SP MK 10 PLUS: please help ID

[halocline]

Yep, that's the piston. Buy it and your creep problems will be solved, and you'll be amazed at how fast and stable the lock up is. This is one case where new really is improved.

 

[cbmech2]

Zung, sounds to me that it may be time for a new spring in that MK20.

 

[Zung]

cbmech2:

That's an interesting point: can you elaborate?
According to SP, the spring needs to be replaced if the IP is out of range; according to DA, the spring "stiffens a bit with age".

 

[halocline]

Zung, sounds to me that it may be time for a new spring in that MK20.

Nope, it's the piston. Bet on it.

 

[Zung]

And so a piston it'll be... next episode in a couple of weeks

 

[Zung]

Nope, it's the piston. Bet on it.

mattboy, you're right as usual: it's the piston. I posted the results in my MK20 thread. The interesting part is that it's a composite piston to composite piston swap; so even the latest and greatests can go bad.

Thanks.

 

[Zung]

I finally got around to dealing with my MK10's:

• MK10 Plus #1: "downgraded" to MK10 by couv's order and with akscubaduck1's graceful help. With the + seat and 2 shims, 1 on each side of the main spring, IP is a bit low at 117 PSI, but it's rock solid, and lockup is instantanuous. I'm pretty sure I've got some more shims somewhere, but I can't find them just now. I guess I can live with that for a while, it's almost within range. Btw, has anybody managed to shim it at the seat retainer location, à la MK20? The seat o-ring should still seal, and it's a lot less work!
• MK10 Plus #2: full service done with 3rd party EDPM o-rings and a near-new SP seat recycled from the experiments with #1. The HP o-ring is a 010 Buna-N Duro 90. Even though it's still a Plus, IP locks up within 1" and stays at 133 PSI. SS piston, no shim, just the centering washer.
• MK10 Plus #3: this one is a rogue. After replacing the seat, IP still creeps to 150 PSI; it's got a SS piston too. My nephew gave it to me some years ago, I'll RMA it next time I see the guy.

Note that both #2 and #3 had a white seat before I started.

Thanks to all for your help!

 

[redacted]

The Mk10 seat retainer has a sealing o-ring so I didn't think you could shim it like a Mk20 to raise IP. But you made me curious so I just took a quick look and I suspect you could add one Mk20 shim between the seat retainer and the body to raise IP about 5 psi. If it is not going to work, it should tell you right away with a leak from the edge of the retainer.

I have slipped a homemade shim under the seat in the seat retainer to lower IP. Disturbing the seat in the seat retainer often leads to seat replacement but I marked the seat orientation before removing it and got away with it. Not something I would normally do but wanted to give it a try.

 

[Zung]

Thanks - Will try tomorrow, it's bed time over here.

 

[halocline]

I finally got around to dealing with my MK10's:

• MK10 Plus #1: "downgraded" to MK10 by couv's order and with akscubaduck1's graceful help. With the + seat and 2 shims, 1 on each side of the main spring, IP is a bit low at 117 PSI, but it's rock solid, and lockup is instantanuous. I'm pretty sure I've got some more shims somewhere, but I can't find them just now. I guess I can live with that for a while, it's almost within range. Btw, has anybody managed to shim it at the seat retainer location, à la MK20? The seat o-ring should still seal, and it's a lot less work!
• MK10 Plus #2: full service done with 3rd party EDPM o-rings and a near-new SP seat recycled from the experiments with #1. The HP o-ring is a 010 Buna-N Duro 90. Even though it's still a Plus, IP locks up within 1" and stays at 133 PSI. SS piston, no shim, just the centering washer.
• MK10 Plus #3: this one is a rogue. After replacing the seat, IP still creeps to 150 PSI; it's got a SS piston too. My nephew gave it to me some years ago, I'll RMA it next time I see the guy.

Note that both #2 and #3 had a white seat before I started.

Thanks to all for your help!

I wouldn't worry about the MK10#1 IP. It'll go up eventually, and as long as it breathes well at 117PSI, there's no real reason to run a higher IP. Plus, unless you are 100% certain your IP gauge is accurate, it may be higher. All my MK10s and MK5s have a low IP, under 130. I should check them with another IP gauge sometime, I might get a surprise!

For the #3, you might as well try lapsanding and polishing the piston. The point is to make the piston edge as absolutely smooth and even as possible. Over here we have a product called micromesh that's a set of adhesive cloths ranging from 1500 to 12000 grit; it's designed for taking scratches out of acrylic. I have had good luck using that on the brass tipped MK20 pistons. It's worth a try. If you were in the states I'd say send it to me and I'll have a whack at it just to see if it works.