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Help with Scubapro MK10 Rebuild

Discussion in 'Repairing your own Gear' started by thayashi, Aug 14, 2019.

  1. couv

    couv Instructor, Scuba

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    Well, if my stocks don't recover soon, I'll be on your doorstep with hat in hand. :cry:
     
    rsingler likes this.
  2. couv

    couv Instructor, Scuba

    # of Dives: 1,000 - 2,499
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    I like @rsingler 's idea of the digital microscope, if for no other reason than to have one. But until you receive your's you can use a 10x magnifying glass and a Q-tip to inspect the knife edge on the piston. Drag the Q-tip over the edge and look/feel for discrepancies. I do have to admit the microscope will be handy if you need to dress the edge.

    To contact me, click on my name, go into my profile, and fumble your way around until you see something that says "start a conversation" or easier, look below any of my post and click the link, "quote in conversation."
     
  3. rhwestfall

    rhwestfall Solo Diver

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    see first step in post below... then this

    upload_2019-8-15_8-27-28.png
     
    couv likes this.
  4. rhwestfall

    rhwestfall Solo Diver

    # of Dives: 200 - 499
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    start with click here:

    upload_2019-8-15_8-29-30.png
     
  5. thayashi

    thayashi Angel Fish

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    OK - no usb cam yet, but took this picture. Not sure how micro we need to go. Can you tell from this? Thanks.

    0815191218a.jpg
     
  6. jormar1990

    jormar1990 Angel Fish

    # of Dives: 25 - 49
    Location: Kansas
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  7. halocline

    halocline Solo Diver

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    That piston looks pretty good in the photo. I also have a few NOS MK10 pistons I could sell if you need one. In fact I have a big box of parts that I co-own with awap, and since in the 3-4 years we've owned the box, we have never gotten motivated to list or sell anything from it, I'd like to offer the whole thing to some enterprising lad, (or lass) at a very reasonable price. Anyone interested, please contact me and we'll work out the details.

    Ok, now back to the thread. It is true that with MK10s, I have always encountered a small amount of creep if I try to re-install a piston/seat combination. This is why I try to get a clear picture of IP before I rebuild, and take my best guess at a seat/shim arrangement in advance so I only assemble once. If I end up with a low IP, like between 120-125 at the low end of supply pressure, I gladly live with it as the MK10 flows plenty of air even at low IP.

    So when you add a shim and re-install the piston, you are likely to get a slightly mushy lock up but it should be ok after a dive or two. If you are getting unstable IP when you try to raise it with shims, and find that maybe you can get a stable lock up around 125, but lots of drifting around and instability at 135-140, my best guess would be to try a new spring. I just happen to have a few of those in the big box of parts. I'm sure that those springs wear out eventually, and I have found that replacing them has improved the IP stability on a few MK10s.

    I've had luck cleaning up piston edges, but only if the flaws are really tiny.
     
    couv likes this.
  8. thayashi

    thayashi Angel Fish

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    Thank-you for all the input. I am not giving up and have sourced a new piston.
    My plan is to start over and install the new piston with new stem and piston head o-rings and a new seat.

    I purchased this MK10 which was leaking air through the body when I first hooked it up. I found the piston head o-ring so brittle, it almost just fell apart when I went to remove it.
    The unit had a blue seat and one shim (see pictured).

    Is assuming this set up put the regulator in spec my best starting point?
    If so, would anyone know which of the gray seats in the kit would be the best match to the blue seat? (Or how to measure them against the original seat?)
    Lastly, is there a best seating/cycling process to ensure a good piston/seat seal and lock-up?

    Thanks -


    0816191344.jpg

    0816191345.jpg
     
  9. thayashi

    thayashi Angel Fish

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    Update: New piston, seat, and piston o-rings installed. Locked at 129 psi with fast recovery each cycle.
    Thank-you to all who shared experience and insight. This was a great learning experience.

    I did get a USB microscope and the old piston did indeed have a nick in the knife edge, but really could not tell without that level of magnification...
     
    couv, Dark Wolf and rsingler like this.
  10. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

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    Just for my own edification, since I always use a microscope, in retrospect can you maybe feel the nick using the "fingernail test"?
    Nestle your fingernail in the hole at the end and rotate the piston. Is there even a hint of a "catch"? Or does it feel perfectly smooth, thus justifying your microscope expenditure, compared to the old ways of doing things?
    Maybe do the same thing with @couv 's Q-tip test? As usual, he has a more elegant way of doing things. In retrospect, does it pass this test too?
    You can help us old guys decide the best way of handling this problem in the future...
     
    couv likes this.

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