Disassembly instructions for IZM Baikal 46M to change the piston seal



Author Topic: Disassembly instructions for IZM Baikal 46M to change the piston seal  (Read 236 times))

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In order to enable rated velocity, I wanted to adjust (reduce) the residual compression volume on my 46M. 

In looking for guidance on how to take apart the piston and cocking linkage assembly , I found instructions for how to change the piston seal. 

I wanted to attach them in their original "slide show" file format, but GTA won't accept such large files; nor .exe files.  So, copied, compressed and attached the images below...


I took my pistol apart and put it back together, so now feel armed to provide further advice on the topic :)

Do yourself a favor; take the front sight off.  Leaving it in place forces contortions of the piston to get it in and out.  I was not prepared to risk any damage to the seal, so I took the front sight off.  Not that the end of the compression cylinder is sharp, but as a matter of general principle; why make something difficult when it does not have to be.

At first, I could not get the left hinge support guide, shown in "photo 8" to come out of the compression cylinder.  I was not going to brute force it.  Then it occurred to me that the "barrel band" had slightly collapsed the compression cylinder, such that the hinge support guide was being trapped (due to the fact that the cylinder has a groove cut at the front).  Removing the barrel band freed up the "stuck" part.  However, I would advise against completely removing the barrel band, unless you have no other choice: 

The most difficult aspect in taking apart and reassembly of this pistol was reinstalling the barrel band.  I battled to get the screw to start in its nut.  Later figured out the nut was canting over in its recess.  Thus, my suggestion to not completely unscrew the barrel band retaining screw; if you can help it.  I believe that just taking the load off the compression cylinder by breaking the tension on the barrel band screw should be enough...

To remove the valve actuating plate on top of the barrel, cock the valve by flipping up the TP lever by hand; without charging the pistol with air.  The rear of the piston needs to be forward of the the little window in the top of the cylinder that the valve cocking plate hooks into.  The rest of this action is explained in the attachment, and it is as simple as it looks.

Once you have the pistol stripped this far, it becomes apparent that it really is beautifully simple in design and construction; and quite easy to work on.


Had to attach individual images due to single file size limitations.  Continued below...
« Last Edit: January 13, 2019, 12:50:39 AM by subscriber »
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Re: Disassembly of IZM Baikal 46M to change the piston seal
« Reply #1 on: January 13, 2019, 12:39:57 AM »
Continued from above...
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Offline Stinger177

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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #2 on: January 13, 2019, 11:32:03 AM »
Peter - Thanks for going to all that work to post those pics. I have never seen the internals of my 46M.

I also saw your thread about adjusting the piston stroke - https://www.gatewaytoairguns.org/GTA/index.php?topic=153027.new;topicseen#new

Something else I didn't know about.

I'm thinking that the latest 46M's came with better instructions than when I bought mine 14 yrs. ago. Mine didn't even come with extra seals.
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Offline Manning

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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #3 on: January 13, 2019, 12:56:17 PM »
Thank you!
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Offline theanalogman

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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #4 on: January 13, 2019, 05:48:42 PM »
Thanks! I wonder if I will ever get this advanced....
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Offline Stinger177

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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #5 on: January 13, 2019, 06:15:29 PM »
Thanks! I wonder if I will ever get this advanced....

I'm packaging and labeling your seals this very moment. Will get them off to you tomorrow morning.
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Offline Yogi

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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #6 on: January 14, 2019, 02:28:21 AM »
In order to enable rated velocity, I wanted to adjust (reduce) the residual compression volume on my 46M.

You lost me. ???  Do you mean to say that you wish to reduce the length of the piston stroke? :-\  Does the shape of the face of the piston seal make that big a difference?

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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #7 on: January 14, 2019, 03:06:32 AM »
Yogi,

Short answer to the first question, is "no".   Reducing the stroke would increase the residual volume.  I reduced the residual volume, without changing the stroke length.


The long answer is this:

There is the swept volume and the residual volume.  I wanted to decrease the residual volume.  Changing the swept volume can't be done without using different link lengths, and/or moving the vent hole in the (top of my) cylinder.

The swept volume depends on the bore and piston stroke.  I did not change that.

The compression (and expansion) ratio depends on the swept volume / residual volume.  To increase the working pressure (and thus the power), I decreased the residual volume:

The residual volume (at the end of the full stoke) depends on the volume of the valve, plus the space between the end of the piston and the "cylinder head".  I decreased the residual volume, by screwing the piston a 0.5 mm half a turn closer to the cylinder head; away from the connecting rod pivot pin; by relative motion at the thread visible in the piston's backside ID.

Any other questions :)
« Last Edit: January 14, 2019, 03:16:13 AM by subscriber »
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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #8 on: January 14, 2019, 03:12:49 AM »
The shape of the piston face matters.  It has a deep wide groove in it, as part of the "parachute seal" design.  The groove is part of the residual volume. 

Air trapped in the groove would be slow to flow out, and thus makes the system less efficient.  Filling the groove with thick grease that stays in place would reduce the gap, while still allowing the seal to function normally.  This would boost performance noticeably, based on my recent exploits.  However, if you filled in that groove completely with grease (you could partially fill it), you might need to back off the piston adjustment (opposite of what I did), or the cocking force may be so high that the linkages can't handle it...
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Re: Disassembly instructions for IZM Baikal 46M to change the piston seal
« Reply #9 on: January 15, 2019, 01:13:37 AM »
If you came here to try and understand this pistol's mechanism, you might find this thread helpful:  https://www.gatewaytoairguns.org/GTA/index.php?topic=153475.msg155688851#msg155688851
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