CMI Diablo Cup Seal Question

[ekloot]

Hi, I have a CMI Diablo Pump paintball gun from the late 90s that I'm trying to get working again. The gun has started leaking air and when disassembling the valve area, I noticed that whatever type of gasket or sealing material was originally in the metal cup seal is now crumbling away. I attached pictures and the last one shows the inside of the cup seal and the remaining seal material. Doesn't look like it was an oring, but maybe some sort of gasketing material? Is there some sort of gasket sealant type of stuff I should apply in there to replace the stuff that has crumbled away or is there some kind of actual seal or gasket that I should buy that just fits in there? Anyone know what was originally in there and what I should do?

[DocsMachine]

What you had was a disc of polyurethane, and what happened was what we call "seal rot". There's two general kinds of polyurethane, and the cheaper of the two reacts with moisture in the air and eventually depolymerizes. Or rather, it disintegrates or turns to goo.

This usually takes many years, so most companies will save a few pennies per unit with the cheap stuff. Who expected somebody would still be using a budget-priced CMI pump over 20 years later?

But, that means we're seeing more and more older guns suffer from it.

I'm not aware of any goop you can pour in there to fix it- and trust me, I've seen lots of attempts. Your best bet is to either have somebody punch a fresh disc of poly and see if it can't be fitted in there. I could do it, but I'd need the body of the cup seal to properly fit it to.

Or, hit up either CCI or LAPCO for a replacement cup seal. You'll need to know the thread on the end of the power tube (it's either 6-32 or 8-32) but generally speaking, there's a good chance any Nelson-based cup seal with the right thread will fit.

Doc.

[ekloot]

Thank you so much for the info and the quick response! And yeah, this is quite a goofy project I've undertaken getting this old gun to work haha. I used it a lot during college in the 90s to play at a local field and wanted to fix it up for nostagia's sake. After reading your reply, I went to the phantomonline website where they sell all the parts for the CCI phantom and saw they sell a cup and cupseal that look to be approximately the same size as mine (I checked mine with some calipers and it has a 6-32 thread size). I did a little digging online and the phantom cup is apparently supposed to have a 6-32 thread as well. So it looks like that cup and cupseal might fit my gun. The only odd thing is that in their pdf manual they also show an eyelet (item #12 in the attached photo) that looks like it is used to hold the seal in place in the cup. However, even though they sell the cup and cupseal on their site, they don't sell that eyelet thing at all, so I don't know if it is really needed especially since my gun doesn't have that. I might just buy a seal and cup from them and see if that works. I saw a couple other sites that appear to sell the whole phantom cupseal assembly (including the eyelet already installed over the seal so I could buy that but since mine doesn't have that eyelet I'm slightly worried it might get in the way of my powertube retainer from sealing on the seal). I guess I'll find out. I happened to also see some cup/cupseals from Lapco and some others that appeared to be made from nylon or some white plastic. Are those made of some material where a separate seal isn't needed and the powertube retainer seals right on the nylon?

[DocsMachine]

I'm kind of surprised that CCI doesn't list a complete cup seal. Part #12 is sort of a "crush washer"- it keeps you from overtightening the cup to the power tube and squishing the seal out of the way. Your original cup has that kind of built in- that 'ridge' around the center hole.

You might try just getting the seal itself from CCI and seeing if it'll fit in your existing cup.

The solid plastic seals (usually something like Nylatron) do the same job and pretty well. It's generally regarded that the brass-and-urethane ones last longer, but I suspect that if you're not going through a couple cases a summer, it won't be an issue.

Doc.

[ekloot]

Yeah, I was surprised they didn't sell the complete cup seal assembly either. It looks like I'd have to buy the entire power tube assembly from them to get the complete cup seal assembly but I don't need the entire power tube assembly obviously. Plus from what I saw on another site, the phantom powertube is shorter than mine. I'll try just the seal first as you suggested since that is pretty cheap. If that doesn't fit then I might try buying one of those white plastic cup seals parts and try that. Thanks for your help! I'll post what ends up working for me in case someone else eventually comes along with the same gun and the same issue.

[Brokeass_baller]

If you have access to an o-ring kit, you might be able to stack o-rings in there and make it work.

But these were great guns. I owned two, and loved them both. One was standard open class, and the other was modified with a stock class feed block that took 10rd tubes directly. I wish I could find that one again. I'd buy it back in a heartbeat.

[ekloot]

Yeah, i originally bought this model because I was a poor college student over 20 years ago and needed a simple gun that was easy to maintain and I also didn't want to go through tons of paintballs. I had a lot of fun with this paintball gun back then. I still like how simple it is now and I look forward to have it back up and running. Hopefully I won't have to resort to trying orings but I'll keep that in mind if the phantom seal doesn't fit. I already placed an order for the seal this evening but with the holidays and all, I imagine it might take a little while to get.

[ekloot]

Okay, I finally have an update on this. I got the seals from PhantomOnline but they had to send me ones that were only for HPA tanks. Apparently they found out that the seals they recently got will eventually swell and cause problems when used with CO2 tanks so over the next month or two they are in the process of qualifying a different seal that will be suitable for CO2 tanks. They said these seals will work fine with HPA tanks though. Fortunately, they also said these HPA seals will work fine for a while with my CO2 tank before they swell so I can at least test them to see if they will work with my gun. If this all works, I plan to get an HPA tank anyways since my CO2 tank is 20 something years old (I'm surprised it still has CO2 in it and it still works after all that time). At first I thought the seals I received wouldn't fit my cup, but after cleaning all the goo out of the cup, I noticed that raised middle area is actually a separate eyelet much like the Phantom cup seal. So I took a pair of tweezers and popped the eyelet out of the cup and then cleaned everything even better with acetone and alcohol. Then I was just able to push the seal over the eyelet and then push it all back into the cup and screw the powertube back on. One thing I have to mention is that the seal is fortunately a little rubbery/flexible so it was able to stretch enough to fit over my eyelet (not sure if my eyelet is the exact same size of the Phantom eyelet or not). The guy at PhantomOnline did mention that when they eventually get the CO2 compatible versions of the seals that they will be a little harder so I don't for sure know if those will be able to flex enough to fit this eyelet. This HPA version of the seal did stretch enough obviously though. I attached some pictures of all this for anyone who might find it useful. I put the gun back together and it is not leaking air anymore and fires properly again. I have to wait to actually try shooting it with a paintball though because I'm in a condo in the suburbs and don't think the neighbors would appreciate me shooting this thing outside. Seems like it should work fine though. Thanks for the help and pointing me in the right direction. I really appreciate it!

[DocsMachine]

Glad to see it's working for you. I'd be curious to know what they're using that's not CO2 compatible.

Doc.

[ekloot]

I thought the guy said it was still a urethane seal if I remember right...it was a phone conversation and he was explaining it all fairly quickly. Mainly, I remember that he said that they originally thought these would work with CO2 but after they tested them for quite some time then they started to swell up but that they were fine for HPA. Also I remember him saying the next CO2 seals that they were soon getting would still be urethane of course but they would be harder and less flexible. They were the ones who actually reached out and called me to find out if I would be using CO2 or HPA because if I was using HPA then they could ship the seals that day, but if I was going to be using CO2 then they would need to wait 4 to 6 weeks while they got a newer batch of urethane for CO2 that wouldn't swell. When I explained that I was just trying to get the gun working with my existing CO2 tank but that I would be purchasing an HPA tank if I got the gun working properly, then he said he could ship the seals and would send a few extra for free since I might ruin a couple testing the gun out until I bought the HPA tank. They seemed really friendly and thorough over there. He did say to let him know how it worked out after I received them so maybe I'll send a message over and let him know and I can ask if this current seal is still urethane like I believe that he said.