DIY small inboard barings and seals

Discussion in 'Gas Engines' started by Tom 001, Jul 13, 2010.

  1. Tom 001
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    Tom 001 New Member

    Hello!
    I've had a good search of the net but more so of this site for similar threads but cannot find a definitive answer so here it go's.
    My self and my brother have built a 12 ft glue and stitched open boat, the reason for this is that we wanted to fish about 1/2 mile out in calm weather and any boat that we can beach launch (carry up and down steep shingle beach) was impossible to find as people tend to keep hold of such usefully boats(tenders, fishing, fun ect), and new was out of budget.

    Boat turned out just what we wanted, light, and stable, however the Johnson is from the 50's? and has served us well as a back up in the past but now I fear is beyond economic repaire, piston slap and small ends poss big and con as well. May try a air cooled engine swap I've seen success of that on this site.

    Any way background done! What i am trying to do is explore the possibility of fitting the boat with a small petrol engine, lightened 4 stroke horizontal, about 4-8 hp from a rotovator or mower, direct drive as it is only for steaming out and back in.

    It looked like a nice project, until I started to look at how to seal the shaft from the water, I was expecting to find lots of water proof bearings, perhaps rubber sealed bearings in a flanged housing with this is what you need printed on it! I really don't want to use the method of a stuffed cutlass.
    The only thing I can think of is half of a small car's front wheal drive hub and drive coupling, that gives me seal, big bearing that may handle thrust and drive and even cv, drive shaft and another cv. However i have no idea how water tight the external seal is on a car hub.
    Has any one any experience or ideas on what bearings to use or what may be cannibalized?

    Thanks for any help. Regards Tom
     
  2. gonzo
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    gonzo Senior Member

    You can use a standard stuffing box for sealing the shaft or one of the more expensive "dripless" seal types. It will need a thrust bearing. Petrol engines are hard to get into compliance in the UK. It will be cheaper and more efficient to get a new or at least newer outboard.
     
  3. jehardiman
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    jehardiman Senior Member

    I have used a CV joint for the propulsion shafting in a HPV submarine, and yes we used the oil seal as a pressure seal on the air-compensated gearbox, which was the pressure side (5 psi over ambient).

    The type of seal you are looking for is know as a "spring loaded lip seal", an automotive/marine outboard drive shaft seal is most likely a "Parker" type oil seal which is similiar. And, WHEN ORIENTED IN THE PROPER DIRECTION, can be used as a pressure seal on rotating shafting, ....however.... ALL seals leak to some extent (even the "dripless" bellows type face seals that Gonzo mentioned, they are not 'drip-proof", they just "drip less"); and when damaged lipped seals cannot be repaired without removing the shaft, something which is generally frowned upon when the vessel is in the water. Even in applications where a lipped seal is used for a through hull shaft, a secondary backup packing seal is fitted in good practice.

    Really now, there is nothing wrong with a packing gland shaft seal. All you need to do is loosen it when when starting out, and tighten it up when finished for the day. If it is leaking too much then tighten it down, and it can be repaired without removing the shafting, sometimes even while under way. Gland seals get a bad rap because: 1) someone is always forgetting to tighten them up as part of the boat shutdown checklist; 2) they are forgotten and never maintained (caused by 1 and leads to 3),; and 3) because they aren't maintained and lubericated properly they wear/pit the shaft.
     
  4. CDK
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    CDK retired engineer

    The car hub seal just keeps the grease in, it will do a lousy job under water.

    You can use the car parts inside your boat, but the wet side must be sealed off with a Simmer-ring in the proper direction. And the shaft that runs trough it must be non corrosive of course.
     
  5. Tom 001
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    Tom 001 New Member

    thanks starting to get it

    I see, I didn't realize that the seals had such directional usage and using such a seal in the other direction with the presence of water not grease may not work so well, just wear and bind.
    Still on the automotive track, how about a water pump from a large vehicle? correct range of rpm, stainless and ally parts, seals and bearings in the correct orientation all in one package, not the correct type of bearings to handle shaft thrust just side load from pulley, but may be able to be added just after the housing but before cv? I'll have a look at one.
    Looks like I may have to make my own set up perhaps using seals designed for a outboard, they must be double acting or have two opposing.
    Thanks for the hepl, Tom
     
  6. CDK
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    CDK retired engineer

    A water pump isn't a bad idea, but are you sure you can find one with a stainless shaft?
     
  7. Tom 001
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    Tom 001 New Member

    Hum I'm not to sure they must be stainless, hardened or coated as one side is in continues contact with water, mind the anti freze has additives to help stop corrosion and salt water speeds it up some what.
    I suppose it depends if the shaft is stepped, has a flange or clip inside the bearing housing, to if it can be easily replaced with a stainless of my choosing.
    That may be a better option if the original shaft is the same diameter through the seals and bearings I'd be able to use one solid shaft that wont need a special prop adapter or much heavy machining and it will be the correct length, the thrust bearing out side the housing however will have to stop the shaft slip because the others will no-longer be fixed to the shaft at all, which is probably for the best.
    Well I'll have to have a look inside one, I'm thinking the modern pumps are sealed units, got a day off tomorrow so will find a used pump that I want to use, dissect it, then get a new one for the boat.
    please post if you have more ideas or input thanks
     

  8. jehardiman
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    jehardiman Senior Member

    Automotive water pumps tend to use spring loaded face seals rather than lip seals due to tempertaure, pressure, and assembly considerations (i.e. pressed on impeller on one end and pulley on the other). You can go to Free Patents Online and search for "water pump seal" or "shaft seal" to get some idea of the different types out there.
     
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