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Thread: Refitting prop

  1. #1
    Join Date
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    Default Refitting prop

    Should be a simple one...refitting a bronze prop onto a stainless tapered shaft. Just clean the mating surfaces of each, or grease them? Just trying to avoid the shenanigans experienced recently of blowtorches, breaker bars, and prop pullers flying across the yard at Mach 3!

    Thanks!
    Sabre 27 134/49er GBR340/Foiling Moth GBR3116/Flying Fifteen K797/Fireball GBR14110

  2. #2
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    Never never use grease.....

    Lap taper in with fine valve grinding paste without key fitted, wipe off and clean up with brake cleaner. Check key is nice and snug in keyway. When refitting prop make 100% sure it is on the taper not riding on the key.

    Good time of the year to fit a prop, one left baking in the sun before fitting, now that makes removal a real challenge!

  3. #3
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    Quote Originally Posted by Latestarter1 View Post
    Never never use grease.....
    Why do you say that please?
    KiwiProp specifically recommend greasing the shaft, but that's for a stainless steel (316) hub and I guess you're talking bronze?
    Does it make a difference?

  4. #4
    Ruffles's Avatar
    Ruffles is offline Registered User
    Location : Boat: Portsmouth, Us: Stewkley
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    The first time I put a prop on a tapered shaft I greased it first. I noticed that I could easily tighten the nut beyond its original position. Fortunately I stopped at that point and took advice!

  5. #5
    TNT's Avatar
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    Default tapered prop

    The taper is not just there to centralise, it also locks the prop so most of the force/torque is not on the key but taken up by the fiction of the two tapers locking together, if you grease it you remove the friction and as already stated the next time you come to remove it, it will be a pig to get off.
    both surfaces clean and any dings removed, grinding paste is good (as already mentioned) just make sure both surfaces are clean otherwise any small particles will dig into both surfaces.
    "Engineers do it with feeler gauges"

  6. #6
    vyv_cox's Avatar
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    Remember when tightening the nut that it is a taper fit, not a conventional square one. The torque applied to the nut is effectively magnified by the ratio of the taper. The reason so many props are difficult to remove is that the nut was tightened using the torque appropriate to the thread size in conventional configuration. Tighten the nut with a short tommy bar or spanner and don't lean too heavily on it.
    Answers to some technical queries at http://coxengineering.sharepoint.com

  7. #7
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    Many thanks all. Vyv, as I do have a torque wrench, could you give me an idea of a suitable torque? Shaft is 1", and the nut is about 30mm across the flats.
    Sabre 27 134/49er GBR340/Foiling Moth GBR3116/Flying Fifteen K797/Fireball GBR14110

  8. #8
    vyv_cox's Avatar
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    I'm really struggling to find a torque figure. Advice for most tapered fittings seems to be to 'feel' it on, which is not too helpful for those with no experience. I believe some boat manuals give this information but mine does not, neither does the downloaded Yanmar manual, although I know this differs from the official one.

    Firstly, push the prop on without the key and mark where it reaches on the shaft, with a pencil. Then try it with the key and it should reach the same point. Take the slack up on the nut until it is finger firm on the propeller shoulder. I find around half a turn is then enough, reaching a point at which the pin can be inserted through the castellations. This depends upon thread pitch of course. Just don't overdo the force.
    Answers to some technical queries at http://coxengineering.sharepoint.com

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