Does cutless bearing life vary depending on initial rubber thickness?

[jaffadog]

I am redoing my sterntube and shaft and juggling various size options. I am wondering whether the service life of the cutless bearing is at all related to how thick the rubber portion of the bearing is to begin with.

Compare these choices:

1. 1-1/2" ID sterntube; 1-1/4" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/8"; so maybe the rubber portion of that is 1/16"

-or-

2. 1-1/2" ID sterntube; 1" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/4"; so maybe the rubber portion of that is 1/8" or more

I'm wondering if option 1 will "wear out" more quickly than option 2. I'm inclined to think it would, because the channels for water to get into the bearing are so small, so water lubrication is less effective. And the rubber is so thin, that you don't have to lose much before you're through to brass.

Has anyone found this to be true? Or would the service lives of the bearings above be practically the same?

Thanks!
Jeremy

[David M]

Cutlass bearing life is more determined by the engine/transmission alignment to the shaft and how true (correctly pitched and balanced) the propeller is.

[delmarrey]

Originally Posted by jaffadog

I am redoing my sterntube and shaft and juggling various size options. I am wondering whether the service life of the cutless bearing is at all related to how thick the rubber portion of the bearing is to begin with.

Compare these choices:

1. 1-1/2" ID sterntube; 1-1/4" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/8"; so maybe the rubber portion of that is 1/16"

-or-

2. 1-1/2" ID sterntube; 1" shaft; effective wall thickness of the cutless bearing (brass and rubber) is 1/4"; so maybe the rubber portion of that is 1/8" or more

I'm wondering if option 1 will "wear out" more quickly than option 2. I'm inclined to think it would, because the channels for water to get into the bearing are so small, so water lubrication is less effective. And the rubber is so thin, that you don't have to lose much before you're through to brass.

Has anyone found this to be true? Or would the service lives of the bearings above be practically the same?

Thanks!
Jeremy

IMHO if the water is getting in there, all should be fine. If there were a thickness problem the manufacturers probably would not make them.
Wear is due to vibration and RPM. Being submerged in a forward/aft motion keeps them cool.

If it gets loose enough to hit brass, it should have been changed out long before. The bearing should be tight enough that it can't rattle.

Age is another factor. I had an old one once that the rubber started rolling up between the shaft and the rest of the rubber.

Never run one dry! When my boat's on the hard (90% of the time for now) I spray silicone in the bearing and cover it from the sun.

[Mark Zarley]

13 years and 37,000 nm cutlass bearing still tight. It is an alignment and balanced prop issue primarly and of a very minor secondary concern is the abrasives in the water you are running in. When doing an alignment it is more important to hold the shaft so it lines up with the cutlass bearing. The shaft log packing will run in and adjust to any small misalignment.

[colemj]

A cutlass bearing is considered worn when there is too much space between the rubber bearing surface and the shaft. This has nothing to do with how thick the original rubber bearing is.

Mark

[maxingout]

I have had Exit Only since 1993, and I sailed her around the world. We are a catamaran with two engines. I have only changed the cutlass bearings twice. Once in New Zealand, and once in Turkey. We have had good luck with our cutlass bearings.

[Rex Delay]

A major factor in the life of a cutlass bearing, along with alignment, is the water you are in. Here, if you keep it in the Fraser river with its massive silt load, they wear out fast. In clear water they can last a very long time.

[delmarrey]

Originally Posted by Rex Delay

A major factor in the life of a cutlass bearing, along with alignment, is the water you are in. Here, if you keep it in the Fraser river with its massive silt load, they wear out fast. In clear water they can last a very long time.

That's no joke! you can see the difference passing by.

.

[bobconnie]

You guy's got that right! the Fraser, Columbia, Klamath, running in there runoff is enought to wear out anyones cutlass bearings LOL found that out the hard way in the Columbia cruising from the mouth to Portland, 3 weeks on a new one, still on center to! worn out when we got back to Coos Bay. Bob and Connie course it was spring

[barnakiel]

Go for proper alignment first. Make sure the prop is well balanced. The thickness of the rubber will positively influence life only provided the two compared rubbers are of the same type, otherwise it is a wild guess as the finer rubber may be e.g. more resistant to wear (or not!).

b.

[colemj]

The thickness of the rubber has nothing to do with cutlass bearing life. Nothing at all. The cutlass bearing is bad when there is too much gap between the rubber bearing surface and the shaft. This has nothing at all to do with the initial thickness. Nothing at all. A 1/8" gap with the prop shaft is the same on a 1/4" bearing thickness as it is on 3" bearing thickness.

Mark

[jaffadog]

I agree with the notion that the bearing needs to be replaced when there is too much play - regardless of how much rubber is left. Nigel Calder suggests that anything more than minimal movement, defined as 1/16 per 1" of shaft diameter, warrants replacement of the bearing. Thing is, with option 1, there potentially is only 1/16 of rubber, after which I'd be getting metal on metal. Am I buying myself a headache if I go this route?

[delmarrey]

Originally Posted by jaffadog

I agree with the notion that the bearing needs to be replaced when there is too much play - regardless of how much rubber is left. Nigel Calder suggests that anything more than minimal movement, defined as 1/16 per 1" of shaft diameter, warrants replacement of the bearing. Thing is, with option 1, there potentially is only 1/16 of rubber, after which I'd be getting metal on metal. Am I buying myself a headache if I go this route?

I assume you mean 1/16 inch. That would be WAY too much for any recreational vessel.
.005" -.008" would be max for me. From the factory it's usually no more them .002", and sometimes with a little squeeze (zero tolerance) depends on the shaft tolerances. Once it starts spinning it's like a crankshaft bearing but lubed with water.

[4HMainer]

If your looking for longer service life then you may want to look alternatives to rubber as a bearing material, some composites have shown wear rates at around a third of that of rubber.
The clearances for when they need replacement are documented as are running clearances new as these are Lloyds approved for larger vessels.

Wear in a water lubricated bearing as others have said is mainly caused by alignment/vibration and also abrasive particles in the water. It is also effected by how often the shaft is run up or run down as most wear occurs at start up. Composites such as Maritex and Orkot have dry lubricants that prevent wear at these times.

The other major factor in warmer waters is marine growth on the shaft and on the bearing surface.

[Thumper74]

I bought the old Sabb 10hp gsp #970. A guy in Mississippi sold it to me. Can you reach out to me for questions and guidance ?? It’s going to be a direct replacement for another 10hp gsp although head is missing. So I am swapping motors. The boat is a 1975 albin25. Thanks

601-604-3462
Lkymnky77@gmail.com