M4 Long Gearbox Upgrade

Hello everyone!

The Cyma M4 Long is my first Gel blaster and I’m looking at diving in head first and swapping out the nylon internals for metal ones.

From what I can gather, the Cyma blasters use a V2 style gearbox (Not that I know what the difference between the versions are), and most parts should be easily swapped with the exception of the piston and piston head as they are borderline proprietary parts.

I’m not looking for super high RPM, I want to gain a generally reliable hard hitting blaster.

Here’s the part-list I’ve put together;

I feel like I’ve covered all the bases, but is there anything I’m missing? Anything you would do differently to achieve the same goal?

Any advice you can give me would be greatly appreciated!!


I would scrap that 15T and stick with the 14T, get a good piston head and plunger with steel teeth. Don’t get that compressed metal crap. If your inner barrel is long, 28cm plus start looking for a 100% cylinder and maybe you will need to port it to 90%. 18-1 is a good ratio but if you fit that it would be a toss up as to bearings or bushes. Just my take on it. Change all the O-rings, even if they are new for good green ones and a little silicon oil helps when fitting and during operation. Because CYMA has a mongrel propriety spring retainer with four locking pins, you will not find a suitable replacement easily, add to that the fact that the buffer tube screws into it as well. J9 Spring metal retainers with the bearing on them are best fitting and allow the spring to spin as it compresses instead of eating up your plastic/ nylon/polymer original retainer. FYI, the original motor should have been a 480 anyhow and if true to form the barrel will be an inside diameter of 7mm. They are a loosely based Gen 2, but a mongrel as well.

I have just finished mine, it runs a 350mmx7mm barrel and I use the full 100% still using the all nylon gearbox.

Your spring sounds like it is too heavy for the housing, The original should be a 1.2mm equal at 15cm +/- 1cm.

My first move was to an M100 SHS 1.3mm-15.5cm unequal spring and whilst it worked, it was unforgiving on the whole blaster. I have now fitted an M90 1.25mm-14cm unequal spring. It still hits the same distance but more control and less hammer.

Good luck, watch some videos on stripping and assembly before you dive in, enjoy it. Oh, have some lubrication for it too, you can buy it from these places as well and the greases are labelled.

Welcome to the Forums.

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Thanks for the reply!

Are the bearings/bushes pushed into the center of the gears or in between the gearbox and the gears themselves?

Are there many other blasters that have parts that work in the Cyma? I see “Well” have parts that come up when searching for Cyma parts, I also see alot of Gen 9 and Gen 8 parts, is this because the parts will work? Or because they are all M4 style blasters?

I have updated the parts list to include a 100%, 14 Tooth piston and M90 Spring. Let me know what you think!


Happy to help. First off this video is great.

I have been told Kublai parts will fit, but I did the same as you. If you want to cut your costs then get your CYMA parts Piston head and Nozzle and a few others to make postage worthwhile from Monkee Mods. Right now less than half price of what you are listing, even the 18-1 SHS gears. Just don’t wander off into the Nerf ■■■■ LoL
The bushes should just press out from the outside in, and then getting 8mm replacement bearings, you press them back in from the inside. Just be careful how much stress you apply to the housing.