axxel57
Contributor
Which Buna do you use for the 011 o-ring on the soft seat?
MK20 fresh rebuild - how much creep is normal?
- Thread starter snowdog61
- Start date
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OP
snowdog61
Contributor
Used what was provided in the SP kit so will assume it was a 70. I was also thinking o-rings but cant say piston or seat or maybe even surface finish could be holding up movement. Something has to be moving around. I'm sure it will dive just fine but it just bugs me. may be time to pull the part stackup and try and figure it out.
halocline
Contributor
I think, but I'm not sure, that the o-ring sealing the seat should be a higher duro, maybe 85. It does have a HP gradient.
Regarding the creep, if it really is creeping with a new seat after being pressurized for a few hours, with maybe 40-50 taps on the purge to break in the seat, then something is either wrong with the piston or the new seat. You can take it out and use micromesh to clean up even the most tiny little scratches or any grease or anything on the piston edge, and make sure it stays absolutely clean. Its amazing how the smallest amount of foreign matter or imperfection can result in IP creep.
Regarding the creep, if it really is creeping with a new seat after being pressurized for a few hours, with maybe 40-50 taps on the purge to break in the seat, then something is either wrong with the piston or the new seat. You can take it out and use micromesh to clean up even the most tiny little scratches or any grease or anything on the piston edge, and make sure it stays absolutely clean. Its amazing how the smallest amount of foreign matter or imperfection can result in IP creep.
OP
snowdog61
Contributor
We'll be diving this weekend so I'll throw the gauge on it when we are done and see what's what. Hoping that the issue will go away or at least diminish to just a few psi delta. If nothing else, I can pull the piston out and re-inspect. There may be some cristolube on the tip and seat from when I put the piston in.
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fmerkel
Contributor
The MK20 does need a high duro on the piston stem. Lower could leak (probably slowly), and may be subject to 'nibbling' (being slowly shredded) over time with the leak getting worse. This happens in my wife's MK20 even with the higher duro O-ring in the supplied kit. Kits are old, not sure if that's a contributing problem. They've been stored well.
I've opened up a MK 20 that likely had all original parts in it. All were in good shape. Cleaned, lubed, assembled > IP was solid and no leak. Parts had to be 15+ years old.
I've opened up a MK 20 that likely had all original parts in it. All were in good shape. Cleaned, lubed, assembled > IP was solid and no leak. Parts had to be 15+ years old.
OP
snowdog61
Contributor
again, used what was provided in the kit. If it doesn't work correctly after tomorrow i'll dig back into it. I'll grab a durometer from work and see what the actual o-ring tests out at but yes, seems it would need a bit more stiffness with a 3000+ psi delta. Don't make 'em like they used to......
fmerkel
Contributor
Don't have a durometer but I've been able to tell the harder ones with fingernail press comparison test. There may be a color mark on it but maybe this changes over the years? My kits are probably 10 years old. Got them from a shop that was going out of business.
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