SP MK 10 PLUS: please help ID

[Zung]

This is a MK10 Plus: the edge is not supposed to be sharp - Actually, this one is sharper than the brass piston I have, roughly comparable to the composite piston of the MK20. I'll do the mattmagic as soon as I receive the Micro-Mesh, which should be next week.

 

[Zung]

Actually, Dr. awap also reported on another board: "I had a Mk10 that was behaving like that. Under the magnifying glass, I could see a small imperfection on the inner edge. I got a new piston, but just for the hell of it I touched up the dent with a piece of light emery cloth. Much to my surprise it worked and is still in service."

There is hope

 

[halocline]

It'll work. I'm not sure if micro mesh is the best abrasive for that particular piston, but if you lap sand the edge to get it completely flat, then use some abrasive to remove the scratches and clean up the outside of the edge, it will hold IP. Emory cloth might be better to start with, I really don't know. Steel is harder than brass.

Start by gluing some abrasive to a perfectly flat surface and carefully run the piston over it, edge down, trying keep the piston as straight as possible. I'd use water or oil as a lubricant.

 

[Couv]

Zung,

DIY brother, I do not have a MK10 Plus to compare to a real MK10, so tell me. Is the piston the same other than the knife edge? If so, why not do your own downgrade and put a bevel in the hard seat, replace the soft seat and seat retainer with old MK5 parts (I think I know someone who has one for sale ) and be done with it. Or do you see making this Plus work as challenge that you must accept? :cool2:

c

 

[redacted]

Zung,

DIY brother, I do not have a MK10 Plus to compare to a real MK10, so tell me. Is the piston the same other than the knife edge? If so, why not do your own downgrade and put a bevel in the hard seat, replace the soft seat and seat retainer with old MK5 parts (I think I know someone who has one for sale ) and be done with it. Or do you see making this Plus work as challenge that you must accept? :cool2:

c

It's one thing to do a DIY touch-up on a knife edge and another thing to cut a knife edge where there is not one. I'd put that in the same category as boring out a Mk5/10 to install a bushing and o-ring system like a Mk15/20/25. (I keep telling myself I don't want/need to do that.)

And yes, a Mk5 retainer could convert back to the cave cone seat and Mk10 pistons can be found but, at some point, you have to recognize that may cost more than just picking up another Mk10 on ebay. I think I would try a little cleanup on that piston's sealing surface first.

 

[Zung]

... Or do you see making this Plus work as challenge that you must accept? :cool2:c

I see this one as a guinea pig to test the mattmagic. If it works, I'll do the magic on 2 of my MK20s that have a light creep: 10 PSI, still within spec, but I have 2 others that have NO creep at all.

awap:
I already cleaned both the piston and the seat. The seat has a very light mark from the stem edge. I'm wondering if it's worth while to sacrifice a new seat to try?

I *REALLY* like the idea of boring out a MK5 to install the MK20 bushing and seat. Please keep us informed about your progress and post lots of pics

 

[redacted]

I see this one as a guinea pig to test the mattmagic. If it works, I'll do the magic on 2 of my MK20s that have a light creep: 10 PSI, still within spec, but I have 2 others that have NO creep at all.

awap:
I already cleaned both the piston and the seat. The seat has a very light mark from the stem edge. I'm wondering if it's worth while to sacrifice a new seat to try?

I *REALLY* like the idea of boring out a MK5 to install the MK20 bushing and seat. Please keep us informed about your progress and post lots of pics

I'm sorry. I mean an abrasive cleanup like Matt is suggesting. I don't think I would attack the very end of the piston except as a last resort. But a little micromesh work on the bottom mm may do the trick.

 

[Couv]

.....and we ain't even in the DIY section. I still want to know if the piston is the same length and diameter. ...Let's see, now a round tapered sharpening stone from McMaster, an old MK5 seat retainer, puck type seat so you can flip it in 5 years..... MORE POWER...AR AR AR.

 

[superstar]

You could chuck the piston in a lathe and turn the end to a knife edge, if you had a lathe.

 

[halocline]

I think the last MK10 piston I saw on ebay sold for about $25. Then you'd have to get a MK5 or 10 retainer, which probably means buying one of the older MK5s with only 2 LP ports. Shipping on both, you'd be over $50 easy. It's not worth it.

Then again, people spend $1500 on a titanium atomic...