MK10, MK10+, MK20...reliability

[beachnik]

For you guys that do your own maintenance, have you noticed any significant difference in reliability between:
- MK10
- MK10+ (assuming the latest HP seat version)
- MK20 (circa 1996 - hence, an early piston configuration)

Maybe instead of 'reliability' I should say 'service interval'. Do you find that you have to rebuild any one of these more often than the others?

I just got an MK20 - somewhat unintentionally. It was bundled with something else that I wanted. Thought I'd just resell it. I wasn't even looking for one, but now that I've got it - wow, it's pristine. It looks so great, I'm thinking of keeping it and selling my MK10+. But then, I'm only seeing the outsides - not the insides!

I'm starting to think that all across America there are closets full of barely used SCUBA gear. Soon to be on ebay.

Thanks

 

[cbmech2]

I have both a MK10 and MK20 and both have been serviced every year. Both have never let me down reliability wise. Not mush to go wrong on the inside since most of it is either rubber or teflon. One note of caution with the MK20 you just picked up, there is a yoke retainer update that came out a few years back. If you look at the yoke saddle, the original has three slots and the update has two.

 

[halocline]

The MK 20 had (I think) three piston types; the middle one with the brass tip is the one that I had major problems with. Once I replaced that with the newer composite piston it worked GREAT and I have a feeling that it will last longer between rebuilds than my MK10s with the knife edge piston. The first MK20 piston type I don't know about, but I know someone who does and I bet he'll chime in on this thread. My MK10s tend to creep a few PSI if they have not been used for a while, but once they've been on a few dives they lock up fine. My MK5s, OTOH, lock up perfectly every time right from the start; who knows why. Same seat, bigger piston head.

 

[DA Aquamaster]

That would be it - same seat, bigger piston head. The Mk 10 was basically the only small headed piston reg Sp ever made - not that it was problematic, the smaller headed piston just offerred very little in terms of any advantages (slightly smaller body size).

The first Mk 20 piston was stainless steel with a knife edge seating edge, the second was a stainless piston with a rounded brass seating edge. The third was the curent stainless steel and plastic head piston used on the Mk 25. As matt indicates the second piston was problematic as the lock up was a bit spongy and they tend to develop IP creep overtime that cannot be resolved with an annual service. Its no big deal as a new piston (the current Mk 25 piston) will solve it for less than $40.

The Mk 10+ used a similar rounded seating edge design and the initial Mk 10+ seats had issues with limited life. The later seats are much better and I have not observed any reliability or service life issues with mine and those that come in for service usually seem to lock up just fine if the service has been even remotely recent.

 

[drbill]

I have several Mk10's, do very minimal maintenance on them and they are far more reliable than most products I've purchased (computers, etc.). I dive them hard, deep, frequently and the only "failure" I had was two cracks in the core of the first stage. It still breathed fine, just let off a whistling noise that sounded like I was a whale. Got that replaced years ago and the unit continues to function very well. I swear by them, not at them (like my poor Dell computer).

 

[beachnik]

mattboy / DA Aquamaster...

Thanks for both your comments. That's exactly the type of info I was hoping for - a lot of great stuff there.

Here's another MK20 question...
If I've got the first piston design (which I'll confirm), is it worth keeping it as opposed to going with the 3rd design?

• This reg was last serviced in March 1997 and then put in someone's closet. That predates the 3rd piston.
• I don't know if I care about a plastic piston head in the 3rd piston design (I'm not diving in cold water, and I might not notice a performance improvement resulting from the lighter piston)
• On the other-hand, the extra o-ring on the 3rd piston design sounds like a good idea for improving reliability. Significant, if true.
• I read SP engineering bulletin 267 in which they explain they went to the SS tip for improved 'mechanical wear' - that I like. If I'm reading DA Aquamaster correctly, the first piston DID have a SS tip. Everything old is new again.

(still here?...I digress)
I started lurking in these forums and reading your posts a little over a year ago. After-which, I decided to convert (to Scubaproism).

Seriously though, I might not have asked this question about the MK20 had it not been for the experience that I had with a newly rebuilt MK10+ that I bought about a year ago. (while it must have the round edge piston, you'd think it's got the up-to-date HP seat. You'd think.). At about dive number 45, my also newly rebuilt G250 started to mildly free flow with the adjustment knob all the way out (the moment the regulator was pressurized). I called my repair guy, he said 'don't sweat it - turn the knob in'. I did another 15 dives. At dive number 60 I bought an IP gauge with an over-pressure-relief valve. The MK10+ caused the OPR valve to pop (it's set for about 200 psi). Yikes. Seems a little early for an HP seat to go bad.

 

[DA Aquamaster]

I would not replace an early stainless steel piston in a Mk 20.

----

Anytime you have a second stage problem, start the diagnostic procedure at the first stage.

 

[beachnik]

I would not replace an early stainless steel piston in a Mk 20.

----

Anytime you have a second stage problem, start the diagnostic procedure at the first stage.

DA...
Many thanks.

 

[halocline]

One thing you could do is inspect the MK20 piston edge with a jeweler's loupe. You'll see any imperfections very clearly. Last summer one the instructors at the dive shop in Roatan where I did my DM had an old MK20 that was a notorious creeper; in fact she hadn't dove with it in several years because it would eventually start flowing, usually after 30-40 dives from being rebuilt and usually pretty suddenly. I found the piston edge had several little nicks and dings that I couldn't see at all or even really feel with my fingernail. So I used some micromesh to lap sand and polish the edge (as an experiment before resorting to a new piston) and it worked great. As far as I know it's still working, I have a feeling I would have heard something otherwise.

I suspect I was a little lucky with that, but I have found that micromesh is pretty useful stuff for that and for breaking up the glaze on pistons right where the HP o-ring sits. I've cleaned up a few of those and found a big improvement in IP stability at high tank pressures. My MK5s and 10s were all running a little higher IP at full tanks, and the only thing I could think of (and Awap) was a little extrusion and friction at the HP o-ring. Polishing the piston stem and using 90 duro polyurethane o-rings really got rid of the IP rise at 3000 PSI.

 

[beachnik]

One thing you could do is inspect the MK20 piston edge with a jeweler's loupe. You'll see any imperfections very clearly. Last summer one the instructors at the dive shop in Roatan where I did my DM had an old MK20 that was a notorious creeper; in fact she hadn't dove with it in several years because it would eventually start flowing, usually after 30-40 dives from being rebuilt and usually pretty suddenly. I found the piston edge had several little nicks and dings that I couldn't see at all or even really feel with my fingernail. So I used some micromesh to lap sand and polish the edge (as an experiment before resorting to a new piston) and it worked great. As far as I know it's still working, I have a feeling I would have heard something otherwise.

I suspect I was a little lucky with that, but I have found that micromesh is pretty useful stuff for that and for breaking up the glaze on pistons right where the HP o-ring sits. I've cleaned up a few of those and found a big improvement in IP stability at high tank pressures. My MK5s and 10s were all running a little higher IP at full tanks, and the only thing I could think of (and Awap) was a little extrusion and friction at the HP o-ring. Polishing the piston stem and using 90 duro polyurethane o-rings really got rid of the IP rise at 3000 PSI.

Mattboy...
Great advice. Thanks!