Diablo Pump Bolt O-ring Question

[ekloot]

Hi everyone, I've got another question about my CMI Diablo Pump (Nelson style pump). I'm trying to find a replacement for the original Bolt oring. I measured the original with some calipers and ordered a few close sizes but am wondering how tight the bolt and oring is supposed to be fitting into the body/barrel part that it goes into. With the gun unassembled and just dropping the bolt into the body it'll slide to the farthest forward position all on it's own by just tipping the body downward. This is with the bolt and oring completely dry with no lube or anything. I'm assuming it isn't supposed to be this loose and the oring is just worn out? I'm guessing with it this loose it wouldn't be making a full seal. So my question is if the bolt oring is supposed to be making an actual true seal all the way around, or is that oring just there to keep the metal parts from rubbing into each other? One of the new orings seems to let the bolt slide just as loosely as the original...so probably not completely sealing but don't know if that's okay. One of the other new sizes seems almost too tight and I have to push the bolt into it's place. I haven't tried it with the oring lube yet though, so maybe it is supposed to be that tight and will loosen up with lube and with some time to break it in? Not sure how loose the bolt should actually be moving back and forth.

[Jonnydread]

Is there a return spring on the gun? If so it makes sense that it would fairly easily slide into the forward position. You may need to find a thicker durometer o-ring to get an appropriate seal. The seal shouldn't be so tight that it impedes movement of the internals, but tight enough that you don't get any blowback air up the feed. It should fit into place with just a tiny bit of force required. If you post some pictures we could provide more specific advice. In short, yes the bolt o-ring should be creating a seal.

[ekloot]

No, there is not a return spring on this model. Based on what you're saying, I think I probably need to use the oring that makes the bolt fit a little tighter rather than sliding around loosely. I can take some pictures when I get home later though. I don't know if this will let me upload a video but that would probably show it best.

[Jonnydread]

Yeah it sounds like you need a fatter o-ring. If you post to YouTube you could link it, that may be easier. I'll see if I have any spare Line SI bolt o-rings, if I do I'd be happy to send you one.

[ekloot]

Okay, here's a video I recorded of what I was seeing. The first half of the video is with the original bolt oring. The second half of the video shows how the bolt is tighter with one of the newer orings that I got. That particular newer oring seems to be the closest fit to the original while actually maybe making a seal but it almost feels like it might make things too tight but I'm not sure. https://youtu.be/101ljLIxdIE

[Jonnydread]

Okay from the video I’m thinking the second one, but it kind of seems like a Goldilocks situation cause the bolt should move freely but create enough of seal that you can’t really feel sir blowing up the feed. I would try shooting it with the second o-ring and seeing how it feels. With the pump attached I doubt the extra effort will be something you even notice.

[ekloot]

Yeah, I'm thinking you're probably right. I'll give it a try. Definitely appreciate the help. Also, I might create a separate thread to ask this, but my powertube assembly seems to have an odd oring that appears to be flat on the back side and somewhat rounded on the front. I can't seem to find anything like it online. Is there a name for this type of oring or somewhere I can find these? I attached a couple pictures showing it in its correct position as well as pulled up so it can be seen better.

[Brokeass_baller]

It's a standard o-ring, just deformed from use and squeeze. I owned two Diablos in the past and fixed them with standard Bunas.

[ekloot]

Okay, thanks. That makes sense. It looks like one of the orings I already got (size 112) to try with the bolt will also be a good fit for the powertube retainer.

[Chappy]

What oring did you end up going with? How did it work out?

[ekloot]

For the bolt, I went with a 11.91mm ID x 2.62 CS buna 70 oring that I got from theoringstore.com but I think I could have also used a regular size 112 buna 70 oring. The first one seemed to be a tiny bit better fit though. For the powertube assembly, I just used the size 112 buna 70 oring since it seemed to be a perfect fit in there. That one I had originally got at phantomonline.com (it is the bolt oring for phantom pump guns)...but I'm sure I could have used any size 112 buna 70 oring. The gun shoots well now. Only have had time to shoot it out in the yard but I got one of those handheld chronographs and after adjusting the gun's velocity adjustment, it's shooting around 270fps. I did also end up replacing the valve spring and the main spring with green ones that I got from baccipaintball.com. Those green springs are both listed on his site for the Kenimex gun but they are a perfect fit in mine as well. Before I changed those springs, the gun's velocity was a little more erratic. Maybe my original springs were more worn out.