Help with Scubapro MK10 Rebuild

[thayashi]

I am having trouble getting a stable IP from my Scubapro MK10. Standard rebuild and the IP locked up upon first testing. Went add a shim to increase IP but after putting it back together, it would not hold IP would creep. Checked seat and piston knife edge and everything appeared to be OK. The kit came with additional seats, (though of differing height), so I tried another one which I thought would increase IP on it's own. IP locked up, but still a little low at 500 PSI, so went to add a shim, and now it does not hold IP. I am thinking there may be an imperfection on the knife edge that "cuts" into the seat for the first time - when the orientation is changed, it becomes the source of a leak. Any thoughts, or should I try to find a new piston?

Thanks in advance,

 

[Couv]

Hi @thayashi ,

You are on the right track. It sounds like you had it right the first time, but the IP was low-you added a shim and induced a bit of creep. One thing to remember when removing or installing a shim is to return the seat to exactly the same position. First of all, unless you're going to replace the seat, do not remove it from the seat carrier. Next, it should not be necessary as the seat retainer "should" return to the exact same position when it bottoms out-but just to make sure, put an index mark on the seat carrier that extends to the regulator body. The index marks must be lined up when you reinstall the carrier.

The three seats in your kit could have saved you some of this grief. Again, you are correct in that they are an easy way to change the IP. But which one to use? Contrary to what some have written here, and contrary to even what some ScubaPro documents state, here is the order.
The + is the shortest and results in the highest IP.
Next shortest is the one marked with - l
Last, longest, and lowest IP is the seat with - ll

What? SP is wrong? Don't believe me? Have a look at this picture:

Each graduation is worth 4-5 psi IP change ~ the same as a shim.

Now all of the above may not mean diddly squat so before you go any further, please answer the following.
Did you cycle the regulator 30 plus times?
How low was the IP at 500psi? (over 125 psi, leave it alone unless there's something else out of tolerance)

So where does that leave us? If you've done the above with no help, remove the seat carrier (remember to index mark it with a Sharpie.) Take a pencil erasure and clean the piston knife edge and seat. Blow out any debris and reassemble. Test again and get back to us.

 

[thayashi]

Rookie mistake. Did not know you need to realign everything when putting in shims. I guess you would have to mark the piston orientation as well?
Or, does the piston move when you screw main housing to the main housing cap?

I used the "+" seat as it most closely match the height of the green seat originally installed. At 500 psi my IP locked at 117.
Added 2 shims but after assembly had the significant creep. Cycled more than 30 times.

Next, tried the " - I" seat - but did not add any shims. Yes, I read/thought IP would increase with the taller seat. IP was even lower.
Added 3 shims to see if I could get to spec - but creeping again.

All I have left is the "-II" seat which will not get me to spec...even with spacers.
I do have the original green seat as well.

Seems to me the I should try the "'-1" seat with a shim cleaning with the eraser as you suggest. Thank-you, and stay tuned.

 

[thayashi]

Rookie mistake. Did not know you need to realign everything when putting in shims. I guess you would have to mark the piston orientation as well?
Or, does the piston move when you screw main housing to the main housing cap?

I used the "+" seat as it most closely match the height of the green seat originally installed. At 500 psi my IP locked at 117.
Added 2 shims but after assembly had the significant creep. Cycled more than 30 times.

Next, tried the " - I" seat - but did not add any shims. Yes, I read/thought IP would increase with the taller seat. IP was even lower.
Added 3 shims to see if I could get to spec - but creeping again.

All I have left is the "-II" seat which will not get me to spec...even with spacers.
I do have the original green seat as well.

Seems to me the I should try the "'-1" seat with a shim cleaning with the eraser as you suggest. Thank-you, and stay tuned.

Sorry - "+1" seat....

 

[Couv]

Sorry - "+1" seat....

If you're using the gray ScubaPro seats, "+" is the designation.

Re aligning the piston-I would be very surprised if you could do that. I've tried by removing the 5th low pressure port cap (the one on the end) and inserted a wooden dowel thin enough to pass through the turret retainer-but I cannot be sure I prevented rotation.

If you're still having creeping issues after getting the IP low/high correct, you may be able to dress the piston.
Search for Matt Magic in @halocline 's post, or piston refurbishing in @rsingler 's post.

If you don't want to try that, I have pistons for sale......but this is the DIY forum.

 

[thayashi]

OK....cleaned up seat "+1" seat and piston - 2 spacers - would not hold pressure - kept rising over 150 before I purged and turned off air.
Tried again with same result.
Inspection of seats showed that the least piston markings was the original green seat which came in the unit. Regulator was purchased of E-Bay
looking almost new. (circa 1987 with metal yoke knob). Body was leaking air and I found the piston end o-ring hard and brittle which was replaced as part of rebuild.)
Re-installed the original seat with one spacer as it came to me, and now after 30 cycles, recovers to 130 psi quickly then drifts slowly to 136-138 (10-12 seconds).
Appears to lock at 136-138 - been sitting for over 25 minutes with no change - 2 time in a row. Tank pressure during testing 2000-2500 psi.
I will continue to cycle a few more times, but would appreciate opinions on what to do next....

Thanks!

 

[Couv]

Yes, more cycling-be like Lance Armstrong. If no joy and you've convicted the piston, perhaps you can dress it.

You'll have to modify this technique as you have a sharp piston (unless you have a MK10 Plus which would mean we have been chasing our tails)....but you'll get the idea:
How to restore a Piston Regulator that has IP creep

Here's another thread, skip to the bottom for the MK10
Dressing a metal orifice

I forgot to ask, did you replace the piston stem o-ring hidden in the body?
Did you use a piston bullet every time you installed the piston?

 

[rsingler]

Check Amazon for a cheap USB camera, and inspect the piston knife edge and the shaft of the piston under 30x magnification. That will tell you what you need to do next.

 

[thayashi]

Yes - brass/plastic/wood picks to remove o-ring. Used o-ring insertion tool and then bullet tool throughout.
Turning air off and then back on produces unstable IP. Will have to get a very close look at the piston knife edge.
How to I get in touch if I need a new piston? - not sure how messaging works here.

Anyway THANK-YOU for your help and insight. I have another MK10/G250 set up that I have serviced and everything has been by the book.
(And, two more that will need servicing in the future!) Have Harlow and Wolfinger and purchased from Herman and VDH, but I also have to admit I have
been here on the board a lot.... and you two have always been super helpful to the DIY community....

Tad

 

[rsingler]

90% chance you don't need a new piston.
Sorry, @couv ! I just HATE cheating you out of a sale.