MK20 Ramblings

[snowdog61]

Going through the wife's MK20 again after it started dribbling out of her 2nd after our 1st dive on the last 2 tanker. I adjusted her 2nd to get it to stop and then checked the IP - was 135 but quickly creeping to 150. Creep was slow enough that her respiratory rate would make it a non-issue for the next dive but it obviously was in need of a rebuild. Was hoping VDH would carry them but no joy. Went back through my ebay history and found the mid april 2017 purchase. Didn't quit make 24 months on the rebuild and was somewhere below 200 dives so am a bit disappointed (not sure if that was warranted but was thinking it should go a bit longer). Anyways an ebay search showed rather limited availability of mk20/25 service kits (3 sellers, 4 kits of which 3 where outside the US). I ended up getting 2x kits for $60 shipped from Hong Kong so am at least set for next time. I haven't pulled hers apart yet to see where the leak is happening - likely not going to be obvious. Hers was previously converted to the new composite piston but still has the old style cap with IP shims. I'm debating whether to convert to the MK25 style adjustable IP cap but not sure there is a need. IP was checked in January and was rock solid right where it has been for almost 2 years. Installed spring and shimpack keep it right at 135 so see no reason to change the set point. Anyone see a good reason to try and locate the 3 parts needed to go adjustable? Missing the protective plastic cap that goes over that cap too. If anyone has a spare I'd like to at least get that.

 

[rhwestfall]

Watching this.... The family "warm water travel" rigs are MK20/G250's. One of 3 needs a rebuild. All three have the new pistons in them (IIRC, or I have one piston to go in one), and this one will get the adjustable seat when it is done...

lead on my friend.....

 

[fmerkel]

All I can add is getting the IP to be solid on my wife's MK20 is a pain.
To get it solid on a MK5, MK10, MK14, and MK15 is not a problem at all.
The MK20 works great. Getting the IP stable can be obnoxious. I don't trust it to go 6 months, let alone a year.

 

[snowdog61]

Watching this.... The family "warm water travel" rigs are MK20/G250's.

Yeah that's what hers is paired with. I had a Zeagle LT (Flathead 6 non-sealed) around that I paired her 2nd with. Will say that I like the breathing characteristics of the G250 over the ZX 2nd. Venturi effect is way more noticeable on the ZX - know it was installed correctly but thinking I'll need to take a closer look at the differences in the poppets next time they are apart.

 

[rhwestfall]

I speculate that it is the sharp knife edge (or lack of in this case) in conjunction with the seat design that is the issue. Keep in mind, the MK10+ has a sloppy IP issue, and that was the predecessor to this one, keeping a bunch of the design elements. Not my favorite stage(s) at all.

 

[snowdog61]

I don't trust it to go 6 months, let alone a year.

I try and check the IP every few months. Zeagles always have had a bit of a creep (thinking o-ring movements) but always lock up after 4-5 psi. I've gotten a bit more anal on my post dive soak and after care after seeing what was happening with them under my previous rinse and store routine. I don't see a reason you shouldn't get 2yr and 200+ dives out of a service. I'll go until the IP gets out of hand. I rebuilt my 5 sets close to 2 years ago - I bounce back and forth between my Zeagles while she is exclusive to her MK20/G250. Guess I need to pay closer to the rebuilds and use. Don't remember having any issues with her rebuild - was more effort than the MK16 and Zeagle diaphragms. Looked back through my posts and do see that I posted about this reg not locking up and creeping. There were suggestions on checking the durometer of the the HP seat o-ring and piston knife edge. Guess I'll have something to look for when I pull it apart.

 

[fmerkel]

I have gone to poly HP O-ring. Haven't had it in service long enough to comment for sure but I think it's an improvement. You definitely need a high duro O-ring there. You can put in a 70, and it'll work, but it will start leaking and it may get nibbled after awhile. The gray stem shims make a difference too. I tend to re-use them but they do wear. I can get maybe 2-4 years out of a set. I don't much like that particular engineering bit and it's important to get those little things in the right order and proper orientation, which took me awhile to find out courtesy of help on this forum. The manual sucks in this regard.