boat was out of water, I would still be satisfied with it's performance. That said, I'd not recommend this particular type of mechanical seal, as I believe the newer versions are superior. The picture below depicts the components of the new kit.

The new seals (see photo above) have a vent tube that allows air to automatically vent out of the shaft area, minimizing the likelihood of air being trapped within the bellow. The white barbed nipple protruding from the black rubber bellow is connected to a hose that is led high above the water line. This prevents air pockets from forming inside the bellow and means the rotor and graphite facing are always properly cooled and lubricated. The kit does not include the bleeder line hose or clamps for it, you will need to supply these yourself, as well as a means of attaching the hose to a bulkhead.

Note: On non-heeling catamarans, this hose need only be run a foot or so above the waterline. On monohulls, or any vessel where significant heel angles can be expected, it must be run high enough that the end of the hose is guaranteed to always be above the waterline, regardless of how far over the boat is heeled, or a dangerous siphoning condition could occur.

WARNING: Follow all of the manufacturer's instructions when installing the shaft seal. Where there are discrepancies between my steps and those of the manufacturer, default to their instructions. The information contained on this website is not intended as a substitute for the procedures supplied by the manufacturer, and is only a rough description of the steps I took when replacing my shaft seal.

Do not attempt this when the engine is still hot.
WARNING: Almost every tool and part used in this process will, at some point in the process, fall into the bilge and roll into the puddle of saltwater under your engine. Do not attempt this procedure if you are easily annoyed, have had too much coffee or are under-medicated. Expect to spend a considerable amount of effort finding pieces in areas that are hard to reach. Rushing will only exacerbate this. Use some form of padding while kneeling inside the engine compartment [I use an old neoprene dive suit], and take frequent stretching breaks. Drink plenty of non-alcoholic, rehydrating liquids. If you are in doubt of anything, STOP, THINK & ASK. Maybe even pay a mechanic. Don't break your boat!

To complete this procedure you will need the following items:

1) A torque wrench.
2) A socket driver, and the appropriate socket and hex drive attachment.
3) Large pliers or channel locks.
4) Screw drivers.
5) Allen wrench (supplied with mechanical seal kit)
6) Open ended box wrenches.
7) Monkey wrench.
8) Scissors or knife.

Additionally, you will need a length of marine grade hose that fits over the barbed nipple of the shaft seal and can be permanently fastened to a nearby bulkhead, extending at least one foot (or more) above the water line and some means of attaching it permanently to the bulkhead, at least two small stainless steel hose clamps to secure said hose to the barbed nipple, a larger stainless steel hose clamp that fits around the propeller shaft with minimal excess, some 800 grit emery paper, a wire brush, and at least one lovely assistant.

The first step in replacing the mechanical seal involves disconnecting the shaft from the transmission collar. On many boats, this procedure must be undertaken only when the boat is hauled out, as the only means of granting enough clearance to remove the seal requires removing the propeller shaft completely from the vessel. On the R&C 4500 Leopard, the shaft can be slid back far enough to easily replace the mechanical seal without removing the shaft or exposing the opening to the sea, so it was possible for us to change both seals with the boat in the water.

It is advised that you perform this operation while the boat is hauled out and on blocks in a yard. Take proper precautions when attempting this anywhere other than a yard!

CAUTION: Performing this operation in the water is risky. It could result in the shaft sliding out of the boat, resulting in the loss of the shaft & propeller, as well as the serious risk of sinking that would occur from creating that large an opening in the vessel. Do not attempt this without adequate working bilge pumps, shaft plugs, and a securing line tied to the propeller itself. You might also consider "packing" the outside of the shaft at the cutlass bearing to minimize water entering the vessel. Be prepared for a significant amount of water, and be able to reattach the existing seal should this amount prove more than your bilge pumps can easily handle.

First, place a stainless steel hose clamp on the propeller shaft just aft of the transmission shaft clamping mechanism. It is a round flange that attaches to the transmission with four large through-bolts, with two orthogonal brackets that clamp to the drive shaft using six large hex capscrews, three on each side of the shaft.

Make sure you treat each of the six cap screws in place with a penetrating oil, as these screws tend to be the most exposed to salt water and corrosion. Spray some oil down into the shaft area itself (along the horizontal split in the flange) and on the four through-bolts. Allow all of the them to soak for as long as possible before proceeding. This will actually make a considerable difference in the ease with which the shaft will break free of the transmission bracket. Remove any rust that may have accumulated inside the capscrew hex sockets as well.

Using a torque wrench and a hex driver, loosen the six hex capscrews that clamp the transmission bracket around the drive shaft. Note the amount of foot pounds necessary to break each capscrew, and record this for re-installation. Take care to only break each of the six caps free, before loosening any one screw completely. Once all cap screws have been initially loosened, unscrew all of them and remove them completely. Place each of them in a rust-penetrating solution to soak.

Place the transmission in reverse to lock it in place. Place a wrench (you may need a monkey wrench for this operation) around the hose clamp. The hose clamp's purpose is to protect the shaft from scarring due to the torque forces applied by the teeth. Spin the shaft until it breaks free and spins inside the flange without resistance. The shaft will only spin, it will not slid backwards, away from the transmission at this point, due to a shear pin inside the flange assembly.

Next, remove the four through-bolts and nuts that hold the transmission to the flange. Once free, you should be able to slide the shaft and flange aftwards (you may need to use the hose clamp as a grasping point), exposing the shear pin and washer behind it.

WARNING: Do not allow the drive shaft to slide out of the boat. Keep the hose clamp in place whenever repositioning the drive shaft.
Remove the shear pin and washer from the drive shaft. Slide the shaft far enough aft to create enough room to remove the flange, sliding it forward, off the end of the shaft. Next, slide the shaft as far forward as possible. Reposition the hose clamp to the forward most position of the drive shaft, allowing the removal of the shaft seal. Use the emery paper to remove any burrs or gouges on the shaft seal.

WARNING: Be very careful not to scar the shaft seal when replacing the seal, as this may interfere with the rotor seals later on.

Next, prepare the new shaft seal for installation by attaching a length of hose to the barbed nipple protruding from the mechanical seal.

Place two small hose clamps around the hose. Survey the area and locate an appropriate bulkhead on which to attach the hose. The end of the hose must be placed at least one foot above the water line. Follow the manufacturer's instructions for specific details regarding this procedure.

Disconnect the hose clamps holding the existing shaft seal to the transom log [the shaft log is the fiberglass flange that protrudes into the boat through which the shaft enters] and slide the shaft as far forward along the shaft as possible.

Remove the hose clamp from the shaft and reattach it aft of the old seal. Allow enough room to slide the shaft back far enough to remove the old seal and install the new one.

NOTE: At this point, water will flow into the boat through the shaft log from around the shaft. The amount should be less than what your boat's bilge pumps can easily cope with. If the flow rate is significant, place rags or other stuffing material around the shaft to reduce the flow, but make sure to remove these once you are ready to install the seal.

Loosen the hose clamps on the aft end of the mechanical seal enough that they will easily allow the seal to be installed over the log. Install the new shaft seal, sliding it along the shaft. Slide the shaft further forward, remove the hose clamp from the shaft, and re-attach it to the end of the shaft. Slide the mechanical seal back and force the seal around the shaft log until it covers enough of the log that you can adequately tighten the two rear hose clamps supplied with the seal.

At this point, water will still be flowing into the boat (see picture above) . Make sure the end of the hose is placed above the water line. Slide the shaft forward enough to make room to slide the hose clamp aftwards and re-tighten. Slide the new rotor onto the shaft, carefully following the manufacturer's instructions.

The rotor has two O-rings set into the inside surface of it [the surface which contacts the shaft], which must be correctly placed onto the shaft or the rotor will leak. Do not use grease or oil-based lubricant for this process. The PSS product literature strongly recommends dish washing liquid mixed with water, if needed, to act as a lubricant for this step. Follow the manufacturer's instructions carefully. Reinstall the flange after it, and slide the shaft as far forward as possible.
Using the allen wrench supplied with the kit, install a single set screw into the rotor. Tighten it until it just barely touches the shaft. This single set screw can now be used in lieu of the hose clamp as a means of preventing the shaft from falling out. Be very careful not to cross thread the screw, but be aware that the Locktite coating may make the screw difficult to turn at first.
Remove the hose clamp, using the new rotor to clamp the shaft instead.

Reinstall the flange on the shaft. Insert one capscrew to use
as a means of clamping the flange to the shaft. This also prevents the shaft from sliding out of the boat.

Slide the shaft as far forward as possible, exposing the end enough that you can replace the washer and then the shear pin. Make sure that the washer is placed aft of the shear pin or it will have no effect. The shear pin and washer are what prevent the shaft from sliding out of the boat should the capscrews loosen. Make sure these are correctly installed!

Slide the flange back against the transmission and reconnect the four through-bolts.

Next, slide the rotor up against the graphite surface of the mechanical seal. Use just enough pressure against the seal to prevent the water from entering the boat.

Replace the hose clamp, aligning it against the rotor, just forward of it. This clamp marks the neutral position of the rotor. Slide the rotor aftwards, against the graphite surface, compressing the seal bellow. Use the manufacturer's guidelines to determine how much to compress the bellow, as measured by the distance between the hose clamp and the rotor. In our case, it was 3/4".

Tighten the rotor set screw using the supplied allen wrench. Add another set screw to the alternate screw hole, and tighten it as well. Place the two remaining set screws into each of the screw holes, tightening down onto the existing screws. This locks the innermost set screws in place.

Slide the hose clamp up against the rotor, and re-tighten. This acts as an additional security in keeping the rotor in place.

NOTE: Do not skip this step, as significant leaking can occur if the rotor loosens and slides forward, allowing seawater to escape into the boat. In fact, many people use two hose clamps.

Reinstall the remaining capscrews, and re-tighten and torque to the manufacturer's suggested setting. If you cannot locate this value, make sure they are at least as tight as the highest foot pound setting required to originally break any of them free.

Mount the hose against a bulkhead using permanent straps to hold it in place. Do not allow anything to block the open end of the hose. Make sure that the hose water level is consistent with the water line. Mark this position on the bulkhead wall for future reference.

Place the transmission in neutral, start the engine, and examine for leaks. Have your assistant place the engine in forward and reverse while at idling engine speeds (make sure the boat is adequately anchored to the dock) and look for leaks. Be careful not to go near the spinning shaft, as it can cause extreme injury! Motor the boat around at low speeds for a while, noting the behavior of the shaft seal. You may notice, initially, a fine mist being produced, this is normal and should cease after a reasonable break in period.

With the engine idling and the transmission in neutral, feel the shaft and bearing surfaces to make certain they are not overheating. Check that the hose leading from the seal is not damaged and is properly installed.

Clean all of your tools using solvent and then add a light coating of lubricant or grease to them to prevent corrosion. Make sure the bilge is dry and free of any items that might clog the bilge pumps. Recheck your bilge pumps and alarms.

Recheck everything after 1 hour of normal operation, then again after ten hours, and then again after fifty.

Hopefully, you have installed the seal properly and can reasonably expect another five to ten years of maintenance free operation.