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Old 09-14-2018, 01:57 PM   #1
DDW
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Cutlass bearing scoring - how much is too much?

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?

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Old 09-14-2018, 02:07 PM   #2
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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.

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Old 09-14-2018, 02:16 PM   #3
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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.
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Old 09-14-2018, 09:23 PM   #4
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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.
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Old 09-14-2018, 10:57 PM   #5
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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.
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Old 09-15-2018, 12:02 AM   #6
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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.
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Old 09-15-2018, 12:10 AM   #7
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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.
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Old 09-15-2018, 08:04 AM   #8
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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, ...
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Old 09-15-2018, 08:37 AM   #9
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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.
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Old 09-15-2018, 09:34 AM   #10
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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.
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Old 09-15-2018, 09:49 AM   #11
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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.

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Old 09-15-2018, 12:44 PM   #12
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Quote:
Originally Posted by DDW View Post
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
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Old 09-15-2018, 01:12 PM   #13
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Quote:
Originally Posted by O C Diver View Post
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.
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Old 09-15-2018, 01:39 PM   #14
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"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.
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Old 09-15-2018, 03:56 PM   #15
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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.
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Old 09-15-2018, 11:05 PM   #16
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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.
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Old 09-15-2018, 11:18 PM   #17
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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.
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Old 09-16-2018, 05:45 AM   #18
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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.

Quote:
Originally Posted by DDW View Post
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.
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Old 09-16-2018, 09:27 AM   #19
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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.
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Old 09-16-2018, 10:58 AM   #20
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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
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