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  1. #1
    Join Date
    Jan 2009
    Posts
    96

    Default Play in new Cutlass

    Hi all,

    Just installed a new cutlass bearing in P bracket that takes a 25mm shaft. I was expecting the shaft to be a tight fit in the new bearing so put plenty of soap on the rubber flutes, I was very surprised to find that the shaft nearly fell out the other side when I pushed it into the bearing. With the shaft positioned correctly I could detect a small amount of play between the shaft and bearing and I could turn the shaft without any resistance.

    I was expecting a brand new bearing to be a tight fit, to give some resistance to turning by hand and I wasn't expecting any play initially until after a couple of hours use when things were bedded in. Is this correct?

  2. #2
    Join Date
    Jun 2010
    Posts
    699

    Default

    You may have fitted a 1-inch cutless bearing - that equates to 25.4mm and would account for the play.

  3. #3
    Join Date
    Jan 2009
    Posts
    96

    Default Wrong bearing

    That was my intial thought so I re measured the shaft at various places including the bearing surface which came in at 24.95mm, I then checked the bearing and gently measured the ID between flutes, this was approx 25.3 following which I concluded I'd been given a 1" bearing by mistake.

    I have just ordered another two bearings specified as 1.5" OD (38.1mm) and 25mm ID from two different suppliers, I've checked the ID in the same way and they both measure approx 25.3 so now I'm not so sure that the original one is incorrect, it maybe that when measuring across the rubber I'm digging into the surface afraction and over reading.

    If the bearing is the right size for the shaft I wouldn't now where to turn next other than to question my expectation of a snug fit.

  4. #4
    Chaktoura is online now Registered User
    Location : Southampton / Chichester
    Join Date
    Feb 2007
    Posts
    284

    Default

    I have just gone through exactly the same thing. When I asked the chap who fitted it he said that the bearings expand slightly when immersed.

  5. #5
    vyv_cox's Avatar
    vyv_cox is offline Registered User
    Location : North Wales, sailing Aegean Sea or Menai Strait
    Join Date
    May 2001
    Posts
    15,158

    Default

    Is it brass or phenolic backed? The phenolic ones do swell in water but the amount does not seem closely controlled. After a week or two in water mine was very tight, so I only fit brass ones now.
    Answers to some technical queries at http://coxengineering.sharepoint.com

  6. #6
    Join Date
    Jan 2009
    Posts
    96

    Default Brass or Phenolic

    Its your common brass shelled nitrile rubber inner bearing. Is Nitrile rubber hydroscopic?

  7. #7
    vyv_cox's Avatar
    vyv_cox is offline Registered User
    Location : North Wales, sailing Aegean Sea or Menai Strait
    Join Date
    May 2001
    Posts
    15,158

    Default

    Quote Originally Posted by Amp1ng View Post
    Its your common brass shelled nitrile rubber inner bearing. Is Nitrile rubber hydroscopic?
    Not to an appreciable extent. Many elastomers swell one or two percent in water but probably not enough to take up bearing clearance.
    Answers to some technical queries at http://coxengineering.sharepoint.com

  8. #8
    ithet is offline Registered User
    Location : UK, Hamble
    Join Date
    Mar 2009
    Posts
    269

    Default

    I have a similar problem with 1inch bearing, very loose then wears out quickly. Have been using Vetus brass shell. Will try different type this year (open to suggestions).

  9. #9
    Join Date
    Oct 2004
    Posts
    1,603

    Default

    No bearing should ever be a tight fit and bed in. Simply because it will be running dry if there is not enough room for a water film do develop. In rubber this will mean rapid wear and not necessarily even wear as the shaft will flex and run around.

    Bearings should come with a known clearance.

    Our shaft bearings for 25.00mm shaft 1.5" carrier have an ID 25.12-25.22
    1" 25.40 shaft is ID 25.52 - 25.62

    This clearance allows for moisture 0.0375mm and thermal 0.06mm expansion.

    Change when clearance gets to or approaches 0.6mm
    quicKutter rope cutter, shaft and rudder bearings
    www.h4marine.com

  10. #10
    Join Date
    Jan 2009
    Posts
    96

    Default

    Thanks for the responses everyone.

    I'll go back down and re assess the play that i thought i could detect. Maybe because I was expecting a tight bearing to shaft fit I have incorrectly assumed there is a problem with the new installation.

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