Cutlass bearing scoring - how much is too much?

[DDW]

The prop shaft was difficult to turn by hand on this boat when I bought it. It is an AT 34 with two cutlass bearings, one about 6' forward of the usual location. The front one was tight, and after some struggles I got the shaft and bearing out. It appears that there is no or insufficient water supply to the Tides seal and forward bearing, seal was fine but there is a lot of silt in the prop tube and on the shaft. Where the forward cutlass runs, the shaft is scored. It looks pretty bad, but with calipers the worst of it is about 0.005 deep (0.010 diameter loss). There are also some crescent shaped pits randomly distributed in the same area.

How bad is too bad before I $pend lot$ of money on a new $haft?

 

[O C Diver]

I've seen far worse still being used. Remember the shaft is designed to handle full RPM / HP plus a significant safety factor. If you run your engine on the pin all the time, I might carry it to a prop and shaft shop for an opinion. If you don't exceed 80% of full load, I think you will be fine.

Ted

 

[stubones99]

A good machine shop can probably add metal to the shaft cheaper than buying a new shaft. It all depends on the boat and HP requirements. Make sure the shaft is trued before re-installing, regardless.

 

[koliver]

I saw mine when the new cutless were put in. Yours is in better shape than mine, and my mechanic weighed in that mine were good to keep using without concern.
I never run on the pin. 8 knots, 2000 rpm (1000 at the shaft) and there is lots of lube water getting to my cutless.

 

[DDW]

I'm kinda thinking I should just put it together and run it. When I put the new cutlass bearing on there is no noticeable difference in clearance between the unworn shaft and the scored area. The old front cutlass (which was quite tight on the shaft) shows no imprint of the scoring, so they seem not to care. The shaft seems to be sized for the max HP with a good margin, and I normally run at 1/3 max power.

 

[TowLou]

At least put a 3m pad to it and clean up the metal I would do to get it shiny again. Even chrome shops should be able to smooth out the grooves. That's what we did for all the piston rods when they got scoured when repacking the seals.

 

[Island Cessna]

I’d polish it with crocus cloth (very fine emery cloth with jewelers rouge as the abrasive) put it back together. As others have said the concern would not be the strength of the shaft, but the roughness of the surface cutting the cutless bearing.

 

[FF]

You are hardly the first with this problem, here is an easy solution.

Shaft Saver

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Manufacturers of Bearings, Cutless Bearing, Elastomer, Fluid Lubricated, Irrigation, Plastic, Pump, Marine, Rubber, turbine, Vertical, Water, Viton,nitrile, EPDM, ...

 

[Portage_Bay]

If you want to spend the $$ the by all means make it perfect. If it were my boat I'd clean it up and put it back in. There are many work boats out there running around with worse wear than that. Putting more hours on in one week than many recreational boats do in a season.

Do check the clearance between shaft and cutlass, you may need a new cutlass.

 

[DDW]

Shaftsaver not going to work in this application, as the worn area has to go past the first cutlass bearing to install. I guess I could put on two of them. The old cutlass was extremely tight (could not turn the prop by hand), not sure how long it had been this way, and yet shows no imprint at all from the scoring. It isn't rough, quite smooth actually, just has some smooth grooves.

 

[kchace]

That is minimal wear of a shaft that has some hours on it. It shouldn't be a problem at all to keep using that shaft as is.

Ken

 

[O C Diver]

Shaftsaver not going to work in this application, as the worn area has to go past the first cutlass bearing to install. I guess I could put on two of them. The old cutlass was extremely tight (could not turn the prop by hand), not sure how long it had been this way, and yet shows no imprint at all from the scoring. It isn't rough, quite smooth actually, just has some smooth grooves.

If the cutlass bearings were that tight, you may need to check the alignment from the engine through the last strut.

Ted

 

[sunchaser]

If the cutlass bearings were that tight, you may need to check the alignment from the engine through the last strut.
Ted

Precisely. Without knowing and fixing the reason for shaft scoring it will only get worse. Shafts do fail.

 

[FF]

"Without knowing and fixing the reason for shaft scoring it will only get worse. Shafts do fail."


Some shaft erosion comes from operating in shallow water where sand is kicked up by another boat and enters the cutlass bearing.

 

[Lepke]

If you're getting adequate water lubrication the shaft should look polished. Nothing more. There should never be silt packed into the bearing valleys. I have 76 year old monel shafts with thousands of hours and 4 bearings per shaft. You probably have an alignment problem. Many yards do a poor alignment job. Learn to do it your self or pay for the alignment and then the repairs. Or at least check it.

Boats with bearings close to the shaft seal usually have some of their engine exhaust water piped into the shaft tube to ensure lubrication. Mine do. In metal boats some people weld a small scoop to the hull and piped to the bearing so forward motion provides the water flow.


Pic is my tail shafts at about 70 years old. Line is in the middle of the bearing surface.

 

[AKDoug]

Mine was worse than that, alignment issues, and the shop said they recommend replacement or repair at .060. They don't repair small diameter shafts like mine.

 

[DDW]

Shaft alignment was originally suspected, but it was pretty much right on. The cutlass bearing has simply swollen up and gotten tight. When the transmission coupler was unbolted, there was no difference, still very hard to turn. With the shaft and cutlass removed, it will not slide onto the shaft easily and cannot be turned by hand. Cause unknown. The aft cutlass is also slightly tight, but can be turned. The new ones slide on with about 0.005 clearance, per spec. The old cutlass has no impression of the scoring, and is not worn more on one side than another.

The setup has a raw water supply piped from the engine raw water pump, through the transmission cooler. This is required for the Tides lip seal. Obviously this needs to be checked for flow. The silt or other deposits on the shaft indicate low or no flow. The boat has been operated on a fresh water lake for the last 9 years, not particularly shallow.

 

[bglad]

The swelled bearing may have been impinging the water grooves restricting flow through the log. The new bearing will likely flow much better. Careful with the water flow since too much pressure may push out your seal although that is very unlikely.

How about running the engine on the hard to check the water flow? You would not have to turn the shaft just run the engine and see how the discharge looks at the stern tube outlet.

Shaft alignment was originally suspected, but it was pretty much right on. The cutlass bearing has simply swollen up and gotten tight. When the transmission coupler was unbolted, there was no difference, still very hard to turn. With the shaft and cutlass removed, it will not slide onto the shaft easily and cannot be turned by hand. Cause unknown. The aft cutlass is also slightly tight, but can be turned. The new ones slide on with about 0.005 clearance, per spec. The old cutlass has no impression of the scoring, and is not worn more on one side than another.

The setup has a raw water supply piped from the engine raw water pump, through the transmission cooler. This is required for the Tides lip seal. Obviously this needs to be checked for flow. The silt or other deposits on the shaft indicate low or no flow. The boat has been operated on a fresh water lake for the last 9 years, not particularly shallow.

 

[DDW]

I do plan to run the engine on the hard, should be easy to do as there is a fresh water flush facility. Neither the engine nor the transmission was overheating (temperature of both is monitored), but there may be a restriction in the transmission cooler from which the shaft water is sourced.

 

[O C Diver]

Before you put the shaft in, disconnect the hose from the engine water source and blow through it. If you can't blow through it, water is going through it.

Ted

 

[motion30]

We're just start the motor with the hose disconnected and see if you have water flow

 

[charles]

prop shaft repair

Do not fall for that must replace shaft and not repair bunk.
That shaft can be repaired take it to a MACHINE SHIP not necessarily a "marine machine" shop what ever that may be.
I had the shafts on my boat, see the pic. , done 3 or 4 times over the 25 years that I had it and had them straightened several times.


I told many people over the years that if they purchased new shafts because the shop said so to please give the old ones to me! Do not leave with the shop as they will repair and resell.


I even had the shafts on my rudders done one time.

CCC

 

[DDW]

To close the story: I took the shaft to Olympic propeller, the knowledgable guy there (Ron) said "ah, I've seen a lot worse" and checked it for straightness - for free (well, I did have the prop trued there a few weeks ago). It was within 0.002. Put it back together with new cutlass bearings, spins freely now. Ran the engine on the hard, good flow of water observed from the shaft log. Put the boat in the water and motored to the slip.

Still don't know the cause of the problem originally. The tight (old) cutlass bearing is still tight - cannot be pushed onto the shaft with any normal force.

I am looking for a flow sensor to put in the water line that feeds the shaft log. Seems like you could get a stoppage (let's say a piece of zinc lodged in a fitting but then dropped away when you shut down). You'd never know. Engine cooling you have instrumentation to tell you.

 

[twistedtree]

Shaft alignment was originally suspected, but it was pretty much right on. The cutlass bearing has simply swollen up and gotten tight. When the transmission coupler was unbolted, there was no difference, still very hard to turn. With the shaft and cutlass removed, it will not slide onto the shaft easily and cannot be turned by hand. Cause unknown. The aft cutlass is also slightly tight, but can be turned. The new ones slide on with about 0.005 clearance, per spec. The old cutlass has no impression of the scoring, and is not worn more on one side than another.

The setup has a raw water supply piped from the engine raw water pump, through the transmission cooler. This is required for the Tides lip seal. Obviously this needs to be checked for flow. The silt or other deposits on the shaft indicate low or no flow. The boat has been operated on a fresh water lake for the last 9 years, not particularly shallow.

I had a cutlass bearing swell up and bind badly. It happens.


My concern would not be the scoring, but the pitting. When it's really bad, that can permeate the whole shaft and create swiss cheese. I'm not sure how to tell the extent, but it might be worth some research.

 

[FF]

"I'm not sure how to tell the extent, but it might be worth some research."

Pink, or Swiss cheese , the hassle is the prop falls off.

Usually on shifting into reverse.

 

[DDW]

The pitting that I saw was unlike any pitting I've seen. They were small crescent shaped dings, like you'd hit it not square with a very small hammer or perhaps it had been welded and not ground completely flush. Neither of these has happened. It remains a mystery. They were not deep.

 

[AKDoug]

Crevice corrosion?

 

[twistedtree]

Crevice corrosion?

Just erase the question mark. It's classic stainless crevice corrosion. Steve D'Antonio has one or more articles on the subject. Just check out his web site.

 

[AKDoug]

I was thinking the very tight cutlass bearing would contribute to a no oxygen condition and cause crevice corrosion. I have never seen it first hand before, but that made perfect sense to me...

 

[DDW]

Crevice corrosion is unlikely given that it's Aquamet 19 and in fresh water. Though possible I guess.