SP MK 10 PLUS: please help ID

[halocline]

I've been asking around but nobody knows about micromesh around here. awap told me about Brasso, and I managed to find a local equivalent; while it works something wonderful on brass, stainless steel seems to ignore it completely. I made a 5' attemp on a MK20 piston shaft, but it made no difference at all. Should I try longer?

First thing would be to inspect the edge with a jeweler's loupe or other magnifying glass, at least 10X. I bet you see some scratches. Then use some silicone carbide paper maybe 400 grit, wet sanding. You can start by flattening the edge, just until there's a mark from the paper all the way around the circular edge. You'd want to glue the paper to a completely flat surface like a piece of glass, and lightly run the piston over it. Then you could try a much finer grit, like 1200, and wrap it around the edge or just use your thumb, to remove the mark left by the 400 paper and get the scratches out. You could finish with brasso or some sort of metal polish.

I would only try this if you're more or less convinced that the piston is un-usable as it is. You have nothing to lose at that point anyway.

 

[Zung]

mattboy, please enlighten me with some details; you once said:

... I have used this on 2 different MK20 piston edges to stop IP creep, and it worked great both times...

Does it mean that:

1. Before you did it, the IP crept out of range, like 150-ish or worse, and after you're through, it dropped back to 130-ish?
2. Do you remember if the recovery of the IP was faster after you're done, like within seconds? Should be, because you don't have to wait for the creep, right?

If you confirm with 2 "yes", I'll try your magic for sure, at least the modified version with sand paper. I still have this brass piston for the MK10 Plus, the one that started this thread. It's a known POS and a great candidate for sacrifice.

 

[halocline]

When I sanded/polished the MK20 pistons, it got rid of the creep. In this design of regulator, the only thing that can cause IP creep is a bad piston/seat seal. If you have new seats and it creeps, the only solution is to resurface or replace the piston. It's not a five minute job; you have to be really careful, find the right abrasive, and use magnifying glasses to really inspect it, but it should work. It's not very complicated.

I can't remember how badly the MK20s creeped, but I suspect it doesn't really matter. IMO, anything more than a few PSI over a few seconds is unacceptable, at least I wouldn't dive with it.

Maybe you could refresh our memory; at what IP does this reg begin to lock up, then how far does it creep in how much time? If it starts around 130 and then creeps to 150 or higher in less than a minute, to me that's pretty severe and I'd be surprised if you couldn't see or feel something on the piston edge, especially with magnification. Maybe the MK10+ seats are lousy; although if I'm not mistaken they're the same seats as the MK20/25, and those regs with a new seat and good piston are pretty lock solid. I have a friend who has a MK25 that locks up perfectly and it's been at least 4 years since it was rebuilt. The MK20 that I eventually replaced the piston on is just like that; immediate and solid lock up and I think it's been a couple of years since I rebuilt it.

If you want to send me the piston I'll try to work on it, but I would think you could do just as well on your own, maybe better, and there have got to be all sorts of very precise craftsmen there in the watch/jewelry business that could help find the right abrasive.

 

[Zung]

Here are the details on the MK10 Plus #3:
Purge: 110 PSI
Recovery: 125
5 min.: 139
10 min.: 142
15 min.: 146
And it tops at 152

I appreciate your offer, but as you said, I'd better work on the technique myself. I have the perfect victim to start with, the original brass piston. And if it works out allright, I can hope to improve my MK20 #3 and 4.

Thanks

 

[halocline]

It's got to be a tiny scratch; that's pretty slow creep. I'm 90% certain this will fix it.

 

[Texfrazer]

Hey Zung,

I'm going to get some Micromesh this coming week/weekend. Would you like me to grab some for you and send it over?

 

[Zung]

Oh yes, please!
I'll PM you my address and I'll reimburse you. Thank you for the offer!

mattboy, what would be the 2 grades you'd get? 1500 & 3600 grit or 2400 & 3600 grit?

If this works, it'll be a great service to the community, because we'll no longer throw the pistons away at 40 bucks a pop. Maybe I'm just a magnet for trouble, but so far, I've had 3 out of 4 MK20's and 2 out of 3 MK10's that have problems with the piston, 3 severe requiring replacement, and 2 mild.

 

[Zung]

It's got to be a tiny scratch; that's pretty slow creep. I'm 90% certain this will fix it.

It's good to know that the longer it takes, the less bad it is

 

[halocline]

mattboy, what would be the 2 grades you'd get? 1500 & 3600 grit or 2400 & 3600 grit?

It depends on the size of the scratch. That's why the magnifying glass or loupe is important. First thing, find the scratches. Then use a grit that gets rid of them, then progressively finer grits. The micromesh starts at 1500 (I think) and then goes 1800, 2400, 3200, 3600, 4000, 6000, 8000, 12000. That's for acrylic though, much softer. This is brass, so 1500 alone might work fine, or 1500, 2400, you'll have to experiment. I've alos had some luck with plain old 400/600 silicone carbide paper, wetsanding. The micromesh is better quality, but you're not looking for shine, just no scratches of any depth.

 

[Zung]

Hey Zung,

I'm going to get some Micromesh this coming week/weekend. Would you like me to grab some for you and send it over?

Texfrazer,

If you've not gotten them yet, please don't bother; if you already have them, I'm still in of course!

My bad: actually Micro-Mesh is all over eBay, and the price is very reasonable, kind of like 12 bucks shipped for 1 each of the 9 available grits at 6"x4", from the UK.