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sitkadiver
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MR-12 Rebuild

Wed Dec 14, 2011 11:35 pm

Well, I just rebuilt my first MR-12, and I must say I'm very satisfied with the results. I could have waited to post this, since I haven't received a new 2nd stage diaphragm yet, but it should be here next week and I can post an update of some sive photos or something.

First off, I decided to rebuild this reg becuase my shop helper said it tasted bad:

Image

After I tore it apart I was a little worried that there may be more corrosion that I had counted on. The second stage was totally green and I had a hard time removing the LP seat and nut. The exhaust diaphragm was a solid, crumbly cracker of sorts and was totally gone.

Image

Once apart, however, I could see that the really bad stuff was only in the 2nd stage and the 1st stage looked almost new inside. Although there was a ton of silicon grease in it(??).

Image

Image

A soak in vinegar and a wash down and the reg looked really shiny - AND I LIKE SHINY!

Image

I put the thing back together with no major glitches, except for one - I forgot to put the o-ring on the balance chamber. I couldn't understand the free flow at first or why the IP was sooo freakin high when the adjust nut was falling out of the reg. Oh well, live and learn.....

Here's the O-ring in place:

Image

After re-assemlby and setting the IP, this reg seems to breath pretty good. I'll give it a dunk in the sea as soon as the new diaphragm arrives from Washington.

The kit Bryan sells is wonderfull, everything fits great and with the downloaded manual, this was as easy a rebuild as any other reg I've worked on.

I didn't paint the purge button on this either. I kind of like the satin metal look so I actually scrapped off the last few bits of black paint and then left it as is.

Image
I do not believe in taking unnecessary risks, but a life without risk is not worth living. - Charles Lindbergh

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Drado
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Re: MR-12 Rebuild

Thu Dec 15, 2011 3:43 am

I like the before-and-after shots of the metal components. Always fun to see these babies come back to life :D

Does your shop helper approve of the taste now? :D
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Herman
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Re: MR-12 Rebuild

Thu Dec 15, 2011 7:43 am

I have one of these second stages that I use fairly often, I really like it.

On the first stage, did you replace the oring (#6)and backup ring (#5) in the balance chamber (aka poppet retainer #3 in the manual)??
I understand these are a real bear (not really intended to be replaced) to replace.
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sitkadiver
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Re: MR-12 Rebuild

Thu Dec 15, 2011 12:20 pm

Herman wrote:I have one of these second stages that I use fairly often, I really like it.

On the first stage, did you replace the oring (#6)and backup ring (#5) in the balance chamber (aka poppet retainer #3 in the manual)??
I understand these are a real bear (not really intended to be replaced) to replace.
No, I got lazy, plus it looked very clean inside and I was thinking I should well enough alone. The poppet and o-rings are still in the kit, so I may put them in when I replace the diaphragm.

I did read here on the forum that they were a bugger to get in and out and I'm still not as confident as I should be when it comes to rebuilding regs. I'm always concerned that I might do some irrepairable damage.

Drado, my shop assistance didn't taste test the reg again, but he did run the purge button through about 100 milliion cycles and reports that it works perfectly and is one of the funniest things in the shop to play with.
I do not believe in taking unnecessary risks, but a life without risk is not worth living. - Charles Lindbergh

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Greg Barlow
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Re: MR-12 Rebuild

Thu Dec 15, 2011 4:50 pm

I am a bit surprised that the IP is stable without replacing the balance chamber O-ring. I use a Mil-Spec 70 durometer Buna-N O-ring for that application, as it is imperative that it provides a proper seal.

As far as difficult to replace, it is similar to that of replacing the -006 in the Mistral body. I have literally replaced more than a hundred of them, and have gotten the technique down pretty well. You do need to use a brass pick, as a stainless dental tool can easily scratch the inner surfaces. That, in of itself, can create a slow IP creep issue.

The HP assembly was rolled crimped after the O-ring and back-up washer (not found in original regs produced from 1968-1971) were inserted. True, the O-ring was not designed to be replaced, but it can be done with a little patience. If you would like to swap one out that has already been serviced drop me a note. I generally just ask that you send me yours so that I can pass it along to someone in the future. I ultrasonically clean the chamber, and also replace the back-up ring if it is visibly damaged.
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sitkadiver
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Re: MR-12 Rebuild

Mon Dec 19, 2011 10:33 am

Greg,

I know you're right, I need to replace the parts in the first stage. The reg was free flowing horribly when I got it, so I was interested in establishing a "baseline" of sorts for what I needed to do next. I'm new enough to the rebuild process that I tend to tear things down and put them back together a few times whilst trying to understand the what and why of the inner workings. Something that the more experienced folks are able to do once and know they're doing things correctly.

A shop in Seattle is shipping the diaphragms(I ordered 2) so I'll get this going next week sometime.
I do not believe in taking unnecessary risks, but a life without risk is not worth living. - Charles Lindbergh

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Drado
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Re: MR-12 Rebuild

Wed Apr 11, 2012 8:25 am

About to embark upon my own rebuild (as soon as my reg gets here from the US of course) but since I'm headed for the shops tomorrow, I might as well get some parts I'll be needing such as a Mares Abyss diaphragm. What size exhaust valve will I need?
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sitkadiver
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Re: MR-12 Rebuild

Wed Apr 11, 2012 11:50 am

I believe it is 26mm.... But don't quote me on that.

If you get the kit from Bryan, the exhaust valve is there. Also, I have a 2nd stage diaphragm left over, but mine is from an atomic. Let me know if you need it shipped.

Also, this is the thread I kept reviewing while my MR-12 was on it's way.

http://www.vintagedoublehose.com/forum/ ... =17&t=5321

Good luck, they're a fun project.
I do not believe in taking unnecessary risks, but a life without risk is not worth living. - Charles Lindbergh

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Drado
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Re: MR-12 Rebuild

Mon Apr 16, 2012 9:52 am

Well, I got an Abyss diaphragm and the appropriately sized exhaust valve. I also had some spare faceplates (one with my serial number) made to spruce up my reg:

Image

Now, all I need is the reg :P
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sitkadiver
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Re: MR-12 Rebuild

Wed May 23, 2012 8:47 pm

I'm having a bit of a tuning problem...

The reg doesn't seem to be breathing at an optimal level. I adjusted the levers and it went from breathing not so great, to breathing not so great at the first draw and then shoving in a ton of air if you pulled hard on it.

It's acting as if the lever gets to a point about 1/2 way through it's arc of travel and just goes wide open. It's not free flowing, so is this simply a matter of finding the sweet spot in the adjustment?

I'm starting to wonder if he Atomic diaphragm is not correct. It's the same size and everything fits, but would the Mares diaphragm be a bit different?
I do not believe in taking unnecessary risks, but a life without risk is not worth living. - Charles Lindbergh

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antique diver
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Re: MR-12 Rebuild

Thu May 24, 2012 8:36 am

sitkadiver wrote:I'm having a bit of a tuning problem...

The reg doesn't seem to be breathing at an optimal level. I adjusted the levers and it went from breathing not so great, to breathing not so great at the first draw and then shoving in a ton of air if you pulled hard on it.

It's acting as if the lever gets to a point about 1/2 way through it's arc of travel and just goes wide open. It's not free flowing, so is this simply a matter of finding the sweet spot in the adjustment?

I'm starting to wonder if he Atomic diaphragm is not correct. It's the same size and everything fits, but would the Mares diaphragm be a bit different?
You might be surprised at the difference in performance that slight diaphragm variations can make. I nearly went crazy making diaphragms for my Trieste over the past 3 years. I would suggest the correct diaphragm for starters.

It should breathe noticeably better in the water than on the bench.
The older I get the better I was.

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Drado
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Re: MR-12 Rebuild

Fri Jun 01, 2012 8:52 am

Dave, did you get your MR-12 sorted out?

When I first rebuilt my 1st MR-12 it was breathing great. I disassembled it again and reassembled it using a Mares Abyss diaphragm and now I'm also noting what I think are the same symptoms reported by you - an initial drag, followed by a slight "give" and a gush of air. Will tweak it some more to see if I can rectify it as well.

If I may bring up another thing: My 2nd MR12 is the later kind with the bulls eye pattern. After setting the lever heigh in relation to the diaphragm, I noted that the plastic purge-button carrier inside is depressing the lever a bit causing a slight free flow. Should I reduce the lever height at the expense of some degree of performance, or is there something else to this?
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Greg Barlow
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Re: MR-12 Rebuild

Fri Jun 01, 2012 2:58 pm

Yes, you will need to readjust the adjusting nut. I recommend setting the cracking effort between 1.1-1.3". If you go any lower, you will likely get an agonizing free flow while in a face down position.

That slight hesitation should not exist, as the Abyss diaprhagam is more flexible than the original design.

While you may not get the maximum hard/soft seat separation by loosening the adjustment nut, it should not be a significant issue. I do not recommend bending the lever to compensate for the difference.

Greg Barlow
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Drado
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Re: MR-12 Rebuild

Fri Jun 01, 2012 6:12 pm

Thanks! Will do that and perform a side-by-side comparison to see if I can subjectively note the difference.
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Drado
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Re: MR-12 Rebuild

Mon Jul 16, 2012 8:43 am

Okay, here's another question - this time regarding the exhaust T. I took mine off since I'm getting the regs rechromed, but have thus far been unable to get them back on. I tried boiling it, and I've tried the hair-dryer method and liquid soap method. Both instances were also supplemented by generous amounts of cuss words. I'm able to get one side on, but alas, the other side refuses to slide on. Is there a special technique, such as rotating, or something? Anything?

Conshelf exhaust Ts are a breeze in comparison to this...
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