Stuck MK10 Piston cap (Scubapro)

[halocline]

Also and here’s a BIG QUESTION: on the MK5 Piston, I noted what felt like stamped letters on the piston shaft. On closer examination, I see rough spots on the piston shaft, small scratches basically. Right about where the piston shaft passes through the little o-ring. Maybe these can be polished out, or maybe I need a new piston?.....

Also, just for fun, I installed the MK10 Yoke on the MK5, and it appears to fit okay. Any comments or feedback are appreciated.

I've had good luck with micromesh cleaning up the edge of the piston to cure IP creep, and knocking off a glaze on the shaft that sometimes appears in the area of the HP o-ring. But I've never removed visible scratches from that area. If yours is really scratched, you are probably looking for a new piston, which as DA pointed out, means a new MK5. Plus, the only way scratches could get on that part of the piston (I think) is by poor handling by a tech, and if that's the case, it's certainly possible that there are also scratches in the HP o-ring journal. That, unfortunately, means "this is the end, mate" for a MK5. So you might be best off just replacing it and benefitting from the experience of taking it apart.

As far as the yoke goes, the MK10 yoke itself will certainly work, but not the yoke retaining bolt. That must be from a MK5; they're unique I believe. Actually, I think awap has rigged up a few MK5s with the SP universal DIN retainer using some SS washers, but that might be a "don't try this at home" sort of thing.

As far as the microns of depth for various grades of micromesh and whatever the parker catalog might say, I'll claim both ignorance and apathy by saying I don't know and I don't care. I'm not trying to say I have the absolute answer, I'm just saying that I personally would not put visible scratches, especially ones the size made by 400 grit emory cloth, in a piston shaft.

 

[Zung]

... Plus, the only way scratches could get on that part of the piston (I think) is by poor handling by a tech, and if that's the case, it's certainly possible that there are also scratches in the HP o-ring journal...

I can imagine another way: sand and/or dirt enter through the ambient ports, down the body, pile up on top of the HP o-ring and scratch up the upper part of the shaft and the grove. That's also a good opportunity to damage the inside of the cap where the crown rides. I've got one MK20 just like that, even though the previous owner said it had only 150 dives; the inside of the crown is brass only, but it still works, no leak.

 

[Manow]

I know a little about micromesh; used some really fine stuff to touch up glass on some "things." It works well on glass, but it won't help this MK5. :depressed: I didn't have a dime invested in this MK5, so I'm not gonna cry. The Mk was a learning project. I think I'm going to focus on getting the MK10 in service next month. I picked up a G200B on ebay. I paid a bit much at $45.00, but it looks real clean, and I think it will be a good match for the MK10. How many complete regs can one guy own anyway.

 

[halocline]

$45 is a good price for a G200B, which IMO is an underrated regulator. Its exactly the same as the G250 except it is not adjustable. If you can find a decent price on an air barrel and adjuster knob, you could convert it.

How many complete regs can one guy own? That's a good one.....

 

[Zung]

I'd say 4 for each family memeber is fine.

 

[Manow]

Yes, upgrading the G200B to a G250 would be nice, but considering the cost of the new parts, I might be better off just buying a G250, and selling the G200B. I'll probably just use the G200B “as is" and see how I like it. Matched with the re-built MK10, I'm sure it will be a good kit. As far as the number of Regs one guy can own, I was able to rationalize the MK25/s600 as my main kit, with the MK2/R390 as my back-up. The MK10/G200B is my project-learning to work-on Regs. Kit. Those 108s and that beat up MK5 are likewise learning tools. The 108s have nice exhaust Ts, and the chrome isn’t too bad on one of them. The diaphragms are in really poor shape (dry rot), and I’m not sure which re-build kit would work best on them. Also, the 108s are not exactly the same. What I mean by that is when I remove LP hose from the 108, I’ve noticed that one 108 is pretty much open, and the other 108 has what appears to be a slot type adjustment. Now again, forgive my ignorance, but I’m still searching for schematics for the 108. I picked up the 108s because they were cheap, and the chrome & brass has a certain coolness factor. Thanks again to the experienced pros that help out guys like me. I would never consider studying vintage (discontinued) gear had it not been for this web-site, and the accurate information, encouragement and positive feedback you guys provide. Thank you again.

 

[redacted]

I'd say 4 for each family memeber is fine.

Plus spares.

 

[Couv]

I'm a bit confused. According to the Parker Handbook, Section V, Dynamic O-Ring Sealing, Paragraph 5.3, Surface Finished: "The most desirable surface roughness value is from 10 to 20 micro-inches." That's roughly .25 to .50 micro-meters, or microns.

Now the highest graded Micro-Mesh is 8000, equivalent to 3 "Micron" according to the conversion chart here. That gives "scratches" that are nearly invisible to the naked eyes, and way finer than a 400 grits sand paper.

Something's wrong, there's a discrepancy that's 2 orders of magnitude, please educate me.

Brother Zung, et al,

Perhaps it is I who needs to be educated-far be it from me to tell you to go against the Parker manual when installing o-rings in your regulators. However, I will tell you where I'm coming from with idea to cross hatch the piston stem. When a hydraulic cylinder, such as a brake master or a piston type hydraulic accumulator (very similar to a piston regulator) is rebuilt, honing is an important part of the process.

The grit used is much more coarse than the grit in a polishing kit. What you're trying to achieve is a pattern that will retain as much lubricant as possible so the stem is actually floating on a thin layer of lubricant rather than a dry stem pushing through an o-ring.

It might take a bit more research to show exactly what I mean, but look at the last minute of this vid. How to hone the Cylinder - YouTube The stones on that hone are certainly not a grit one would find in a polishing kit. I use 400 grit crocus cloth or wet sand paper.

This is just my opinion-I could be wrong.

Couv

 

[redacted]

Brother Zung, et al,

Perhaps it is I who needs to be educated-far be it from me to tell you to go against the Parker manual when installing o-rings in your regulators. However, I will tell you where I'm coming from with idea to cross hatch the piston stem. When a hydraulic cylinder, such as a brake master or a piston type hydraulic accumulator (very similar to a piston regulator) is rebuilt, honing is an important part of the process.

The grit used is much more coarse than the grit in a polishing kit. What you're trying to achieve is a pattern that will retain as much lubricant as possible so the stem is actually floating on a thin layer of lubricant rather than a dry stem pushing through an o-ring.

It might take a bit more research to show exactly what I mean, but look at the last minute of this vid. How to hone the Cylinder - YouTube The stones on that hone are certainly not a grit one would find in a polishing kit. I use 400 grit crocus cloth or wet sand paper.

This is just my opinion-I could be wrong.

Couv

The difference might be that things like brake and engine pistons have a constantly renewed supply of fluid lubricant that recoats the sealing surfaces which is not the case with a regulator where the lube is more like a grease

 

[ams511]

You will probably be better off looking for desirable models like this: eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

I clicked on the link and got, "You have been outbid", lol. Maybe we should coordinate our bidding as not to run up the prices.