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Mistral - To Grind, or Not to Grind; that is the question

Discussion in 'Vintage Equipment Diving' started by Scuba Lawyer, Aug 26, 2020.

  1. Scuba Lawyer

    Scuba Lawyer Manta Ray

    # of Dives: 5,000 - ∞
    Location: Laguna Beach, California
    708
    2,004
    93
    I'm overhauling a Mistral and it turns out the volcano orifice is pretty severely nicked. The HP seat looks brand new so I'm sure it's the orifice causing the leak (The guy who sold it to me off the back of the truck told me it worked fine. :) )

    I used steel wool, pencil eraser, etc... but no joy. Is it worth trying to grind / resurface the volcano orifice with a dremel or will it widen the orifice too much so the HP seat will not seal properly? In all the Mistrals I've rebuilt I guess I've been lucky, the volcano orifice has always cleaned up nicely.

    Your collective sage advice is welcome.

    7bczn7ru_t.jpg

    cc: @Sam Miller III
     
    Sam Miller III likes this.
  2. jvanostrand

    jvanostrand Nassau Grouper

    # of Dives: 1,000 - 2,499
    Location: Waterloo, Ontario, Canada
    79
    60
    18
    I remember seeing a tool designed to cut or grind a new volcano orifice. I don't recall if it came from VintageDoubleHose.com or one of his friend's sites. Or if it was somewhere else.
     
  3. runsongas

    runsongas Great White

    # of Dives: 500 - 999
    Location: California - Bay Area
    4,112
    1,812
    113
    it looks to be nicked, so you would either have to lap it down to match the depth of the nick then resurface the orifice or braze it with a silver solder to fill the nick then resurface. reaching the surface inside is going to be the real challenge.
     
  4. happy-diver

    happy-diver Skindiver Just feelin it

    # of Dives: 2,500 - 4,999
    Location: same ocean as you
    1,283
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    double sided tape some wet & dry to the end of a wooden dowel
     
    Sam Miller III likes this.
  5. axxel57

    axxel57 Solo Diver

    624
    411
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    I'm travellin', so I can't send photos, but in serious cases like that I'm using those cone Dremel Tools which are of full metal and stone like materials.
    I look for one that fits good into the orifice and turn it by hand carefully a couple of times to straighten the inner edge of the orifice. With a polishing stick from SP I try to smooth the top gland.
    It's a delicate work because the surfaces of the Dremel tools are pretty rough, the nicks at times quite deep, and sometimes the results are not completely satisfying, but mostly they are......
     
    couv and AfterDark like this.
  6. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
    9,632
    2,355
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    Put the Dremel tool down and slowly back away!
    Any power tool is too brute force for this job, it's way too easy to do more damage than you started out with . 800-1000 wet/dry sand paper on the end of a dowel is about as brute force as you want to go. A few turns of the dowel and then inspect. It usually only takes a few turns to remove enough metal to get the job done, you can switch to 1500-2000 for a final polish. The flatter you make the cone of the orifice, the harder is is to get it to seal.
     
    axxel57, couv, dead dog and 5 others like this.
  7. Scuba Lawyer

    Scuba Lawyer Manta Ray

    # of Dives: 5,000 - ∞
    Location: Laguna Beach, California
    708
    2,004
    93
    Thanks for the input guys. I'll give the wet/dry dowell approach a shot. It will either work or I'll deem the body FUBAR and look around for a replacement.
     
    Sam Miller III likes this.
  8. johndiver999

    johndiver999 Manta Ray

    # of Dives: 500 - 999
    Location: Gainesville FL
    1,217
    1,171
    113
    When you say "flat" you mean dull (or wide) as opposed to sharp or narrow? Just curious? thanks
     
  9. herman

    herman Divemaster

    # of Dives: 500 - 999
    Location: Raleigh,North Carolina
    9,632
    2,355
    113
    Hard seats have either a small radius or sharp edge. This reduces the amount of force necessary to seal the connection and allows the soft seat to take a set better/easier. In the case of a Mistral and most other USD regs, the hard seat is a dull radius. If you grind/polish it ,it becomes a wider flat surface rather than a narrower smooth radius. I have had a good bit of luck polishing down HP and LP seats with fine sand paper but you can only go so far before the "cure" is worst than the disease.

    Mark, if you decide to trash it, let me know. I have something I would like to try.
     
    dead dog, AfterDark and johndiver999 like this.
  10. Scuba Lawyer

    Scuba Lawyer Manta Ray

    # of Dives: 5,000 - ∞
    Location: Laguna Beach, California
    708
    2,004
    93
    Hi Herman,

    Well, I tried your wet/dry sandpaper dowel approach and got it down to where there was just a faint perceptible leak. Then I took off a little more and it leaks worse than before. Crap and Argh!

    Anybody have an extra Mistral body laying around?
     

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