Play in new Cutlass

[Amp1ng]

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?

 

[greenalien]

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

 

[Amp1ng]

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.

 

[Ammonite]

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.

 

[vyv_cox]

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.

 

[Amp1ng]

Brass or Phenolic

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

 

[vyv_cox]

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.

 

[ithet]

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).

 

[Neil_Y]

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

 

[Amp1ng]

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.