Velvet 71C assembly

Discussion in 'Inboards' started by FBadger, Feb 24, 2018.

  1. FBadger
    Joined: Feb 2018
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    Location: Toronto Canada

    FBadger New Member

    I have a Shamrock20 ('84). I came with a 71C Velvet drive attached to a Ford 302. Motors completely rebuilt (now) and I've turned my attention to the trannie. Nice bit of engineering that Velvet drive.
    I originally replaced the seals and gaskets as I thought only and oil leak needed mending. Since, I've decided to replace the plates as the drive, in neutral, had quite a bit of grab suggesting the friction plates were warped.
    Back to my question. When I replaced the seals, originally, I tested the drive by hooking a drill to the input shaft and spun it at 1,100 rpm. I noticed there was a leak in one (top) of the bolts that holds the oil pump casing to the trannie. The bolts and bolt holes are inside the pump housing large rubber seal. There doesn't seem to be any gasket or O rings preventing oil from escaping thru the bolt holes and the pressurized part of the pump. I was actually surprised all the bolt holes didn't leak oil.
    The schematic of the unit shows no seals of any kind on the bolts or a gasket, other than the 6" ring seal on the pump housing.
    How does the oil not spew out of these holes, especially with an oil pressure in the hundreds? What am I missing???

    Thanks

    Jack (FBadger)
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I usually put soft gasket sealer in the threads.
     
  3. FBadger
    Joined: Feb 2018
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    FBadger New Member

    I suspect I will do the same on the shoulder of the bolts. It just seems very odd for there not to be some kind of mechanical seal. I'm sure there was a good reason at the time of design. Again, of the four bolts/bolt holes, only one leaked.
    I remember you advised someone about the velvet rebuild to make sure the reverse piston was fully seated before installing plates. It was suggested there was a method to install plates so they were adjusted correctly. I'm sure I'm bastardizing your advise. I downloaded the manual for the 71C and of course the one page that speaks to installing the reverse plates was missing. From what I can see, there is no adjustment with the reverse plates. You put them in and the final steel plate should be flush with the casing.
     
  4. gonzo
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    gonzo Senior Member

    There are several thicknesses on the bottom ring that are used to adjust the backlash on the plates/clutches.
     
  5. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    For sealing the threads you should use Loctite thread sealer. It's intended for exactly that purpose and works well. For disassembly. a heat gun will soften it and you'll be able to remove the bolts with no issues. Don't use a silicone, the oil will dissolve it eventually. Non=hardening gasket sealers are a crap shoot if the pressure gets too high they eventually leak. If the pressure isn't too high they hold, but you never really know. Non-hardening gasket sealers are really intended to help a gasket seal, but aren't intended to hold back any pressure. If you add any real pressure you're just asking for a leak.
     
  6. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Which Loctite product do you use?
     
  7. FBadger
    Joined: Feb 2018
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    Location: Toronto Canada

    FBadger New Member

    The leak is not through the thread but rather through the housing bolt hole and the head of the bolt. It’s like a copper wash or other should have been used to seal the bolt head to the pump housing. Very odd!
    So here is the housing with the oil pump body (below). The four mounting 5/16 bolts are inside the big o ring. The pump housing sits flush to the tranny housing plate. Oil squeezes thru the pump housing bolt hole (where the screwdriver points) and out. Was thinking of a crushable Copper washer to seal.
     
  8. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I have rebuilt dozens of them and never had a problem with soft gasket sealer. I usually use Permatex No.2
     
  9. FBadger
    Joined: Feb 2018
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    FBadger New Member

    Evening. So there is one last part I need to complete the trannie rebuild. It is the drive shaft snap ring. Its the ring adjacent to the main bearing on the intake shaft. I can't find a replacement. I can find one for 72c trrannie but not the 71C. The thing looks the same but of course there are no dimensions for the snap ring. You think it would fit?
     
  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    As far as I know there are the same.
     

  11. sdowney717
    Joined: Nov 2010
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    Location: Newport News VA

    sdowney717 Senior Member

    When I tore apart one of my 72c, I did not seal up the bolts unless the manual told me to do that.
    Had no leaks after the repair. It is a very simple transmission inside. My leak was not caused by failed parts, I had rust forming on a steel plates that opened up one of the large square seal rings, so a slow drip. Cleaning surface down with a razor blade solved that. I did replace all the seal and clutches and steels. But saved them all. There was zero wear on the clutches. Now my other 72c 10 years later is developing a very slow leak, and it need to be torn down. And I have enough parts to do it, just my time is needed.

    Velvet Drive 71C and 72C Marine Transmission Assembly (Current Production) | PerfProTech.com https://www.perfprotech.com/blog/velvet-drive/velvet-drive-71c-and-72c-marine-transmission-assembly-current-production
     
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