MR12 Snail Shell Balance Chamber Orings

[jacked_72]

Do you guys dig out the teflon backup oring from the balance chamber or just the viton ring? I got the viton one out without difficulty, but the teflon one looks harder, plus I don't know if I can get the new one in without damaging it.

Thanks.

 

[Greg Barlow]

I have rebuilt more Voit/Swimaster MR12 regs than I care to count. I have only replaced a couple of back-up rings, as the vast majority show no visible damage under 3X magnification.

When AMF was producing the regs, the service procedure was to replace the HP balance chamber as one complete unit. When they were created in the factory, the back-up ring was installed (size -005), and then the 70 durometer Buna-N O-ring (size -006) was inserted. Next, a flat washer was placed in the chamber prior to the unit being crimped in a die.

You need to remove the O-ring using a brass pick. I find that a brass safety pin works well. Pierce the O-ring, and then carefully lever it out so that you can grap it with a brass hook. You need to be real careful not to scratch the inner surface of the chamber, as that can create IP drift that is hard to diagnose.

I use a Viton 75 durometer Mil-Spec O-ring for this specific location. They are more expensive, but what's an extra $0.50?

A modern Aqualung HP balance chamber can be machined to replace the Voit version. It allows much easier O-ring replacement, but I have never seen the need for my own personal regs. I've gotten to the point where I can remove and replace the O-ring within a few mintues. I do ultrasonically clean the housing when rebuilding the reg.

Greg Barlow

 

[jacked_72]

Thanks Greg. Just the info I needed. I used a sharpened brass rod to get out the -006 oring, but a brass safety pin is a great tip. I'm happy that I don't have to deal with that backup oring. I don't know how I could get it out and I sure think that putting the new one through that little hole would damage it. I see now that the opening is in fact a brass washer, now that you mention it. I'm glad I took this reg apart; I couldn't believe it would be something I'd want to use, but I see Conshelf and DA Aquamaster in the design. Now I'm very comfortable with it. Do you just resurface the HP seat like the DA Aqumaster seats or do you typically replace them?

Also, have you got a source for the new silicone abyss diaphragms for the second stages? The old crinkly one makes me laugh every time I breathe in. Is this a Trident part or does it only come from Mares in the proper size? I wonder if they were crinkly like that when new?

 

[herman]

You will find that pretty much all regs follow one of just a few different basic designs, many of which are based on the RAM first stage. The second stage of that reg is really a nice performer. It is what I use on several of my regs. If your second stage has the dual (2 in line) exhaust valves, most of us do not use the outter one, there is just no need. The seat can be replaced with a Conshelf/RAM seat however the pin will have to be replaced, offhand I forget which pin you use but Greg will likely come back and give you the details.


For a pick, I use a straight stainless dental pick. The use of brass picks is somewhat of an old wifes tale because they will also scratch the brass parts of a reg almost as bad as steel but without the added strength of steel. If anything they may actually be worse than steel because you may tend to be less carefull with them. Just as with any other metal, brass comes in various alloys and can be hardened. Reg body and parts brass is fairly soft, making the machining of the reg much easier and there is no need for it to be hardened. On the other hand, a pick needs to be harder material so it will not bend and needs to be hardened (heat treating process) so it will not become dull. Hard brass pick + soft brass part = scratch. The way I heard it described was imagine taking a mahogony wood pick to a balsa wood part, both are wood but you can do a lot of damage to the balsa wood with the very hard mahogony pick. Bottom line, use whatever you want, just assume it can distroy the part you are working with, reguardless of the material of either part.

 

[Greg Barlow]

The back-up ring is actually split in a diagonal fashion. You start one end into the housing, and then rotate it slowly to fully insert the entire part. Still, unless I can see damage (using a 3X magnifier) after cleaning, I don't replace them. The risk of damaging the interior of the HP balance chamber is not worth it, in my opinion. Getting the ring out of a Voit unit would be challenging to say the least.

I recommend replacing the HP poppet with either a Mares Tri-Material version, or an Aqualung Conshelf/Titan example. The advantage to using the AL is that your original HP pin is the perfect length. It should run 0.645" (+-0.003") to operate properly. The Mares requires a custom length pin. Contact Bryan at vintagedoublehose.com and order one of the AL seats. He also has a MR12 rebuild kit that contains most of the parts you need for the 1st and 2nd stage.

The 2nd stage diaphragm became "crinkly" with the passage of time. About the only ones that didn't go bad were from the late 70s, as they used a different compound. Do yourself a huge favor, and install a Mares Abyss black silicone diaphragm. You can probably get a Mares dealer to sell you one.

Greg





---------- Post added at 10:35 PM ---------- Previous post was at 10:34 PM ----------

Very good points, Herman. My "brass" picks are actually made from brazing rods, so they probably have a higher Rockwell rating than the naval brass alloys. I use stainless dental picks on many parts, but am very careful with their use.

BTW, I haven't gotten the "parts" from Rob yet. Please drop me an email to let me know how much I owe you.

Greg

 

[herman]

Ya want me to sic Barb on him??

 

[jacked_72]

I'm pretty sure the black rubber oring I dug out of my balance chamber was a -005. Did this vary during production. It wasn't hard to get mine out, but boy, getting it in the right groove was sure tough. Any techniques from the experts? Mine kept getting in the center of the back up oring. I finally wound up digging it out slowly out of the hole of the backup oring with a sharpened chopstick.

 

[Greg Barlow]

I have examples of each variation that Voit built, and they all used the -006. They are close in size to the eye, though.

Pinch the O-ring between your thumb and index finger. Insert one end down into the chamber until it bottoms out. Take a flat tool and "tuck" the remaining material into the chamber. The end closest to you will slip into the recess. Next, using your pick, slowly pull up the end that you initially inserted. Keep rotating the unit until it goes into place. It takes a few minutes to get the hang of it. More of a trial and error deal. Apply a bit of lubricant to the O-ring as well. I only use Christolube on my regs. Just make the surface shiny, no globs of lube.

Greg