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Thread: Tolerance in cutlass bearing

  1. #1
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    Default Tolerance in cutlass bearing

    I just tried my new 25mm cutlass bearing on my shaft which is definitely 25mm and I gotta say the looseness of the bearing surprised me. I haven’t measured it but it’s very rattly,maybe a mm clearance in diameter.

    is that normal??

    Also I’m fitting this in a f’glass sterntube so I need two set screws to “locate” the bearing and I need two dimples for these to grip. Is there a guide as to how deep these need to be ? It’s one of those composite shells on the bearing not bronze. Looks about 1/8” thick wall . Would a 1/32” be enough?
    Last edited by Andrew Donald; 05-27-2020 at 06:01 AM.

  2. #2
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    Default Re: Tolerance in cutlass bearing

    Is the shaft itself maybe in those inch thingys ?

  3. #3
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    Default Re: Tolerance in cutlass bearing

    No def 25mm. Measured it in three places , brand new. ‘Sides that’d make it tighter. Dark and cold here now I’ll measure the bearing tomorrow
    Last edited by Andrew Donald; 05-27-2020 at 06:21 AM.

  4. #4
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    Default Re: Tolerance in cutlass bearing

    Is it an off-brand bearing?

  5. #5
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    Default Re: Tolerance in cutlass bearing

    A shaft should not have any noticeable play in a traditional cutlass bearing

  6. #6
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    Default Re: Tolerance in cutlass bearing

    Clearance tolerances here: http://www.pacificmarine.net/enginee...-clearance.htm

    Note* the interference fit will affect the clearance.

  7. #7
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    Default Re: Tolerance in cutlass bearing

    Measured internal of cutlass today and it’s 25.4mm

    Amazing how loose 0.44mm (~1/32” ish) feels but I’m happy now it’s only that much.
    Turn off the alarm!

  8. #8
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    Default Re: Tolerance in cutlass bearing

    25.4 That is exactly one inch!

  9. #9
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    Default Re: Tolerance in cutlass bearing

    Quote Originally Posted by Canoeyawl View Post
    25.4 That is exactly one inch!
    that it is and my shaft is 25mm so things look ok

  10. #10
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    Default Re: Tolerance in cutlass bearing

    1/2 mm is double the recommended maximum recommended clearance, or 4 times the minimum.
    (I think your original hunch was good and it is too loose, you may not have a "metric" bearing)

    https://www.duramaxmarine.com/pdf/Jo...essCatalog.pdf
    pp19
    7088399A-B002-40FF-9E97-86CA1573E904.jpg

  11. #11
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    Default Re: Tolerance in cutlass bearing

    If shaft is 25mm and bearing is 25.4 doesn't that mean the clearance is 0.2? Or is that not the correct way to look at it?

    Nevertheless, I'd be happier without any noticeable play. Is it possible to shim the bearing or the shaft, Andrew? I think I'd check with a marine engineering shop.
    Rick

    Lean and nosey like a ferret

  12. #12
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    Default Re: Tolerance in cutlass bearing

    I'll chime in here as I'm not sure the concerns about clearance have been clear:
    A new cutless should not have any appreciable play at all. After a couple years, sure, but not out of the box. Starting with a big clearance will allow the shaft to "orbit" withing the bearing, and the wear is in the gearbox output bearings/seals. The concern I see is confusion between a "25mm" shaft and an actual 24.5 bearing, it sounds like a mix of a metric size (25mm, which is really 25mm) and an imperial size (24.5mm, which is really 24.5mm). With your 25mm shaft, I think you need a 25mm bearing. Not trying to create undue anxiety, I well understand availability problems (living these 50 years smack in the middle of the North Pacific, its a constant problem) but in this case I really think patience to get a 25mm cutless will be rewarded with long service, and haste to make do will hurt in the longer run. Been following and enjoying the project Andrew, please carry on sharing and I hope I'm not raining unduly on your building parade!
    Brian

  13. #13
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    Default Re: Tolerance in cutlass bearing

    Brian , I’m assuming where you’ve written 24.5 you mean 25.4 (one inch)
    I hear where you’re coming from and come Monday I’m going to ring and check with supplier. Sealed Packet was marked 25mm.
    part of my reasoning to stick with the above mentioned clearance is that I have flexible engine mounts and solid coupling so a bit of play in cutlass May be required???
    I also have jumped the gun a bit And begun making my f’glass sterntube with said bearing in place, but hopefully the Vaseline I lubed outer of bearing with should enable me to remove it.

  14. #14
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    Default Re: Tolerance in cutlass bearing

    Ooops, yes, you understood what I meant rather than what I wrote...danged digits trading places when I'm not paying enough attention
    BQ

  15. #15
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    Default Re: Tolerance in cutlass bearing

    Quote Originally Posted by RFNK View Post
    If shaft is 25mm and bearing is 25.4 doesn't that mean the clearance is 0.2? Or is that not the correct way to look at it?

    Nevertheless, I'd be happier without any noticeable play. Is it possible to shim the bearing or the shaft, Andrew? I think I'd check with a marine engineering shop.
    Bearing clearance is the difference in diameter (id/od) not radius. Which on that shaft bearing combo should be between .003-.008 inches or .08-.2mm
    What I understand is, he now has .4mm or .016 (or double the max allowable clearance) This would read as "worn out", "must be replaced".
    Edit: .2 mm clearance on a 25mm rubber cutless bearing would be difficult to "feel" any play, but measurable with a dial indicator.
    Last edited by Canoeyawl; 05-30-2020 at 04:14 PM.

  16. #16
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    Default Re: Tolerance in cutlass bearing

    Just got a second bearing that was posted direct from importer - b%4#dy wrong too. Rang another company and they’ve got one of another brand that’s better by the sound of it. Get my money back from first mob and go elsewhere

    be wary when you buy a Vetus cutlass bearing

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