cutlass bearing

[Gerry]

I have just taken my Bowman 40 out to antifoul and a lot of boats in the yard are redoing their cutlass bearings. Does not seem to me that we have any play certainly under 2mm but concensus seems to be it shouild be replaced. I am not so sure.... As Bowman cannot give me any advice I wondered if any of you have knowlege. She is 1991 has a 1 and 1/4 inch shaft and we have had no vibration problems at all, do far! In the Canaries at the moment and if it does need replacing would rathjer wait until reaching the caribean in Jan. What do you think? I tend to belong to the , if it ain´t broke don´t fix it brigade but don´t want to be stupid. If it does need fixing what sort of bearing do you think it might need?
All opinions most welcome, many thanks

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[capsco]

With 2mm play it is indeed not broken, therefore you have answered your own question.

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[jerryat]

Hi Gerry,

2mm play seems a hell of a lot to me when you consider the thickness of the bearing material when new!! Westerly (and others) advised changing the bearing when play exceeded 25 thou/inch, so 2mm is obviously way beyond that. Whilst 25 thou may seem a bit low, I have just removed mine after 20 years service as part of a major refit with the play around 25-30 thou, and note that the new bearing is a snug, but not tight fit.
I'm surprised you don't hear the shaft rattling and in your place, about to shove off to the Caribbean, I'd definitely change it.

Be interesting to hear what others think.

Cheers, Jerry

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[robert_gainer]

If you can shake the shaft and feel it moving back and forth I think you should replace it. Just my thought on it.

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[boatmike]

Without being pedantic it's a cutless bearing (common mistake) The principle of a cutless bearing is in fact to create a hydraulic pressure between the shaft and the bearing. If this pressure is sufficient you need not worry at a little clearance. At 2mm I would say the bearing has certainly worn but probably still has a lot of life in it. If the shaft, prop, and coupling are reasonably in balance and you dont suffer vibration I would personally leave it and check next time to see if the wear has increased.

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[AndrewJ]

I don't know about the 2m clearance, but I learned recently that more wear comes in a vertical direction on the cutlass bearing. In other words if you move the shaft back and forth, it may have a little play, but if you lift the shaft and you have more play, than perhaps you need to replace the cutlass. (at least this is what the surveyor told me)

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[brianhumber]

You say under 2mm but 2mm on c30mm shaft is a 'rattling good fit' in bearing terms.
You may not be feeling vibration but you should note the rate of wear increases as the bearing clearance increases.
New Cutlass bearings are very inexpensive and with the proper tools and care in removing grub screws etc can be done quickly and easily.
Running with a sloppy bearing puts additional strain on the flexible coupling and shaft seal as well as wearing shaft in way of the bearing. It may not be 'broke' but you are accelerating hidden damage elsewhere on your transmision shafting.


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[Trevor_swfyc]

Hi Gerry,
Look at it this way do you only replace your anodes when all the zinc has gone, do you only change the oil when it no longer lubricates, do you replace valves only after the handle falls off, if the answer is no then the same should apply to your cutlass bearing.
The only way to inspect for wear is to remove the bearing and if you do that you might as well replace it. It will be worn to a degree and the extent will depend on many variables such as the amount of abrasive material held in suspension in the waters you operate in.
You are right to be concerned about fitting the right one, I took my shaft, old cutlass and cutlass holder to the Volvo agent. Getting the fit wrong would be worse than continuing to use the old one, no names but I have seen somebody force a cutlass onto a shaft with a hammer, when I questioned the wisdom of this he said it would wear in, Ho Hum. /forums/images/icons/frown.gif
All the best.
Trevor

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[AndrewB]

Interesting to read the different takes on this.

On my yacht, I know that 2mm play would be far, far too much, and would mean quite unacceptable viabration. I notice the vibration at about 1mm play and aim to change before this amount. (This measurement means the shaft can be moved sideways or up-and-down a total of 1mm, without compressing the nitrile). Normally I change the bearing about every 3 years, but if the engine has got out of alignment for any reason, the cutlass bearing wears quicker.

The bearing is an expendible component, intended for routine user replacement. When you've done it once, in future it shouldn't take you more than an hour with the boat out, and probably less.

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[boatmike]

Agreed, but the actual clearance in a cutless bearing should be a tight fit anyway. They are as I said before designed to run on hydraulic pressure NOT on the rubber and too close a fit will in fact promote rapid wear. The actual clearance tolerated will depend on the length of the shaft. the size of the prop, RPM and lots of things. It is a common misconception that there should be no play and the manufacturers are not going to discourage you from fitting new ones are they?
I agree that at about 1mm, especially if you have a relatively short shaft, it's getting time to replace if you are getting vibration. Yes of course engine alignment is critical too. This guy said he had less than 2 mm though and he is not suffering vibration at all. In that case I would personally not feel it essential to replace, but to check when he gets over the pond (which was his original question) My bet is that having worn to this degree the bearing will not wear rapidly from this point and will last quite a long time.....





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[Gerry]

Thank you all! Now in a state of confusion...... but I am a woman! In fact have gone back in the water, will change bearing next time we come out, hopefully in the caribean but keep a close eye on it in the meantime.

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