Cyma spring replacement

[Sam0001]

CYMA CM.513 M4 RIS Suppressed how easy is it to change the spring 

Looking to use in cqb with FPS 300 

 

If relatively easy where would I find instruction ?

[Rogerborg]

It's a standard V2 gearbox, so any generic instructional will do. These are as good as any, to get the gearbox out, then apart.

 

 

 

 

I found that the gearbox on my CYMA took a good hard tug to get it out of the shell - you just need a bit of self confidence at that point.

 

You only need to get it far enough apart to change the spring, although once you're in there you might as well check the shimming and sort the lubrication as well.

 

The only fraught bit is getting it apart while it's still under spring tension: note that you need to push down on the spring and cylinder while you're splitting the gearbox, and get a screwdriver or similar into the spring guide to hold it down.  It can be risky the first couple of times, and you might want to do it inside a clear plastic bag in case it all goes wrong and yeets the internals into hyperspace.

 

Re-assembly is the opposite, and it does help to have 3 hands, or put some neodymium magnets under the box to hold the gears and latch in place and/or use an anti-reversal latch tool to hold that piece in place (eBay or ak2m4 although I can't find it there at the moment).  You might benefit from taking a few picture as you go for things like which way round the latch goes, although there are loads of videos out there.

 

As to what spring you'll need, notionally an M90 should be about right, but it all comes down to the air seal, and cylinder to barrel volume.  A chrono is invaluable for taking the guesswork out of it.

[RostokMcSpoons]

1 hour ago, Rogerborg said:

The only fraught bit is getting it apart while it's still under spring tension: note that you need to push down on the spring and piston while you're splitting the gearbox.  It can be risky the first couple of times, and you might want to do it inside a clear plastic bag in case it all goes wrong and yeets the internals into hyperspace.

 

Re-assembly is the opposite, and it does help to have 3 hands, or put some neodymium magnets under the box to hold the gears and latch in place and/or use an anti-reversal latch tool to hold that piece in place (eBay or ak2m4 although I can't find it there at the moment).  You might benefit from taking a few picture as you go for things like which way round the latch goes, although there are loads of videos out there.

 

 

 

+1 for all that.  The first time I split the gearbox the spring flew out sideways and the trigger and all the gears were everywhere, and I didn't have the self-confidence to try to put it back together.
But if you spend enough time looking at the internals, they're not actually that complicated and most of the stuff fits together quite logically (although it may be oh so super-fiddly).

The one real terrifying thing is if the spring goes flying and knocks the shims off your gears.  Learning to assemble / disassemble the gearbox AND learning to shim at the same time is a bit of a steep learning curve, so do your absolute best to ensure that spring is held in place.  And then look carefully on the gearbox shell for any shims that may be stuck there, so you can keep track of where they ought to be.

The anti-reversal latch is a complete PITA so another thumbs-up for using magnets to keep it in place during reassembly.  I actually made a jig of a small piece of wood with some nails and screws in it to act as a third pair of hands when putting my gearbox back together.   And then I stacked some magnets into a hole in the wood under the latch to hold it.  But you can just stick them straight on the shell.

It ain't pretty but it works...

(this is a v3 gearbox btw)

 

Edited January 31, 2022 by RostokMcSpoons

[Rogerborg]

2 hours ago, RostokMcSpoons said:

I actually made a jig of a small piece of wood with some nails and screws in it to act as a third pair of hands when putting my gearbox back together

 

What a great idea, especially for V3 gearboxes and those fiddly two-part triggers.  The MP5K trigger in particular is a absolute mare to get in place while re-assembling - I gave up and actually twisted a bit of tension out of the spring.

[Druid799]

8 hours ago, RostokMcSpoons said:

I actually made a jig of a small piece of wood with some nails and screws in it to act as a third pair of hands when putting my gearbox back together.  

Similar sort of tac , many moons ago I made a similar sort of jig’a’mathingy to work on V2 gearboxes . My one was a piece of board approx 6inch X 10inch with a piece Approx 4inch X 6inch screwed upright at one end , hole drilled through then a nut epoxied into the hole so a threaded rod could be screwed through that in tho the spring guide to keep it ‘tied down’ , an oversized outline of a gearbox around it with lots of holes that corresponded with the body screws from the gearbox to keep them safe . Unfortunately don’t have it anymore to take any pictures of it as even with this magnificent example of a homemade jig to assist me when I wanted to work on my guns my self  ,,,,,,,,,,,,,I STILL SUCK AT TECH WORK !!!!!!!🤦‍♂️
So I gave it to my mate who fixes any busted guns for me ! 😁