Mk5 Questions

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DIY Brothers,

Much to my surprise, an eBay Scubapro Mk10 transformed into a Mk5 while in the mail. In my defense, it was listed as a Mk10, and the auction pictures were a little blurry and end-on, not profile… it is in really great shape (spotless, near-new appearance)... To to my embarassment, I only discovered it was not a Mk10 when I began to tear it appart while glancing at couv's wonderful annotated Mk10 diagram (thanks couv!!)... scratched my head, then looked at couv's Mk5 diagram and went "Ah-ha"! Sheesh....

Anyway, I have some questions for the Mk5 gurus. First, please confirm that this is a Mk5 (see picture), then:

1. It appears there are variations in the seat used in the Mk5 (flat and concave), mine is a flat white “puck” type (see picture) below. Were there also different pistons for the Mk5?

2. Have any of you EVER seen the spring painted? Were they color-coded? This spring looks like it had a red stripe spray painted on…? (See picture). Or was this something the last owner did??? Strange….

Initial testing showed a good, quick lockup, no creep, but at a too-high IP of 150 psi. There are no shims.

Based on a sticker on the yolk, the reg was probably last serviced in December 2004.

3. Could the stable, but too-high IP be caused by the lube on the o-rings breaking down (the remaining lube did look pretty “goopy&#8221. I also saw red paint flecks on the piston knife edge, and suspect this might also cause it to lockup at a higher IP…

Thanks in advance for the advice.

Best wishes.

 

[redacted]

Yes, a Mk5. But a good one with heavy yoke , 5 LP ports (you can tell by the shape of the turret), 2 HP ports, and the newest version of the piston. It might even be perfect if it has a SS swivel retainerIf you really would rather have a Mk10, I'll swap one out with you as I prefer the Mk5 over the Mk10.

Mk5 and Mk10 use the same HP seats. Original was the flat (and flipable) seat. Newest version is the cave cone seats. Red dye on the springs is original and common. A good cleaning might bring IP down a bit but you might need to resort to a tall cave cone HP seat. If you are going to try to re-use that side of the seat, do not remove it from the retainer as that will probably give you more IP problems.

 

[DA Aquamaster]

DIY Brothers,

Much to my surprise, an eBay Scubapro Mk10 transformed into a Mk5 while in the mail. In my defense, it was listed as a Mk10, and the auction pictures were a little blurry and end-on, not profile… it is in really great shape (spotless, near-new appearance)... To to my embarassment, I only discovered it was not a Mk10 when I began to tear it appart while glancing at couv's wonderful annotated Mk10 diagram (thanks couv!!)... scratched my head, then looked at couv's Mk5 diagram and went "Ah-ha"! Sheesh....

Anyway, I have some questions for the Mk5 gurus. First, please confirm that this is a Mk5 (see picture), then:

1. It appears there are variations in the seat used in the Mk5 (flat and concave), mine is a flat white “puck” type (see picture) below. Were there also different pistons for the Mk5?

Yes, the original seats were flat and reversible. The later ones are grey, concave and come in 3 heights. In the middle were concave seat in various colors while SP tried to get the materials right.

There was also a change in the piston. The original Mk 5 piston had fairly small bore and was straight through out it's length. The later ones have a larger bore diameter that flares/bells out at the piston head, smoothing and improving the flow a bit. You can see the difference in IP drop with a flow test bench, but you probably won't notice it in the water. The later pistons also had more metal on the stem near the head like yours, so it should have the flared end to the air passage.

2. Have any of you EVER seen the spring painted? Were they color-coded? This spring looks like it had a red stripe spray painted on…? (See picture). Or was this something the last owner did??? Strange….

Yes, originals were unpainted but red springs are the norm on later Mk 5s and you got one of the last versions of the Mk 5. You also see red springs in properly updated Mk 15s.

Initial testing showed a good, quick lockup, no creep, but at a too-high IP of 150 psi. There are no shims.

It's common for the springs to get a bit stiffer with age. Thus the multiple seat heights in the current kits. Installing one of the two taller than standard seats will lower the IP by a maximum of about 20 psi.

Based on a sticker on the yolk, the reg was probably last serviced in December 2004.

The flat white seats were long gone by then, so if serviced then, it was done with old stock parts.

3. Could the stable, but too-high IP be caused by the lube on the o-rings breaking down (the remaining lube did look pretty “goopy”). I also saw red paint flecks on the piston knife edge, and suspect this might also cause it to lockup at a higher IP…[/QUOTE]No, its a spring/seat issue.

 

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Thanks awap and DA Aquamaster! That is exactly the info I needed.

Thanks for the offer to swap, but I was actually planning on picking up a Mk5, awap. I was just surprised with the "Mk10/R109" I was bidding on turned out to be a Mk5.

Both the Mk5 and the R109 are in near-new condition. I really lucked out, since the pictures posted on eBay were pretty blurry. The R109 had already been updated to a BA with the current S-wing poppet, and breathes really well.

I'll probably just clean and re-lube the R109, but rebuild the MK5 based on both of your advice.

Thanks again for the quick responce!

Best wishes.

Edit: The swivel retainer is chrome-plated brass (it has a couple small nicks on the head) :depressed:

 

[Zung]

Neverthe less, it'd still be an interesting experiment to clean up the old goo, apply some fresh Christo-Lube and see where the IP goes.

SP once said that using other lubricant than Christo-Lube may raise the IP by as much as 10 PSI. I'm still puzzle by this statement, and maybe dried-up Christo has the same effect.

 

[redacted]

I'd take a closer look in the body for shims. Old shim were almost clear and could be hard to see especially if there is a bunch of silicone. Worse comes to worse, I experimented with sticking shims inside the seat retainer to raise the HP seat a bit to lower IP. Worked OK with one or two shims but really bad things happened when I got carried away trying to drop IP below 100 psi.

I always like bad pictures on ebay. It lowers the price and scares away some of the bidders.

 

[LeadTurn_SD]

Neverthe less, it'd still be an interesting experiment to clean up the old goo, apply some fresh Christo-Lube and see where the IP goes.

SP once said that using other lubricant than Christo-Lube may raise the IP by as much as 10 PSI. I'm still puzzle by this statement, and maybe dried-up Christo has the same effect.

I might try that just for fun while I await the Mk5 rebuild kit.... Just giving it a real good careful Simple Green & water cleaning (leaving o-rings in place), then relube the existing o-rings with Tribolube...

My only hesitation in doing this "experiment" is that I don't want to keep installing & removing & installing the swivel bolt since it appears to be the brass model.... I'll think about it

Best wishes.

 

[LeadTurn_SD]

I'd take a closer look in the body for shims. Old shim were almost clear and could be hard to see especially if there is a bunch of silicone. Worse comes to worse, I experimented with sticking shims inside the seat retainer to raise the HP seat a bit to lower IP. Worked OK with one or two shims but really bad things happened when I got carried away trying to drop IP below 100 psi.

I always like bad pictures on ebay. It lowers the price and scares away some of the bidders.

Thanks awap. I'll peek inside the body for shims when I get home, it is possible they are there and I missed them.

I think the eBay Gods were smiling on me that day. I think only one other person bid on this Mk5/R109 Adjustable, I think it was a No Reserve auction....

I got it for $39.99. I would have been happy getting just the R109 for that, the Mk5 was icing...

Best wishes.

 

[Zung]

... My only hesitation in doing this "experiment" is that I don't want to keep installing & removing & installing the swivel bolt since it appears to be the brass model...

I don't think you need to remove it.

Edit

I mean, clean it up, replace the o-rings if required (careful with the HP one), lube it, put it back together with the old seat, take a reading, and if you don't like what you see, remove the seat retainer, flip the seat, or shim it à la awap, or replace it with a tall one that comes with the kit à la DA.

Btw, if I'm doing my math right, this is your second SP rig, right? What's next? Me I just score yet another MK20/G250.

 

[halocline]

Even if you have to take the piston out to add shims you don't need to remove the turret retainer. You just take the body apart with the spanner. You do need to check for shims; they're hard to see.

I have a tall seat I can send you if you want it. All my MK5s and 10s have low IP, so I use the shortest seats. You'll be impressed with how well the new seats lock up. While the reg is apart, take a jeweler's loupe and carefully inspect the piston knife edge for nicks. If you find one, you can clean it up with some abrasive; I've used micromesh on a round tapered stick. You have to be extremely careful, but you can get great results.

I see there's a polyurethane o-ring on the piston head. That's what I use; 70 duro for the head and 90 duro for the HP stem. If there's a glaze on the piston shaft in the area of the HP o-ring, you can carefully clean it with micromesh or some very fine abrasive. Between that, using good lubrication, and the 90 duro polyurethane o-ring, you can really cut down on the IP rise at high tank pressures.

You really lucked out, I'd take a late model MK5 in that kind of shape over a MK10 any day.