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  1. #1

    Top hat to drive shaft interface?

    Getting my head around the whole carbon seal set-up.

    Can someone tell me how the top hat is held captive to the drive shaft, ie, what prevents it from slipping against the shaft in order to maintain the same rotational speed as the shaft? Is it just the friction from the two inset rubber O rings?

    Also, are the bellows full of water when in use? Is this how it cools the carbon seal, just from the water filling the bellows and the inside of the carbon seal?

    So working from the pump back towards the PTO, am I right to say the ONLY points of immediate contact with the drive shaft are;

    - The pump housing / prop which starts the shaft off in a certain direction.
    - Then the top hat.
    - Then the pto itself.

    If this is so, what makes the carbon seal stay in 100% aligned contact with the top hat? Because as I see it the bellows are holding the carbon seal at arms length as it is only being held at the other end by the clamp onto the through hull. So the carbon ring just floats, there is no contact between the inner surface of the carbon seal and drive shaft?

    Would love to understand the physics of this before I start my whole alignment project.

    cheers


  2. #2
    Pete1027's Avatar
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    I'll try my best to answer this mate having just done the carbon seal, bellows boot, pto seal and engine alignment in mine. Someone else might be able to explain it better.

    Firstly the belows bellows boot or acordain boot puts so much forward pressure on the top hat that it hold's it to the drive shaft. The carbon seal and top hat will slip before the top hat does with the drive shaft.

  3. #3
    Pete1027's Avatar
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    You are correct about the points of contact re drive shaft. This is why engine alignment is such a critical thing. Bear in mind that the bellows boot being under compression from the top hat will help to keep it more in line than if it was just hanging out there at arms length add you describe. The face of the carbon ring should be the only part that touches the top hat. The inner ring is larger than the driveshaft to give some clearance so it should not touch the driveshaft... Ideally any way.

  4. #4
    Branden's Avatar
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    i am doing it as we speak, the carbon ring sits inside the bellow and is clamped down (will be the norma clamp closest to the motor) that bellow springs forward and pushes the carbon seal against the hat creating your watertight seal (ideally) The hat rides and is sealed to the driveshaft with 2 orings and is a very tight fit.

  5. #5
    OK, so things are getting slightly clearer.

    Is the shaft under where the top hat sits, slightly tapered then to get the top hat to fit so snug? If so, which end of the shaft do you slide the top hat on from? (remember, this might be obvious when the shaft is out and in front of you, but I've never seen the components in real life).

    Finally, well for now, I guess there's no fitting tolerances or measurements when building up the drive shaft assembly. The bellows will pre-determine the pressure between the carbon seal and top hat. The pump determines how far the shaft can travel backwards and the engine position (fore-aft) determines the fit of the shaft into the PTO? If the rubber end stop is on the drive shaft, should the drive shaft have any fore or aft movement at all? or should this be dialled out with the engine mounts?

    Some serious learning going on here!

  6. #6
    Branden's Avatar
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    honestly it made absolutely no sense to me either until i pulled it out and looked at it. You will clearly see where the hat and ring go as there is one spot on the tip of the driveshaft that will have a groove cut in it for the c clip and you will see the the metal hat once sprung forward towards the motor will be stopped by the c clip and it fits perfectly inside the groove of the hat (i hope that makes sense) when you put everything together you will slide the driveshaft in through the pump area just enough to poke through the bellow and then slide the hat on and go back to the pump area and slide the shaft all the way into the crank (make sure it is fully engaged into the crank) you will know if its not as the pump will not bolt up correctly. So finish bolting the pump up as it has to be to get the c clip and hat fully seated. You may have to really wrestle it back but it will go i dont know if its correct or not, but i took a dab of oil and ran my finger around the o rings on the hat to lube them up so it slid easier on the shaft.

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