MK10 Rebuilding Mods and Best Practices

[Timmyjane]

I rebuilt 2 units tonight. One was brand new except for about half an hour in the pool before it started blowing bubbles. I took it apart and both o rings in the piston area had shredded. To be expected I guess with 40 year old o rings. After rebuild I can't get it below 150psi. This is with the + seat and no shims. Lockup (I learned about above ) is not crisp.

I rebuilt a second unit to see the difference and it is sitting at 145 with no shims. Crisper lockup but when compared to the old MK25 there is a difference for sure.

Per the service guide it seems the piston is possibly not making a good set. I have checked both pistons with the finger nail and all is good. It suggested that the internal o ring might be pinched so I replaced it again but there was not noticeable change.

I have cycled the 2nd stage several dozen times to see what happened but not a lot of change.

Any suggestions?
Ordered some 3M polishing products just in case it turns out I need it.


PS Uploaded several new MK10 tools in the 3D printing section.
PPS. The service kits are a scam. Why in the heck don't they include all the o rings instead of just a couple and some seats. ha.

 

[p_kos]

I rebuilt 2 units tonight. One was brand new except for about half an hour in the pool before it started blowing bubbles. I took it apart and both o rings in the piston area had shredded. To be expected I guess with 40 year old o rings. After rebuild I can't get it below 150psi. This is with the + seat and no shims. Lockup (I learned about above ) is not crisp.

I rebuilt a second unit to see the difference and it is sitting at 145 with no shims. Crisper lockup but when compared to the old MK25 there is a difference for sure.

Per the service guide it seems the piston is possibly not making a good set. I have checked both pistons with the finger nail and all is good. It suggested that the internal o ring might be pinched so I replaced it again but there was not noticeable change.

I have cycled the 2nd stage several dozen times to see what happened but not a lot of change.

Any suggestions?
Ordered some 3M polishing products just in case it turns out I need it.


PS Uploaded several new MK10 tools in the 3D printing section.
PPS. The service kits are a scam. Why in the heck don't they include all the o rings instead of just a couple and some seats. ha.

Yes, the kits are only stocked with dynamic o-rings and the crush seal ring, which is BS. For the price they should include all of them down to port plug o-rings. Even though the piston passed the finger nail test you may find imperfections if viewed under magnification. Sounds like micromesh is in your future! And an inexpensive USB microscope is highly recommended.

 

[Timmyjane]

Yes, the kits are only stocked with dynamic o-rings and the crush seal ring, which is BS. For the price they should include all of them down to port plug o-rings. Even though the piston passed the finger nail test you may find imperfections if viewed under magnification. Sounds like micromesh is in your future! And an inexpensive USB microscope is highly recommended.

I thought the pistons might need the polishing but I don't get why the new one would need polishing. Perhaps when the o ring exploded a piece go caught between the knife edge and seat. I dug my microscope out. I'll pull the regs apart later today and see what I can see. The mesh isn't here but will be this afternoon if Amazon hits their delivery date. I'm starting to understand why @buddhasummer doesn't like piston regs. lol

 

[Timmyjane]

This is the only thing I can find on the new MK10s piston.

 

[Timmyjane]

Deleted and posted better video below

 

[Timmyjane]

Looks like I might need to go get the stand to this microscope and look a lot closer. Seeing some of @rsingler pics that have been posted they are a good bit closer to the knife edge.

 

[Bloody Knuckles]

This is the only thing I can find on the new MK10s piston.

It looks to me like you found your problem. Again if you have not reviewed @RSlinger's post on How to Restore a Knife Edge Piston. Start there and get yourself some micromesh otherwise as Couv once told me your just simply chasing your tail. Don't get discouraged...The journey has just begun.

 

[Timmyjane]

It looks to me like you found your problem. Again if you have not reviewed @RSlinger's post on How to Restore a Knife Edge Piston. Start there and get yourself some micromesh otherwise as Couv once told me your just simply chasing your tail. Don't get discouraged...The journey has just begun.

Probably but both regs act funny and I only see scratches on one. I am digging in a little further now. I have not found the post on how to restore a knife edged piston. I found the one for a blunt end but got sidetracked while looking for the other. I am really curious about the second piston that didnt look bad so I went on a hunt for the microscope stand instead of continuing to look for the knife edge post. I found the stand. ha.

 

[Bloody Knuckles]

How to restore a Knife Edge Piston

About four months ago, I posted a thread on How to restore a Piston Regulator that has IP creep . In probably excessive detail, we walked through how to restore a piston regulator with a blunt-end piston. Most newer pistons have switched from knife-edge pistons to blunt pistons with a cone...

scubaboard.com

 

[Timmyjane]

Closer video of older MK10 piston edge. Anyone see anything obvious to cause a poor lockup and high IP?