Cutlass Bearing play

[LadyInBed]

Having just replaced mine, the bearing had worn from 20 to 22 mm diameter.
Had I left it in too long, could it have been left in longer or was a 10% play about the right point for replacement?

 

[dombuckley]

I think you timed it about right. Areas of fairly shallow water with strong tides (such as the Severn and Thames Estuaries) give rise to a lot of silty water, so you will find a relatively high rate of wear due to suspended particles in the water. You would not have wanted to wait another year.

 

[Neil_Y]

For a 20.00mm shaft we would suggest changing the bearing when radial displacement approached 0.50mm
New the bearing would have 0.12 min radial displacement (or bearing ID 20.12 min)

 

[LadyInBed]

For a 20.00mm shaft we would suggest changing the bearing when radial displacement approached 0.50mm
New the bearing would have 0.12 min radial displacement (or bearing ID 20.12 min)

Are you saying - Replace when 5% play?

 

[Neil_Y]

No, 2.5% of shaft diameter is considered by Maritex bearings as a good time to replace. In trials it takes them three times as long as other bearings to get to this level of wear though so it doesn't mean they are replaced any more frequently.

As the gap increases and the water film increases it can support less pressure and hence will allow the shaft to bend and move from side to side (rather than restricting it) Normally we expect to see an increase in vibration/noise by this time, but often on smaller boats with less hp it is less noticeable, and owners change when things are getting pretty sloppy.

 

[chrishelen]

No, 2.5% of shaft diameter is considered by Maritex bearings as a good time to replace. In trials it takes them three times as long as other bearings to get to this level of wear though so it doesn't mean they are replaced any more frequently.

As the gap increases and the water film increases it can support less pressure and hence will allow the shaft to bend and move from side to side (rather than restricting it) Normally we expect to see an increase in vibration/noise by this time, but often on smaller boats with less hp it is less noticeable, and owners change when things are getting pretty sloppy.

How much 'play' should there be in a new cuttlas bearing?

 

[NickRobinson]

" but often on smaller boats with less hp it is less noticeable, and owners change when things are getting pretty sloppy.
"
So true. In my ignorance I used my first inboard engine boat with nearly 3/16" play on a 3/4" shaft for hundreds of miles. (8hp Yanmar- so much noise and vibration from that I would not have noticed if the prop dropped off!)

 

[chrishelen]

" but often on smaller boats with less hp it is less noticeable, and owners change when things are getting pretty sloppy.
"
So true. In my ignorance I used my first inboard engine boat with nearly 3/16" play on a 3/4" shaft for hundreds of miles. (8hp Yanmar- so much noise and vibration from that I would not have noticed if the prop dropped off!)

The boat yard fitted a new 25mm shaft and bearing today, I can move the shaft around by about 0.5 mm, the fitter says its OK, well he would, wouldn't he?

 

[LadyInBed]

Replaced Apr 13 - I had better check it next time I dry out

 

[NickRobinson]

The boat yard fitted a new 25mm shaft and bearing today, I can move the shaft around by about 0.5 mm, the fitter says its OK, well he would, wouldn't he?

My shaft required welding and turning as it had a very visible neck. Fortunately done FOC. Even after renewing it had a bit of slap. Before it was c. 5mm!

 

[chrishelen]

My shaft required welding and turning as it had a very visible neck. Fortunately done FOC. Even after renewing it had a bit of slap. Before it was c. 5mm!

Thanks, gave my surveyor a ring to get his opinion, he was happy with it, but I still think it was a bit sloppy, perhaps a metric bearing on a imperial shaft. I need to see the paper work.

 

[vyv_cox]

The boat yard fitted a new 25mm shaft and bearing today, I can move the shaft around by about 0.5 mm, the fitter says its OK, well he would, wouldn't he?

Is it a brass or plastic housing? Plastic ones are made with excessive clearance to allow for swelling when it is immersed. I found this a bit hit-or-miss and the bearing became very tight. I changed it out for a brass one after one season.

 

[chrishelen]

Is it a brass or plastic housing? Plastic ones are made with excessive clearance to allow for swelling when it is immersed. I found this a bit hit-or-miss and the bearing became very tight. I changed it out for a brass one after one season.

Its a plastic one, the engineer said it might swell up after a while.

 

[macd]

How much 'play' should there be in a new cuttlas bearing?

Answered by Neil_Y in post #3.

 

[chrishelen]

Is it a brass or plastic housing? Plastic ones are made with excessive clearance to allow for swelling when it is immersed. I found this a bit hit-or-miss and the bearing became very tight. I changed it out for a brass one after one season.

Lots of vibration coming from somewhere on the boat today that wasn't there before they ' fixed,' it...why can't you get a good job done first time these days it seems?

 

[Heckler]

The boat yard fitted a new 25mm shaft and bearing today, I can move the shaft around by about 0.5 mm, the fitter says its OK, well he would, wouldn't he?

Both my Benes, 351 and 381, had/have half to one mill play even when the bearings are new. No, the shaft isnt worn.