MK200 Piston vs MK2

[Hethen57]

I've rebuilt my MK2 with the service kit from Vintage Double Hose to learn on something that wasn't valuable and it came out great and holds perfect IP, it is just limited by the number of LP ports. I just received a MK200 that appears to have piston blow-by in my bench testing and was wondering if anyone knew if those pistons use the same O-ring. Worst case i can take apart my MK2 and measure, but was just wondering if anyone on here knows before I pull that reg apart? Thanks.

 

[Hethen57]

I think I answered my own question by doing a little digging in older posts. It looks like the MK200 has a slightly larger piston and takes an 023 - 70 duro o-ring, if I'm not mistaken. When I tested it on my tank, the air just seemed to flow out the ambient air holes at the end and did not pressurize my IP gauge. I have the Harlow book and I will review to see whether this points to the HP seat or the piston o-ring(s). Any suggestions or advice from the experts would be appreciated.

 

[fmerkel]

It's just about to be one of those. You know how easy it is to overhaul. Open it up and take a look. Nothing to lose.

 

[Hethen57]

Will do...and add it to the other regs in plastic totes waiting for various parts from VDH... ha ha.

 

[herman]

Def not the seat. Any air blowing out the ambient holes is a defective piston stem and/or head oring. It could also be the sealing surfaces but that is less likely unless the reg has been abuse. The seat will cause IP issues but until you get some IP, you won't know it it's good (which is likely). Also, those seats can be flipped over and the other side used if it's defective

 

[Couv]

You are correct, the piston head o-ring size for a MK 200 is a -023
Chances are the last time it was rebuilt the tech used a PU o-ring that has become a crispy critter by now, and the source of your bubbles.

BTW the stem o-ring is a -008 same as the MK 2

 

[Hethen57]

Thanks for the input herman, and couv you were spot on, when I pulled it apart that piston o-ring was very crispy, but everything else looked pristine, for something that has probably sat for probably 10 or 20 years. I will give everything a good cleaning, install new o-rings, maybe flip the seat or get a new one, and see how it functions after that. This reg was just thrown in as junk because I wanted the heavy yoke with a MK 5 that I picked up, but I guess I am just a compulsive fixer/restorer. Once you have a small supply of parts and tools, why not, right?

 

[Couv]

NP Mike.
Before you flip the seat clean and replace everything else. The seat may be good just as it is and you'll want to save the unused side for the next rebuild 20 years from now.

I probably have a heavy yoke and screw avail if you're interested.

 

[Hethen57]

Thanks couv... that is good advice! I wish I would have hit you up for the yoke first, it would have kept my life simple and I would have 2 less old Scubapro regs calling me to the work bench. I only bought the MK5 for its yoke for about the price of a yoke and it turned out to be a nicer, newer, SPEC MK5 than the one I had (and he threw in the non-op MK200 that I am working on) so my old MK5 now looks and works great and can keep the light yoke, because I have new projects with heavy yokes. Is there a 12 step group for this hobby? It all started with some gorgeous chrome Conshelf 1st and 2nd stages that someone tossed into a scuba tank purchase and I was hooked.

Regarding my SPEC MK5, I saw an old post that said you need to use heavier silicone for packing. Do you know of a good source for this? If one is meticulous with cleaning regs after each dive, and not diving in silty conditions, is such packing even necessary?

 

[Couv]

If one is meticulous with cleaning regs after each dive, and not diving in silty conditions, is such packing even necessary?

No packing necessary given the conditions above.

I prefer Dow Corning 111 for regulators that have lost some of the chrome internally.
Here is a link to a vendor, you might do a search and find a better deal.
Dow Corning -Molykote 111 Valve Lubricant 5oz | DC-111