Norman_E
Well-Known Member
Just how much play is acceptable before the bearing needs replacement?
Cutlass bearing
- Thread starter Norman_E
- Start date
Krusty
Well-Known Member
5 per cent of diameter, (1.5mm for a 30mm shaft) judging by what my surveyor has just passed as 'satisfactory condition',
Hope that helps, until someone with more authority on the subject comes along.
Hope that helps, until someone with more authority on the subject comes along.
Norman_E
Well-Known Member
In that case mine is just about OK, but I will take another look at it when I go to Turkey this month.
plankton
Member
Hi mine had about a mm movement up and down the surveyor figured it okay for another season but as i was embarking on a longish voyage the yard advised i get it done and they found it had already worn/damaged the shaft itself so all had to be replaced .. i have no real idea on this just this one experience but guess if its caught in time it might save a shaft replacement?..maybe better not to wait if you can wiggle it..but then maybe its always best to replace the shaft at the same time anyway? so you might as well get some mileage ! be interested to know a more qualified opinion..sorry if this is absolutely no help
Topcat47
Well-Known Member
Any discernable play in the cutless bearing is bad news. If you're ashore, and you must be to check it out, then replacing it is cheaper than putting the boat back in the water and having it removed later to do the job.
4% (1mm on a 25 mm shaft) may be OK short term but wear will increase exponentially and at this level, you can expect some addititional wear on the shaft seal.
I'd replace it!
4% (1mm on a 25 mm shaft) may be OK short term but wear will increase exponentially and at this level, you can expect some addititional wear on the shaft seal.
I'd replace it!
Norman_E
Well-Known Member
My boat is in Turkey, and I am thinking of changing the bearing, but cannot remember the shaft diameter, which I need to make up a tool to force the old bearing out anf push the new one in. Does anyone know the diameter of the shaft on a Jeanneau 45.2?
eyehavit
Well-Known Member
[ QUOTE ]
5 per cent of diameter, (1.5mm for a 30mm shaft) judging by what my surveyor has just passed as 'satisfactory condition',
[/ QUOTE ]
So pro-rata, on a 100mm dia. shaft, 5mm of displacement between shaft and bearing is "satisfactory". I would strongly argue that the bearing is well and truly due for replacement.
My rule of thumb for deciding when it is necessary to replace a propeller shaft bearing is when displacement approaches/reaches 2.5% of the shaft diameter. Using the same rationale, for a 30mm shaft the critical displacement is 0.75mm.
5 per cent of diameter, (1.5mm for a 30mm shaft) judging by what my surveyor has just passed as 'satisfactory condition',
[/ QUOTE ]
So pro-rata, on a 100mm dia. shaft, 5mm of displacement between shaft and bearing is "satisfactory". I would strongly argue that the bearing is well and truly due for replacement.
My rule of thumb for deciding when it is necessary to replace a propeller shaft bearing is when displacement approaches/reaches 2.5% of the shaft diameter. Using the same rationale, for a 30mm shaft the critical displacement is 0.75mm.
fastjedi
Well-Known Member
This isn't quite as straight forward as you might imagine. I decided to change mine last winter with about 1mm to 1.5mm of play ... and the new one ...... exactly the same.
Aaaahhh, It's the propshaft I here you say? No, it's a relatively new low hours boat.
Aaaahhh, It's the propshaft I here you say? No, it's a relatively new low hours boat.
eyehavit
Well-Known Member
It sounds more like a metric shaft/imperial bearing stuff up. Definetly a mis-match, but of course I am assuming the shaft is less than 150mm.
Krusty
Well-Known Member
Interesting series of posts following on my 5 per cent guess!
For general information: I last replaced the Cutless when installing a new Beta/Isuzu engine early 1989. That engine was replaced by a much better one (Beta/Kubota) together with a new, longer, shaft in 2003. At that time the play in the Cutless was less than 1mm, after 15 seasons hard use. Some of the wear was in the old shaft, so I chose not to replace the bearing. The play around the new shaft was well under 1mm.
Since then the engine has been used far more than previously, and the wear play is about 1.5 mm. I have taken note that wear is very likely accelerating, and plan to draw the shaft for examination next winter. Can't complain at a 20-year bearing life!
I don't know whether that is a long life, but if it is, I would list the reasons as:
1. P-bracket mounting gives the best water flow for lubrication,
2. Sailing mostly offshore, and in almost silt-free waters,
3. Care over alignment, and use of a tolerant flexible-coupling (Vetus Bullflex).
All constructive comments appreciated.
For general information: I last replaced the Cutless when installing a new Beta/Isuzu engine early 1989. That engine was replaced by a much better one (Beta/Kubota) together with a new, longer, shaft in 2003. At that time the play in the Cutless was less than 1mm, after 15 seasons hard use. Some of the wear was in the old shaft, so I chose not to replace the bearing. The play around the new shaft was well under 1mm.
Since then the engine has been used far more than previously, and the wear play is about 1.5 mm. I have taken note that wear is very likely accelerating, and plan to draw the shaft for examination next winter. Can't complain at a 20-year bearing life!
I don't know whether that is a long life, but if it is, I would list the reasons as:
1. P-bracket mounting gives the best water flow for lubrication,
2. Sailing mostly offshore, and in almost silt-free waters,
3. Care over alignment, and use of a tolerant flexible-coupling (Vetus Bullflex).
All constructive comments appreciated.
eyehavit
Well-Known Member
20 years is at the high end of bearing life expectancy.
As to whether or not 'P' 'V' or 'Y' brackets provide the best water flow for lubrication is debatable. However, it is true that to operate at maximum efficiency, hydrodynamic sleeve bearings require rapid establishment of a continuous film of lubricant, and for water lubricated bearings there must be sufficient water lubrication available to maintain a fluid film. When a vessel is underway, bracket bearings are automatically exposed to copius quantities of relatively cool pressurised lubricating water.
Whereas on one hand, surplus lubrication does not increase life expectancy, on the other hand, lack of lubrication does contribute to decreased bearing life. For hydrodynamic lubricated bearings, the thickness of lubricating film can contribute to bearing life. Factors affecting film thickness can be the viscosity of the lubricating medium, in this case water. Factors affecting viscosity can be temperature. Bracket mounted bearings receive the coolest water that is generally available for lubrication. It is not well known but cold lubricants, in this case water, have higher viscosity than warm lubricants (water), so all other things remaining equal, a lubricating fluid film seperating a shaft from a bearing will support more dynamic load if the lubricant is colder rather than warmer.
There are mechanical factors that contribute to bearing life and to list some of them:
Shaft length between bearings, (contributes to whip/whirling)
Shaft straightness, (contributes to whip/whirling)
Alignment of the drive train, (excessive pressure on one side of a bearing)
Propeller match and balance, (contributes to whip/whirling)
All of the above cause shaft and bearing to make dynamic contact to a greater or lesser degree.
Depending on severity, bearing wear may range from neglible/mild/'normal'/rather more than 'normal'/rapid/catastophic
Exposure to abrasive particles contributes to wear.
Possible casuses can be:
Sand/silt from manouvering in shallow water.
Sand/silt from crossing sand bars
Calcium carbonate grinding between shaft and bearing caused by sea growth permitted by infrequent turning of the shaft.
Generally, the larger the abrasive particle, the more rapid the wear.
In your case, Piota, other than changing to a longer shaft, you appear to have avoided most of the contibuting factors.
As to whether or not 'P' 'V' or 'Y' brackets provide the best water flow for lubrication is debatable. However, it is true that to operate at maximum efficiency, hydrodynamic sleeve bearings require rapid establishment of a continuous film of lubricant, and for water lubricated bearings there must be sufficient water lubrication available to maintain a fluid film. When a vessel is underway, bracket bearings are automatically exposed to copius quantities of relatively cool pressurised lubricating water.
Whereas on one hand, surplus lubrication does not increase life expectancy, on the other hand, lack of lubrication does contribute to decreased bearing life. For hydrodynamic lubricated bearings, the thickness of lubricating film can contribute to bearing life. Factors affecting film thickness can be the viscosity of the lubricating medium, in this case water. Factors affecting viscosity can be temperature. Bracket mounted bearings receive the coolest water that is generally available for lubrication. It is not well known but cold lubricants, in this case water, have higher viscosity than warm lubricants (water), so all other things remaining equal, a lubricating fluid film seperating a shaft from a bearing will support more dynamic load if the lubricant is colder rather than warmer.
There are mechanical factors that contribute to bearing life and to list some of them:
Shaft length between bearings, (contributes to whip/whirling)
Shaft straightness, (contributes to whip/whirling)
Alignment of the drive train, (excessive pressure on one side of a bearing)
Propeller match and balance, (contributes to whip/whirling)
All of the above cause shaft and bearing to make dynamic contact to a greater or lesser degree.
Depending on severity, bearing wear may range from neglible/mild/'normal'/rather more than 'normal'/rapid/catastophic
Exposure to abrasive particles contributes to wear.
Possible casuses can be:
Sand/silt from manouvering in shallow water.
Sand/silt from crossing sand bars
Calcium carbonate grinding between shaft and bearing caused by sea growth permitted by infrequent turning of the shaft.
Generally, the larger the abrasive particle, the more rapid the wear.
In your case, Piota, other than changing to a longer shaft, you appear to have avoided most of the contibuting factors.
Ruffles
Well-Known Member
[ QUOTE ]
Calcium carbonate grinding between shaft and bearing caused by sea growth permitted by infrequent turning of the shaft.
[/ QUOTE ]
That's what does for most privately owned boats IMO. And the imbalance caused by a fouled prop. I've changed mine this year. It was only 4 years old. The shaft under the bearing was white with scale.
Calcium carbonate grinding between shaft and bearing caused by sea growth permitted by infrequent turning of the shaft.
[/ QUOTE ]
That's what does for most privately owned boats IMO. And the imbalance caused by a fouled prop. I've changed mine this year. It was only 4 years old. The shaft under the bearing was white with scale.
vyv_cox
Well-Known Member
<<<<<... and the new one ...... exactly the same>>>>>>
Is it a plastic or bronze bush? The plastic ones are intended to be sloppy when first fitted, they swell after a day or so in the water. Mine was the same when I fitted it some years ago but ever since it has been tight except after a winter ashore.
Is it a plastic or bronze bush? The plastic ones are intended to be sloppy when first fitted, they swell after a day or so in the water. Mine was the same when I fitted it some years ago but ever since it has been tight except after a winter ashore.
vyv_cox
Well-Known Member
<<<<There are mechanical factors that contribute to bearing life and to list some of them:
Shaft length between bearings, (contributes to whip/whirling)
Shaft straightness, (contributes to whip/whirling)
Alignment of the drive train, (excessive pressure on one side of a bearing)
Propeller match and balance, (contributes to whip/whirling)
All of the above cause shaft and bearing to make dynamic contact to a greater or lesser degree. >>>
Some confusion in this statement.
Whirl occurs in plain bearings, i.e ones that are fully circular in the bore. Dividing the bearing up into segments, as in a tilting pad bearing, for which read a cutless bearing, prevents the necessary circulation of the lubricant in the nip and therefore overcomes whirl.
Whip is a phenomenon that occasionally occurs in machines subject to whirl, when the whirl frequency coincides with and becomes locked into a system’s natural frequency. It typically occurs at high revs, e.g 10,000 rpm. This is extremely unlikely in a propeller shaft.
The shaft length can have an effect, if the running speed coincides with the natural frequency of the shaft, in which case resonance can occur, leading to high displacement and bearing loads. Placing the shaft anode in the centre of the between-bearings length will exacerbate this condition. Shaft out-of-straightness and prop unbalance simply produce high lateral force, causing imbalance and higher bearing loads.
Shaft length between bearings, (contributes to whip/whirling)
Shaft straightness, (contributes to whip/whirling)
Alignment of the drive train, (excessive pressure on one side of a bearing)
Propeller match and balance, (contributes to whip/whirling)
All of the above cause shaft and bearing to make dynamic contact to a greater or lesser degree. >>>
Some confusion in this statement.
Whirl occurs in plain bearings, i.e ones that are fully circular in the bore. Dividing the bearing up into segments, as in a tilting pad bearing, for which read a cutless bearing, prevents the necessary circulation of the lubricant in the nip and therefore overcomes whirl.
Whip is a phenomenon that occasionally occurs in machines subject to whirl, when the whirl frequency coincides with and becomes locked into a system’s natural frequency. It typically occurs at high revs, e.g 10,000 rpm. This is extremely unlikely in a propeller shaft.
The shaft length can have an effect, if the running speed coincides with the natural frequency of the shaft, in which case resonance can occur, leading to high displacement and bearing loads. Placing the shaft anode in the centre of the between-bearings length will exacerbate this condition. Shaft out-of-straightness and prop unbalance simply produce high lateral force, causing imbalance and higher bearing loads.
eyehavit
Well-Known Member
[ QUOTE ]
Some confusion in this statement.
Whirl occurs in plain bearings, i.e ones that are fully circular in the bore. Dividing the bearing up into segments, as in a tilting pad bearing, for which read a cutless bearing, prevents the necessary circulation of the lubricant in the nip and therefore overcomes whirl.
[/ QUOTE ]
Dividing a plain bearing with segments, read lubricating grooves, enables fresh lubricant to be dragged by the rotating shaft to form a pressure wedge of lubricant between shaft and bearing. The effect of such a wedge is to provide lift, and when conditions are optimum, to lift a shaft clear of the bearing. The only circumstance that I am aware of when whirling does not occur, to a greater or lesser degree, is when displacement between shaft and bearing is exactly negated by the thickness of the lubricant.
Some confusion in this statement.
Whirl occurs in plain bearings, i.e ones that are fully circular in the bore. Dividing the bearing up into segments, as in a tilting pad bearing, for which read a cutless bearing, prevents the necessary circulation of the lubricant in the nip and therefore overcomes whirl.
[/ QUOTE ]
Dividing a plain bearing with segments, read lubricating grooves, enables fresh lubricant to be dragged by the rotating shaft to form a pressure wedge of lubricant between shaft and bearing. The effect of such a wedge is to provide lift, and when conditions are optimum, to lift a shaft clear of the bearing. The only circumstance that I am aware of when whirling does not occur, to a greater or lesser degree, is when displacement between shaft and bearing is exactly negated by the thickness of the lubricant.