How to install your PSS dripless shaft seal
The PSS Type A is a mechanical face seal: a 316L stainless rotor clamps to your propeller shaft and spins against a stationary carbon flange, while a moulded Nitrile bellows fits over the stern tube and is held with two hose clamps. The bellows pre-load keeps the faces together and compensates for propeller thrust, misalignment and vibration — giving you a completely dripless stern gland with no packing and far less maintenance than a traditional stuffing box.
Fitting one is straightforward for an experienced boat owner, but it must be done correctly: the pre-load and the order of assembly are what keep your boat dry. Read the whole guide before you start, and follow the steps in order.
Before you begin — safety first
- The boat must be out of the water for the entire installation.
- Never use oil, grease or any petroleum product, and never use silicone on any part of the seal. They damage the Nitrile bellows and the carbon face. Use clean soapy water (soap and water) as the only lubricant.
- Work in a clean area and keep all components free of grit, swarf and contamination.
- If you are at all unsure, have the seal fitted by a qualified marine installer.
Fitting it step by step
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1
Prepare the shaft
Lightly polish the propeller shaft with #400–600 sandpaper so the components slide on smoothly. Sand over the keyway to remove any burrs or sharp edges that could nick the o-rings as parts pass over it.
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2
Fit the bellows & carbon flange
Slide the Nitrile bellows with the carbon flange onto the shaft and over the stern tube (shaft log). Secure the bellows to the stern tube with the two hose clamps provided. Lubricate with soapy water only to ease it on.
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3
Fit the stainless rotor
Confirm the rotor's two o-rings are seated in their grooves, then slide the rotor onto the shaft (soapy water only). Apply blue thread-lock to the set screws and snug them — final tightening comes after you set the pre-load.
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4
Reattach the coupling
Reconnect the shaft coupling and check the engine/shaft alignment. The seal compensates for minor misalignment and vibration, but the driveline should still be correctly aligned before you set the bellows pre-load.
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5
Set the bellows pre-load
Slide the rotor towards the carbon flange to compress the bellows by the correct amount for your shaft size (see the chart below), keeping the faces square. This pre-load is what holds the faces together and keeps the gland dripless.
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6
Lock the set screws
With the pre-load set, tighten the set screws to the torque for your shaft size — see the chart — then fit and tighten the locking set screws on top to stop the rotor moving on the shaft.
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7
Connect venting / water feed
Fit the vent or water feed to suit your boat's speed (see the venting notes below). This keeps water at the seal faces and lets any trapped air escape so the faces stay lubricated.
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8
Launch & check
On relaunch, check the seal at the faces for any weeping and confirm the vent is working. Thereafter, inspect the bellows regularly and plan to replace it about every 6 years using the PSS Maintenance Kit.
Bellows compression (pre-load) & torque
Set the correct pre-load for your propeller shaft diameter, then torque the set screws to the figure shown. Getting this right is the single most important step in the installation.
| Propeller shaft diameter | Compress bellows by | Set-screw torque |
|---|---|---|
| 3/4" to 1-3/8" | 3/4" (20 mm) | 6 ft-lb |
| 1-1/2" to 3-3/4" | 1" (25 mm) | 8 ft-lb |
Measure the compression carefully and keep the rotor square to the flange. After torquing the set screws, always fit the locking set screws on top.
Venting & water feed
The seal faces need water between them. How you supply it depends on how fast your boat runs.
Low-speed boats
Fit a 3/8" vent hose run to at least 2 feet above the waterline, with no loops that could form a siphon. This lets the seal self-vent and keeps water at the faces.
High-speed boats (over 12 knots)
Supply a positive (pressurised) water feed to the seal, with a maximum of 10 PSI. Pressurised feed ensures the faces stay flooded at speed where a simple vent may not keep up.
Twin-engine installs
On twin-engine boats, plumb a crossover between the two seals' water feeds so both stay supplied even if one engine is not running.
Operating limits
Temperature −15°C to 107°C, pressure 10 PSI (0.68 BAR), up to 10,000 RPM, for shafts 3/4" to 3-3/4" (20 mm to 95 mm).
This page is a guide, not a substitute for the manufacturer's instructions. Always download and follow the official PSS installation instructions for your seal: PSS installation instructions (shaftseal.com). If you are unsure at any stage, use a qualified marine installer.
Questions before you fit it?
Our team has been supplying quality marine products since 1963. If you want to double-check a size, the pre-load or the venting for your boat, give us a call — we are happy to help.
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