cutless bearing movement

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saltyrob

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Hi folks,

At the end of last season I noticed that there was movement between between the cutless bearing and shaft. The shaft is one inch diameter and only three seasons old. I have purchased a new bearing and prior to fitting have tried it on the shaft .There still seems to be movement between the shaft and new bearing at the p bracket and other locations on the shaft where it would not be subject to wear.Have checked the shaft and confirmed that it is one inch in diameter.Other boats in the yard appear to have no movement between their shafts and bearings. Am I worrying to much and is a little movement ok.

Many thanks


Robert
 
A little movement is OK, I'd say a mill or less is OK, maybe up to 2mm. There is alway a small amount of play.
 
That is what I found last year as well. The play on the original shaft/bearing combo was about 1.5mm and there was a rumble when driving. The new bearing also had perceptible play. I had checked the shaft, both with a digital caliper and an old screw micrometer and the wear was only 16 thou, which made the shaft exactly 25 mm at the contact region!

The local engineers looked at the shaft and agreed hat the wear was slight, but detected that there was also slight pitting, albeit outside the contact zone. The shaft was also renewed and the new combo showed no play whatever intitially and there is still none after one season of use.
 
Salty,
If you have a 1" diameter shaft and the play, specifically the radial displacement, measures more than 20 mil, 0.020", 20 thou, or expressed in mm, 0.51mm, that it is time to replace the bearing/check shaft for wear.
With modern hydrodynamic bearing materials, if the radial displacement between a 25.4mm shaft and bearing, when newly installed, measured anywhere near 0.5mm, it should be rejected.
 
Is the bush material resin or bronze? The resin ones are intended to be a little sloppy when fitted because the bush will swell a little when immersed in water. Mine was a little loose when new but no movement after a day or so after launch.
 
Are you fitting it with a clearance fit in the P bracket or an interference fit? With an interference fit you will get some bore closure. But best way to fit is clearance and bed on epoxy, that way you can ensure the bearing and shaft are aligned in the P bracket.
 
In normal use, seawater acts as lubricant between the cutless bearing and the shaft. The downside of too much movement between the two is, in the short term, that the stern gear will rumble as the shaft rotates in its bearing - not in itself life threatening. But wear will occur on the shaft - easy to see when the shaft is slid forward for inspection. Again nothing is going to happen immediately as a result of this. If you are operating in sandy water, particles will more easily ingress and accelerate wear on both bearing and shaft.

In my view there are other things on a boat more worthy of the marginal dollar than ensuring there is no slack, ever, on the cutless bearing.

PWG
 
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