A real creep!

[Eric Sedletzky]

I have a MK 20 that was creeping really bad.
It blew right past 135 and would start to slow down around 150 and finally stop (kinda) somewhere around 160.
Just to be clear, I have never personally had this reg apart, all prior work was done by professionally trained technicians at authorized service centers.

Ok, so this reg was being used as a tire inflator, to run airbrushes and paint guns, air tools, etc.
I had dismissed it as no longer suitable for diving.

So yesterday I figured it's a nice reg, this was my first reg set dammit and I want it to be right!
I had a kit saved for it, so I tore it down and decided to lap out the knife edge with some black emory rouge on a piece of T-shirt rag. I melted some of the rouge onto the cloth with a heat gun.
I spun the knife edge into the rag and shined up the edge very nicely without really changing the shape of the knife edge like micro mesh could do. Black rouge will cut and remove micro scratches but will also buff to a high shine.
I put the service kit in and low and behold, the reg locks up a very solid 132 and stays!
Wonderfull! I'm so happy!!

 

[halocline]

Eric, when you were working on it, did you notice if the piston had a brass tip, or was it all steel?

 

[Eric Sedletzky]

Eric, when you were working on it, did you notice if the piston had a brass tip, or was it all steel?

All steel.
IDK if the piston was changed at some point by the shop or not. They never said anything. I know it had the yoke nut recall done years ago.
This is the first time I've ever personally had this reg apart.

 

[Geo7]

Wow, I only know the micromesh method as published here by @rsingler. Would love to hear more about the emory stuff and maybe some pics as well...

 

[rhwestfall]

Interesting...

 

[Eric Sedletzky]

I used black emory.
I also have green which is finer, and blue is for final coloring.
The other colors are better for aluminum.
I just used an old scrap of cotton T-shirt and rubbed some of the emory on it. I had to use a heat gun to melt some onto the rag since it's wax based and melts evenly coating the fabric. I rolled up the rag into a point and stuffed it into inside of the piston shaft and twisted the piston back and forth for a few minutes.
Then did the same on the bottom edge, and finally on the outer edge. When I was done the knife edge was visibly shiny and polished. I assembled it with a new seat and full kit and it locks up better than when it was brand new. It worked so well that I would consider taking a brand new MK25 apart and giving it the same treatment even before I'd use it for the first time.
Another thought came to mind about why knife edges get scored, and my belief is that it's mostly caused by aluminum oxide in dirty aluminum tanks. Aluminum oxide is very abrasive and it's a component that's used in sandpaper. Iron oxide does not scratch the same way, it's not as sharp. And all my steel tanks are spotless anyway.
So this happened way before I was exclusively using my own tanks and was using aluminum rental tanks many years ago.

 

[Geo7]

This observation on aluminum oxide is consistent with Rob's T3 developing a mild creep during his lievaboard trip (but the reg kept working within specs)...

 

[Eric Sedletzky]

I also wanted to mention that they do make small cotton buffs in cone shapes, flat shapes, etc. that have a 3/32" shank and are used for Dremel tools.
Some rouge could be put on those and used in a controlled manner on a drill or slow moving rotating device.
I wouldn't use it on a Dremel, too fast.
Rouge is reasonably safe to use because it won't remove a lot of material, and it won't significantly change the geometry of the knife edge.
What is does is removes or averages out any sharp lines that may be on the knife edge so that you get a solid mating seal when the knife edge meets the seat with no deep groves.

 

[Nemrod]

Micromesh is great stuff for a lot of things but I also prefer (various grades) rouge for the knife edge and similar buffing of micro scratches or pitting.