mocruising
Well-Known Member
Does anyone know what is acceptible play in a water cooled/lubricated cutlass bearing measured in terms of mm.
Cutlass bearings.
- Thread starter mocruising
- Start date
Billjratt
Well-Known Member
Thought it was zero
Pye_End
Well-Known Member
Always a difficult one. Some say when you notice it getting worse!
TigaWave
Well-Known Member
Depends on what size of bearing we are talking about, ID and OD will effect the designed running clearance. As an example a 6" x 8" (IDxOD) has a running clearance of 0.6265mm.
I have heard people on small to medium leisure boats talk about 1.50mm as a rough guide as when to think about changing, but it often depends on if the wear accelerates or if you are doing a stern gear rebuild.
I have heard people on small to medium leisure boats talk about 1.50mm as a rough guide as when to think about changing, but it often depends on if the wear accelerates or if you are doing a stern gear rebuild.
CPD
Well-Known Member
What are the implications of excessive play ?
MoodySabre
Well-Known Member
This guy reckons 3/16ths of an inch
http://www.diybob.com/diyCutlessBearing.htm
http://www.diybob.com/diyCutlessBearing.htm
mocruising
Well-Known Member
4.7 mm seems a lot.
eyehavit
Well-Known Member
Consider changing the propeller shaft aft bearing when radial play approaches shaft diameter x 1.025 or as has been already said, if excessive vibration develops.
Excessive vibration places additional stress on gearboxes.
Excessive vibration places additional stress on gearboxes.
rex_seadog
Well-Known Member
If the cutless bearing is in a P bracket articles in PBOs 464 and 478 showed out to construct a puller to remove the bearing with the prop shaft left in situ. Send me a PM if you want more details. Also have a look at my posting 11/1/2006 and the many useful comments from other forumites.
Our Fulmar has now had 3 bearings in 3 seasons. Last year we moved the boat to the Dart and a local engineer changed the bearing between tides using a big hammer and a cut pipe to drift out the old bearing. I wasn't too happy with this and pushed hard against the P bracket with a big bolt of wood while he thumped. Luckily as the bearing had only been changed 12 months before it came out with very little effort. Even so we are now looking for a local (Brum) workshop who can knock up a suitable puller.
The boat is now out of the water and we didn't really experience any vibration at the end of this season. Maybe our new Dart mooring is kinder than than the Gosport one - we certainly didn't get any of the horrible grinding noises that we experienced in the first few seconds after putting the engine in gear that we used to experience following a few weeks without use on the Gosport mooring. However there definitely seems to be rather more vertical play than we would like. Perhaps we are just getting paranoid but we are considering changing it again anyway to ensure we don't have problems mid-season. Obviously we are anxious to diagnose the problem and will be looking at engine alignment and also for any calcified build-up on the prop shaft where it contacts the cutless bearing. Neither of these points were checked during the last twixt tide change.
Our Fulmar has now had 3 bearings in 3 seasons. Last year we moved the boat to the Dart and a local engineer changed the bearing between tides using a big hammer and a cut pipe to drift out the old bearing. I wasn't too happy with this and pushed hard against the P bracket with a big bolt of wood while he thumped. Luckily as the bearing had only been changed 12 months before it came out with very little effort. Even so we are now looking for a local (Brum) workshop who can knock up a suitable puller.
The boat is now out of the water and we didn't really experience any vibration at the end of this season. Maybe our new Dart mooring is kinder than than the Gosport one - we certainly didn't get any of the horrible grinding noises that we experienced in the first few seconds after putting the engine in gear that we used to experience following a few weeks without use on the Gosport mooring. However there definitely seems to be rather more vertical play than we would like. Perhaps we are just getting paranoid but we are considering changing it again anyway to ensure we don't have problems mid-season. Obviously we are anxious to diagnose the problem and will be looking at engine alignment and also for any calcified build-up on the prop shaft where it contacts the cutless bearing. Neither of these points were checked during the last twixt tide change.
Piers
Well-Known Member
On my Fleming, I began to notice that when in idle fwd gear, the shafts were 'singing'. When the boat was hauled out, there was maybe 1/16" play in both bearings (prop shaft is 2.25" diameter). I was advised there should be no play, otherwise the shaft is straining its engine coupling, quite apart from creating a more rapid wear of the bearing. Having changed them, no problems whatsoever. No-one was even able to tell me what had caused the wear in just 12 months of use....and now I've had 3 years use with no further 'singing'.
So, in answer to your qn, I can see no reason to have any play at all. Provided there is nothing to hinder the water flow through the bearing, they should last and last.
So, in answer to your qn, I can see no reason to have any play at all. Provided there is nothing to hinder the water flow through the bearing, they should last and last.
Tranona
Well-Known Member
Eating a cutlass a year suggests something seriously wrong. P brackets are good environment for the material as they get good flow of water. Have you checked your shaft size as some Westerlys had 25mm shafts and if you use a 1 inch bearing it is too big and will wear because the shaft is not supported.
TigaWave
Well-Known Member
As the gap between the shaft and the bearing increases it will allow shaft movement, shaft movement will mean the shaft will contact the bearing in places as it oscillates, this will cause localised wear ending up with a larger gap and greater forces, wear will accelerate as the gap increases.
Tolerances have to be closely controlled as too little clearance will mean the bearing can run tight as it warms up, or if run in warmer water.
Just the right clearance allows for a uniform film of water which supports the shaft centrally, so that the shaft only contacts the bearing at rest, some bearings have non leaching lubricants for this start up phase when effectively the bearing is dry and most wear happens.
With regard to fitting, it is possible to have some bearings made as a clearance fit, which can then be slid into place. If the bearing can rotate freely in the bearing carrier with the shaft supported it guarantees shaft bearing alignment, bedded on epoxy they can also be easily removed without the need for excessive force.
I hope this helps.
Tolerances have to be closely controlled as too little clearance will mean the bearing can run tight as it warms up, or if run in warmer water.
Just the right clearance allows for a uniform film of water which supports the shaft centrally, so that the shaft only contacts the bearing at rest, some bearings have non leaching lubricants for this start up phase when effectively the bearing is dry and most wear happens.
With regard to fitting, it is possible to have some bearings made as a clearance fit, which can then be slid into place. If the bearing can rotate freely in the bearing carrier with the shaft supported it guarantees shaft bearing alignment, bedded on epoxy they can also be easily removed without the need for excessive force.
I hope this helps.
nedmin
Well-Known Member
One of the best ways of telling if it wants changing is to lift the prop. shaft up and down quickly, if it makes a thumping noise when you do this it probably wants changing.Dont forget that when most cutless bearings dry out they shrink thus exaggerating the play.
charles_reed
Well-Known Member
Re: Cutless bearings.
Varies depending on bearing backing and shaft diameter, but for a brass-backed cutless on a 30mm shaft 4-5mm.
Varies depending on bearing backing and shaft diameter, but for a brass-backed cutless on a 30mm shaft 4-5mm.
charles_reed
Well-Known Member
It just goes to show
you shouldn't believe all you're told.
There is no such thing as a bearing without some clearance.
When in the water most cutlesses swell and the additional layer of water takes up some of the space.
you shouldn't believe all you're told.
There is no such thing as a bearing without some clearance.
When in the water most cutlesses swell and the additional layer of water takes up some of the space.
vyv_cox
Well-Known Member
Over the past few years we have experienced an increasing range of revs in which there has been considerable vibration. Having changed everything else, we now conclude that the problem is wear of the shaft. Swimming beneath the boat there is an audible bump and evident slack if the shaft is lifted or shaken side to side. The cutless bearing is almost new and initially appeared to be a good fit, although I suspect that this was only over a very short length of the worn journal. I am about to fit a new shaft and estimate the wear of the shaft to be about 0.5 -1.0 mm, so a diametrical clearance of 1 - 2 mm or a little more.
TheBoatman
Well-Known Member
Re: Cutless bearings.
Charles
Sorry but there is no way that 4-5mm of clearance on any bearing could be considered as being acceptable.
When the boat is lifted from the water you should carryout a couple of quick checks.
1. Turn the prop and it should "squeak" in the bearing.
2. Grab the prop and try and move it up & down & side to side.
If you have no squeak and it moves in either direction ~ change the bearing!
Peter.
Charles
Sorry but there is no way that 4-5mm of clearance on any bearing could be considered as being acceptable.
When the boat is lifted from the water you should carryout a couple of quick checks.
1. Turn the prop and it should "squeak" in the bearing.
2. Grab the prop and try and move it up & down & side to side.
If you have no squeak and it moves in either direction ~ change the bearing!
Peter.
longjohnsilver
Well-Known Member
That's interesting Piers cos I've just had my cutlass bearings changed and when we launched 2 days ago there was a distinct singing from the shafts/props at lower revs. But it can't be wear on the bearings!!
Piers
Well-Known Member
Interesting indeed.
Well, it certainly cured it for me. Put it this way. The shafts started singing (whilst going up the Seine - sounded great in the locks!), the boat was hauled some 100 hours later, there was play in the bearings (1/16", maybe slightly more), they were changed, since when no problems at all.
I'd love to know what you find. Meanwhile, I'll ask the engineer and see if he's heard of other causes of 'singing'. Did it literally only occur after the new bearing were fitted on your new boat?
Well, it certainly cured it for me. Put it this way. The shafts started singing (whilst going up the Seine - sounded great in the locks!), the boat was hauled some 100 hours later, there was play in the bearings (1/16", maybe slightly more), they were changed, since when no problems at all.
I'd love to know what you find. Meanwhile, I'll ask the engineer and see if he's heard of other causes of 'singing'. Did it literally only occur after the new bearing were fitted on your new boat?