PSS shaft seal and engine movement

[John Langford]

In the course of adjusting my throttle cable to allow my Universal M35BC to produce full power, a strange thing happened. As I pushed the engine under load AT THE DOCK up to 2500rpm, the top of the recommended cruising range, my shaft seal began to spray salt water. I have used PSS shaft seals for many years and this had never happened before at any power level up to 2500rpm.

My first thought was engine alignment but I checked it out and it was fine. Then I tightened up on the bellows by about 1/4" and the problem went away. But then I wondered if the culprit was putting the boat under heavy load at the dock. My question is: when powering up at the dock, will the engine surge further forward on its mounts than it would underway? And could it do so enough to cause the shaft seal interface to become so loose it would begin to leak? Any views on this?

[Noah]

Caveat: I am no mechanic. But, I do not think so. I run my engine at the dock, straining on the lines, at 2000+ RPM monthly in both forward and reverse—to get it up to temp, as I don't usually do long motor voyages. No probs. Albeit mine is an 25XP, standard stuffing box and Bullflex coupling. Been worried about the dock cleats, however..

[Jim Hardesty]

when powering up at the dock, will the engine surge further forward on its mounts than it would underway?

My thinking is that it wouldn't surge/move any further forward, BUT, it would surge/move for a longer time.  Reasoning is that tied up the strain is steady.  When in open water the max force would be at acceleration then reduce at steady speed.  A little off topic.  I've wondered about how much the alignment changes from a stopped engine to a running engine pushing the boat.  Being a machinist at one time I've gone below when motoring and checked the shaft rotating and there doesn't appear to be much runout.  FWIW Shamrock had 500 engine hours when purchased and a worn cutless bearing that I changed and aligned engine now at 1300 hours the cutless bearing is still tight.  Shaft seal only leeks enough to keep a sponge below the seal wet.
Jim

[John Langford]

Thanks for comments so far. Looking over my post I note that it wasn't clear about the question which is: would the engine move forward on its mounts MORE at the dock than when underway. This matters only if you have a shaft seal because the stainless steel donut fitting on the shaft would move forward with the engine thereby reducing the tightness of the connection between the graphite face and the donut.

In my case, I am virtually certain this was the case since the shaft seal sprayed water at the dock but has never done so underway. The explanation might be that the engine places more forward stress on the mounts at the dock because the pressure of the prop pushing the boat forward is not offset by the boat actually moving forward.

[Roc]

John,
There could have been some debris between the carbon and SS surfaces.  That will not give good contact.  Burping it would clear that up.

[John Langford]

I did burp it and it also burped itself by spraying water everywhere😬😬😬

[Roc]

Hi John
PYI also told me if burping didn't clear any debris, you can use fine sandpaper, 400-600 grit.  What I do is fold it in half and place it between the carbon ring and ss rotor.  Spin the shaft so the rotor spins against the sandpaper.  this cleans the rotor surface.  Then move the sandpaper around to clean the stationary carbon ring. 

[Robert Mann]

If the boat is tethered to the mooring lines the thrust from the prop has to go somewhere, instead of moving the boat forward.  I believe the only place the thrust can go, working on Newtons law of equal and opposite reactions, is straight through the engine mounts (plus wasting some in water shearing), thus relieving the pressure on the PSS spring.  Another point to watch is that there is a good chance the engine temperature will rise if you are just beating water in the slip with the propeller, so make sure you watch the temp gauge and make sure the overheat alarm is functioning. Another point to watch is; if you run astern with the boat tethered, water will be forced up the stern tube by the prop and then break the seal of the PSS.  Yes, I have managed all 3 of the above conditions at different times.

[John Langford]

Since the graphite/S donut surface is clean, I have had no water spray for several years of normal operation, and the spraying only occurred when I pushed the revs up to 2500 and above when the boat was tied to the dock, I am satisfied that the problem was the engine surging forward on its mounts, causing slack in the bellows and thus leakage. My advice: pay close attention to the shaft seal if running the engine under substantial load at the dock. Thanks everyone for the contributions.

[Dale Stone]

Hi,
Thinking the bearing hadn't enough water for cooling and lubrication during the dock exercise. Do have the vented type?

[John Langford]

The interface was very cool with lots of 50 degrees F salt water spraying out of it at high revs. 😬😬😬

[Dale Stone]

Then had to be something got between the graphite and the SS rotor to create the leak. Hope it doesn't happen again.

[Dark n Stormy]

I had my PSS walk/come loose while underway and do the water fountain for me.  The set screws must have gotten loose enough to cause the forward ring to slide forward toward the engine.  the front ring stopped at the clamp/flange that holds propeller shaft.  In a panic all I could see to do was move the rubber bellows forward on the log to give more tension on the matting surfaces. All seems fine now but I can imagine if the rubber bellows becomes old and hardened and doesn't push hard on the mating rings water could come through.   

I also imagine going in reverse the prop wash/thrust could add pressurized water to the matting surfaces and cause the spray.

A little disconcerting for me to think that there is no real mechanical divider between outside and inside other the spring pressure of the bellows boot.

[Stu Jackson]

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A little disconcerting for me to think that there is no real mechanical divider between outside and inside other the spring pressure of the bellows boot.

d&s:  Very good description of one of the options available for connecting the stern tube and the engine coupling.

It appears that one potential and temporary solution to what you describe here is what I've come to realize is a basic and necessary "tool" on our boat:  RAGS.

Like duct tape (and a square bit screwdriver here in Canada!:D) we've found many uses for these RAGS, well beyond the simple "wipe that spill up" stuff.   

Danged moving parts.  Always sumpin', ain't it?   

[Rortega46]

Since we're on the subject, the set screws on my PSS dripless shaft seal loosened last Sunday and the SS rotor/retention collar slid forward. With the engine running at cruising speed water was pumping in faster than a garden hose.  Water quickly overflowed the bilge.  Luckily I was near the shipyard and the owner made a boat call to explain how to adjust and secure the collar.  Lesson learned and crisis averted!  My annual maintenance routine now includes checking the tightness of the set screws on the PSS shaft seal.