Slight rust and staining around Mk10 piston base

[mr_v]

Howdy folks,

I noticed that some MK10s have stains/rust around the piston base - the LP part of the piston. Here is an example (photo credit @rsingler):

I brush this type of staining/rust as much as I can with 1000/2000 grit combo and polish with pink paste, but there is still some staining. Presuming that this is a LP part and I won't use the reg for > 50% oxygen, how much risk am I taking?

Thank you!

 

[Kupu]

As that is the ambient chamber side of the piston head, I don't see reason to think in terms of O2% risk with an unsealed ambient chamber.

 

[mr_v]

As that is the ambient chamber side of the piston head, I don't see reason to think in terms of O2% risk with an unsealed ambient chamber.

That's what I am thinking unless I am totally missing something.

I removed all the rust - a good chunk! - from the piston. Polished and put the reg together. I suspected that reducing the piston base height could lead to a decrease in IP, but I guess I removed so little that the reg is still within the range - 135 PSI with 3 shims.

This reg was a good pawnshop find. It appeared that it never saw service, so the reg body was completely intact and undamaged. However, I was surprised by the rust buildup.

 

[Kupu]

I've had good luck removing those annoying rusty stains by soaking the piston in water for several days while occasionally rubbing the stain with a cerama bryte pad. After the multi day soak treatment, the piston gets a few cycles in the ultrasonic cleaner, again with several passes of the pad.

 

[Eric Sedletzky]

You can use some citric acid to clean up that rust.
It will dissolve ferrous metal corrosion and leave all the other components of the alloy alone.

 

[Kupu]

You can use some citric acid to clean up that rust.
It will dissolve ferrous metal corrosion and leave all the other components of the alloy alone.

Thanks for the tip. I usually use a water/vinegar mix in the ultrasonic. After reading up a little on citric acid I see why you recommend it and will add that item to the tool kit.

 

[happy-diver]

I put black shims, voila, chewed out stainless gone

 

[Kupu]

Agree, my habit is to use a minimum of 1 thin shim on each end of the spring to prevent the issue.

 

[happy-diver]

Mate the black shim just to cover the dents and divots in the piston

Both ends of the spring and the piston still rust out, shims or no shims

But that sping is made from tougher stuff than me, so it wire brushes off

But you know that

 

[Kupu]

Mate the black shim just to cover the dents and divots in the piston

Both ends of the spring and the piston still rust out, shims or no shims

But that sping is made from tougher stuff than me, so it wire brushes off

But you know that

Don't give me too much credit, you may be pointing out a false assumption on my part.

Although not expecting the shims to prevent spring corrosion, my hope was that placing a plastic shim between the spring and piston head would stop the transfer of corrosion to the piston head. With the thought that over time water would still carry corrosion from the spring under the shim, I have also tried using a thin coat of molykote111 to seal the shim to piston head contact area.
But I've not had the chance to use those regulators enough to know if any of the above makes a difference.