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Line SI Promaster

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    Line SI Promaster

    Click image for larger version  Name:	image_2730.jpg Views:	3 Size:	1.03 MB ID:	16676 Do any of you have personal experience with Line SI Promasters? Do they require anything special regarding a service/rebuild? I have not torn mine down, but it's supposed to be complete.

    EDIT: Rear Upper Bumper and Screw are missing.

    I found the Pukin Dogs Promaster page, but have not digested it yet.

    These guns look to be fairly tunable, but may require unobtanium parts to sweet spot.

    Last edited by un2xs; 08-10-2020, 05:45 PM.

    No, but you inspired me to try tearing mine down again. It doesn't want to function, and I think it mostly needed a deep cleaning as well as a light deburring of the torn up bolt.

    I discovered my detent spring is rusted through from years of sitting in paint gunk. Gonna try to fashion a replacement from a pen spring
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      So on further inspection, I figured out the bolt is getting torn up (and sticks) due to the RAGGEDY EDGE OF THE FEEDNECK STICKING DOWN INTO THE BORE. I'm honestly shocked at the workmanship. Mostly the gun seems exceedingly well built

      While l figure that out, I also need a rebuild
      Last edited by Axel; 08-03-2020, 06:57 PM.
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        Well, 20 minutes or so with a set of files and I've fixed my bolt stick issue. I should have gotten a picture first. It looked like the feedneck was rotated slightly on its central axis so that the two wings were sticking down into the bore instead of lining up with the tube of the barrel snub. And beyond that, the finish of the machines edges on the elbow look horribly chattered. I'm totally perplexed how this happened, because the gun was completely unfirable, but the condition and especially the breach wear indicates that this gun has seen some action. Would the feedneck unthread from its mount?

        Anyway, the gun leaks like a sieve but I did get enough air pressure to confirm that blowback is functioning properly. Next step: rebuild with fresh seals.

        Un2xs, what are these unobtainium parts you need?
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          Originally posted by Axel View Post

          Anyway, the gun leaks like a sieve but I did get enough air pressure to confirm that blowback is functioning properly. Next step: rebuild with fresh seals.

          Un2xs, what are these unobtainium parts you need?
          Axel, you have given me hope for this fine old specimen... No, not me... my Line SI Promaster.

          To be honest, I do not KNOW that i will need some of those parts. The PukinDog page mentioned some parts that let him fine tune his Promaster. Promasters were his goto for a while.
          Even when I owned an AGD Minimag, the Promaster was still my first back-up and often used. In warm weather, I preferred the Promaster over the Minimag because of it’s ability to be incredibly accurate without being paint picky.
          I suggest this last bit might be due, in part, to the lever style detent which continued to be used on all of the Cats.

          Mine had some rust on the detent when I bought it... I did a bit of cleanup at the time. Externally it does appear to be mostly intact. I have not taken it apart yet or aired it up, so I do not know if there are any surprises to be found. (When I bought one of the Alaska Nelson's I was also gifted with a couple of vintage paintballs in the barrel. Doc is a generous guy like that.)

          Here is the paragraph from PukinDogs that had me reference unobtanium:
          Eventually, I discovered that valve chamber extensions made for Spyders would fit the Promaster (imagine that!), although some models require some large amounts of pipe tape to seal properly. A large Shocktech volume chamber combined with the Taso high-flow valve/valve pin also made for a Spyder (which simply drops right in) offered a great improvement in the ability to move a larger volume of gas through the system.
          It could be that all of this stuff can be matched with current off the shelf parts, but I do not know enough to know.

          Its good to see your progress. If I am lucky, I MIGHT get away with just re-ringing mine.

          un2xs in Kansas


            Do you know the o-ring sizes? I assume that the valve orings and stem/cupseal assembly are Spyder compatible but haven't checked.

            The only one listed in the manual and schematic at ICD is the 006 Buna air passage sealing ring between the ASA and body
            Last edited by Axel; 07-28-2020, 08:25 PM.
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              O-ring investigation, based on a print out sizing chart from Captain O-ring.

              Keep in mind, I have no idea how old these rings are and they may have swollen or stretched. I put an asterisk next to the better fit where it appeared to be between two sizes.

              The little ASA air passage ring is confirmed size 006 Buna according to the manual. The bolt o-ring might be the same material.

              I'm not sure if the coloration between the other four indicates a different material, or possibly more exposure to oil or CO2 on the bolt and the back of the valve.

              My plan is to buy a handful of o-rings in sizes 015 - 017, in different materials if I can get them, and see what works.

              The cupseal unscrews and is rebuildable. I flipped mine over. It's a hard material, perhaps Teflon

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                Success! I just did a rebuild of the above rings and resolved all of my leaks.

                The good news is that I was mistaken on most of the o-ring measurements, and in fact the majority of these rings are 015. It was painfully obvious when I tried fitting 016s that they were simply too big. I had both buna and polyurethane, and used the harder poly where the originals seemed stiffer, on the rear valve and valve retention screw. The front valve and hammer got buna. This means your primary o-ring to rebuild this guy is the standard tank o-ring

                For the bolt o-ring I did end up using 016 polyurethane. The groove is a bit deeper and it's harder to tell how well it sits, but it looked OK with a 016 and it's working fine.

                I thought I had a leaky cup seal last time, and I've ordered a Piranha valve stem to test it out as a potential replacement, but it turns out it was probably the valve o-ring letting air into the barrel.

                There are additional seals inside the ASA, but as that assembly is held in place with two spring pins, I'm not attempting to take it apart unless it starts leaking.

                So the last step for me is to just get this baby over a chronograph and dial in the FPS.
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                  As stated before, the cup seal is rebuildable, so it should not prove difficult to replace even if we had to punch our own from sheet material. But that's not going to be necessary.

                  Option 1: I picked up a Piranha valve stem from our fellow member sugarstump (, and no surprise, it drops right in. The stem is a bit longer, and I'm not sure if that affect the hammer impact to any measurable degree, but the cup is also longer, so it will increase valve spring tension. I get 11 or 12 shots off a 12 gram, and without changing anything else, the Piranha valve stem yielded 23 and 17 (I probably shot a bit faster the second time). Spyders and clones (which are ultimately Promaster clones) are going to give us lots of options. It's probably worthwhile to acquire a variety for tuning purposes.

                  I should say here that the pukin dogs article in post #1 says the Promaster "had valve pins with different amounts of flat sides for controlling re-cock pressure." Mine has a single flat; the Piranha stem has two. It would be interesting to know what options came with the original.

                  Option 2: a BT-4 cup seal should fit the Promaster valve stem assembly with a little cajoling. The OD is about right; the ID needs opened. I did not bother to try fitting it, but it's worth mentioning.
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                    Promaster SI on the left, Piranha on the right
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                      I was going to ask you about valve stems, but you beat me to the punch. The owners manual mentioned two different valve stems... a #1 and a #2. However, the schematic lists #2 and #4. Do you have any idea why the difference or what they mean? Or do we have to go to the source in Idaho for this one?


                        Just what the pukin dogs article said. I have no idea which one I have or how many varieties exist
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                          I just dug my Promaster out of the stack. For some reason I never noticed that mine is missing part #5 Upper or Rear Bumper. Is this really a bumper or is it just a cap to close the upper tube? If bumper, what material is it? (I did not see a spring on the schematic.) Is the "bumper" even required for proper functionality?

                          Just wondering... is that a two piece bumper made of a rubbery material in a metal cap like the later Cats used?

                          Click image for larger version  Name:	20200808_214029.jpg Views:	0 Size:	1.11 MB ID:	16570

                          At this point I am leery of taking it apart for fear of what I will find. (Or not find?)

                          The gun currently cocks and dry fires. Have not dug out the 12g and lever changer yet. I am betting a complete re-ring is in order.

                          Axel, if it matters, my main spring appears to be red in color.

                          Is the screw on the bottom of the ASA the only thing holding the hammer & bolt in the besides the cocking knob?
                          Last edited by un2xs; 08-08-2020, 11:29 PM.


                            I think I read somewhere that the back cap is not really necessary. It's a round rubber bumper somehow attached to an aluminum cap, held in place with a thumb screw. There's also a bumper behind the hammer which is probably more important

                            I don't know about the red spring. Maybe it's from a tuning kit like the Madman Spyder spring set. Mine's just plain uncolored metal

                            The ASA is held on by just that one screw.

                            PM me your address and I'll mail you a set of rings. I uh, .... I have plenty.

                            Attached Files
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                              I don't think you'd have anything to worry about taking it apart, but I'd advise you not to open the grip frame. There's one cap screw in front of the trigger guard, and then you have to remove the trigger shoe, and the frame hinges open on a pin in the back. You can see the pin if you look at the back of the grip right above where the webbing between you thumb and forefinger sits, and you can probably see the sear spring hooked around the pin. Getting that spring back on the pin and then lining everything up correctly to reassemble is a mild PITA. There's no seals in there so unless you want to mess with the trigger/sear assembly or the safety, there's no reason to go in there.
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