Expert Fingers: How to Install a PSS Shaft Seal

July 24, 2014 - 10:00 AM by Samantha Pudney

When it comes to mechanical seals, there is only one that’s trusted by ship builders and shipyards across the globe: the PSS Shaft Seal. Manufactured by PYI Inc., this seal expertly keeps out water in the bilge and nearly eliminates all maintenance costs.

a shaft seal

While you can hire someone to install your PSS Shaft Seal, you might be able to tackle the process yourself. Follow these step-by-step instructions and you’ll be on your way to properly installing your very own PSS Seal Shaft.

Instructions: How to Install a PSS Shaft Seal

1. Read these instructions all the way through first to be sure you fully understand what is expected of you. Installation is only possible if the boat is out of the water, and the area should be clean.

2. Carefully unbolt the shaft coupling from the transmission coupling and then remove the shaft coupling from the shaft itself. This step may vary in approach depending on what kind of couplings you have.

3. Take the old stuff box and packing material off as well. You will probably see one of three types of packing glands, “Classic,” “Bolt On” and “Thread.” Check with these types to determine how to remove them effectively.

4. Using very fine sand paper, clean the exposed part of the shaft. You should be looking to remove any dirt or rough edges, but be careful around the keyway, which is located at the forward end of the shaft. The stainless steel rotor will pass over this part, and any sharp edges could severely damage the o-rings inside the rotor.

5. Now gently slide the open end of the bellow and its hose clamps down the shaft and settle it on the bare stern tube. Be sure the bellow has a proper fit over the shaft log. You will know it is in place when the bellow overlaps the stern tube by the same amount so the bellow cuff so the hose clamps will be able to tighten the bellow to the shaft log. DO NOT slide the bellow cuff too far down the shaft and over the stern tube. This could damage the inner ribs of the bellow and limit its travel. Finally, tighten the hose clamps to properly secure the stern tube and hit the black clamp protector to the tail of the clamps.

6. Check your carbon flange for any imperfections. Place the carbon flange carefully on the forward end of the bellow and its two hose clamps.

7. Take out the stainless steel rotor and check the two o-rings in the grooves on the inside. The mating face of the rotor shouldn’t have any imperfections either. Take out two of the set screws and screw them into the rotor holes. Don’t worry about the other screws; you’ll use them later. Don’t thread the screws all the way through. You should stop just before the screw protrudes the inside bore of the rotor.

dish soap

Photo by Kristian Ovaska 2004 | CC BY SA

8. Use a water solution or dish soap to lubricate the shaft and o-rings of the rotor. Be sure it’s petroleum free, and do not use any grease, oil or silicone.

9. Now re-attached the shaft couplings back to the shaft and be sure all safety devices given and recommended by the coupling manufacturer have been set in place.

10. Refit the shaft coupling to the transmission by carefully following the manufacturer’s specifications and allowances. Again, check for safety devices and recommendations from the coupling manufacturer and make sure they’re in place.

11. Once the shaft is back in place, make sure the carbon is still centered on the shaft. The carbon ring will be bored at a larger diameter than the shaft, and the bellow cuff must be properly placed on the stem tube. The shaft should also be near the center in the shaft long. Adjust accordingly so the PSS runs true with the shaft. Be sure all of the hose clamps have been tightened around the stern tube and carbon.

12. Slide the rotor down the shaft so that it just touches the carbon. Using tape or a marker makes this “neutral” position on the shaft just in front of the rotor.

13. While sliding the rotor aft, compress the bellow by the amount listed on the bellow compression chart. Use the “neutral” mark as a reference point. While the bellow is still compressed, tighten up those two screws in the rotor against the shaft. You can use an allen wrench for this.

14. Now take out the last of the screws and thread one into each of the holes and tighten them against the first screws. This will lock the first set of screws in place.

15. You will have to plumb the system in order to properly finish this project. How you do this will depend on whether or not your vessel goes above twelve knots. Check with your operations manual.

16. Finally, test the boat. While inspecting the boat, be sure the PSS is working and is in the proper place. There shouldn’t be any water coming in from the PSS seal area. Run everything as you normally would. You will probably see a very fine mist that is spraying from the seal. The PSS requires about an hour of break-in time. After the hour, the mist should be gone.



Even the best mechanic misses a step now and again. If you notice something odd after your installation, check out these three possible problems and their solutions.

A High-pitched Squeal

If you’re hearing this, the PSS might not be getting water. Review your plumbing instructions and see if there’s something you can correct.

Lingering Spray or Mist

If you are still experiencing the mist or spray after the one-hour period, take another look at the bellow compression chart. All of the numbers listed are average figures, but the exact compression amounts might be slightly off depending on the engine mount and the water pressure against the seal. If the compression is off, try adding 1/4″ of additional compression to the seal. The mist should disappear so keep adjusting until it stops.

Dripping While at Rest

If you notice the PSS seal is dripping while at rest, then foreign materials are on the face of the seal between the rotor and the flange. To clean it, slide a clean rag between the two faces. If the boat is sitting in the water, some water will probably come in. That’s okay. Continue to work the rag around the seal and the water will flush out any impurities. The leak should stop after you take away the rag.