Advise on my "new" MK5

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Probably the biggest challenge in rebuilding the MK5 is removing the old HP piston o-ring cleanly without scratching the journal it sits in. I wonder how many MK5s were ruined by careless techs digging out that o-ring while answering the phone. I use the scubatools double hook o-ring pick for that; it works great. I just bury the point of the pick in the old o-ring so it never comes near the metal and ease it out.

I bent a pin that came with a shirt and stuck the oring slightly. It worked like a charm and was not a challenge to remove the o-ring at all. To install a new one I used the piston bullet to push it into place, it worked well too. I was surprised how easy it went.
 
Good info so far. Re: the question about lubrication- If you mean would a PTFE grease help to raise the I.P.? No. Chances are it would actually lower the I.P. Anything that affects the piston stroke, will change the I.P. in one direction or the other. e.g. extruded o-ring, stiffer spring, shorter h.p. seat, or less effective lubricant will cause the I.P. to rise.

BTW: As this is the DIY section my vote is to rebuild it just for GP. If you decide not to, please at least perform the Usual Suspects check list. http://www.scubaboard.com/forums/regulators/346813-regulator-inspection-checklist-rev-7-a.html

Looking forward to your update.
 
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Bro couv is right: if the grease is silicon and you replace it with PTFE, the IP will go down. I reported a case here that was -11 PSI, but it was one off, and the methodology was questioned.
 
I realized that I never did let you all know the result of my MK5 rebuild. I did decide to tear it down and re-lube it. The original silicon seemed to be drying out and I am sure glad I took Hermans advise and cleaned all that off and re-lube with Christo-Lube.

The ip is 130 (using a +hp seat) and only using two shims.

I've got about 15 dives on it so far and it is beautiful paired with a totally rebuilt 109 (actually a 156 now).

Now for another question. I just purchased another brand new MK5. This one has the old style flat white hp seat. I rebuilt this one too, but didn't replace the original seat. Here's my question, are the flat (not convex) hp seats fine, or should I replace it? The ip is 125 with the flat hp seat, so I'm happy with that. Thanks
 
Here's my question, are the flat (not convex) hp seats fine, or should I replace it? The ip is 125 with the flat hp seat, so I'm happy with that. Thanks

They work fine. There are two downsides to leaving the old seat in. The first is that unless you flip it over, there is a pre-existing groove from the piston knife edge and you'll likely never get the piston to line up exactly where the old one did (even if you leave the seat in the carrier) and so you can expect a bit of creep. You might get lucky, but it's very easy to just flip the seat. The second is that the flat seats can result in a whistle as air flows by the piston edge, and overall do not flow as much air as the conical seats.
 
Now for another question. I just purchased another brand new MK5. This one has the old style flat white hp seat. I rebuilt this one too, but didn't replace the original seat. Here's my question, are the flat (not convex) hp seats fine, or should I replace it? The ip is 125 with the flat hp seat, so I'm happy with that. Thanks

I have had good luck reusing Mk5/7/10 seats (both styles) as long as I did not disturb the seat in the seat carrier. I only remove it if I plan to flip or change it. I just did a Mk7 yesterday that has had a flat HP seat for at least the last 5 years and the seat had already been flipped (probably when I did the 1st service when I got it). I replaced it with another flat seat so it should be go for another 10 years or so (just hope I can too).

I tend to set IP on the low side to give it room to grow. But those older designs will see some IP change with changes in tank pressure, especially the Mk 10 with its much smaller piston surface. They are not perfectly balanced and friction between the HP o-ring the piston stem will vary with tank pressure. So I usually shoot for 130 to 135 with a full tank which may drop to 120 to 125 when the tank is under 500 psi. But the balanced regs still seem to breath quite well at IP less than 125. So you may want to measure your IP with both a full and a low tank and see if you are satisfied.
 
Awap and Halo have mentioned not to remove the seat.....good advice. One other thing that may help is to draw an index mark on the seat carrier and regulator body so that when you re-install it, you have everything in the same position.

I agree that the white seats are just fine unless you're having some annoying groaning when you breathe in.
 
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