Ben Savage

This morning I had a delivery of the parts which I thought would get everything fixed, and thankfully the piston now fits much better. I also had a look at the new piston width info in the descriptions, and I was unlucky enough to have bought the widest piston that there was, so I likely could have tried a different XT piston. The selector plate on the other hand doesn't seem to be a straight swap - I have lost semi auto, it seems like the dimensions are very slightly different between the rocket selector plate and the original, so I am wondering if I should try to remove material to make the circled parts (image below) the same size as I am guessing that is the main issue. After reassembling, it still didn't sound as good as I had been hoping - and I realised that it will now be the shimming. The issue I have been having with the shimming, is since getting the new screws which are holding the gearbox shut tighter, the spur and sector gears are too tight from a single 0.1mm shim, so I decided to not use any shims for these gears. I'm now noticing that the spur gear is clipping the bushing for the sector gear, and possibly even the bevel gear as well. This is an issue as if I put 1 shim below the spur gear to lift it above the bushing, it then becomes difficult to spin. Do I need to buy low profile bushings to solve the bushing issue? Or is there an alternative solution which would be better (maybe tapering the edges of the gears)? And the most recent thing to have gone wrong for this build, is the positive wire on the battery side of the trigger contacts, is hanging on by a thread. It wasn't soldered very well from factory, so I'm now trying to decide whether to get the soldering iron out if I can find it, or go ahead and buy a Perun hybrid. I'm leaning towards soldering it back on, as I don't think I should try fitting an etu + mosfet until everything is working. Thanks for all the help so far, hopefully I don't encounter any more issues after resolving the above.

I paid around £100 in December, with the intention to gut it and get a bit more practice at working on AEGs, some parts are shockingly poor, such as the gearbox screws and the body pin which holds the gearbox in which were both seemingly made of cheese from how easily the body pin deformed and how one of the screw heads snapped off before the screw was tight. It was a bit alarming that it arrived firing 450fps (especially from a UK shop) and I think that some of the cheap parts used were probably not suitable for such a strong spring and would not have lasted very long. I have a couple of Cyma 002 M4 CQBRs which have the metal receivers, and I expected the cylinders/inner barrels to be the same, but the cheaper CM603 has what appears to be a red anodised cylinder and inner barrel, whereas the more expensive CM002 has what appears to be brass cylinders and outer barrels. I found the finish on the cheap inner barrel and cylinder to be better than I had expected, but I still plan on replacing the barrel with either an XT (If 380mm is available) or ZCI (although I've seen their quality is declining), and the cylinder I had used originally until the piston head screw scratched the inside after coming free. I'm thinking of ordering some ZCI 14 teeth pistons for the current build (as the previous one worked quite well before my mistake) and having a few ready for when I decide to work on the CM002s which I plan on doing the same work to, as they already have a tooth removed which will probably be better than me attempting to remove a tooth from a Cyma piston as I don't think I would be able to do a neat enough job to be happy with.

The stock piston had one metal tooth, and the rest were plastic so I thought it would be best to go for a full metal rack piston.

Ah thank you, that seems to be the issue - I did as you said and it required quite a lot of force to move the piston within the gearbox, I then tried the stock piston which moved very easily, and then the remains of the previous piston could move but not quite as easily as the stock piston. I hadn't realised that the width of the piston itself could be an issue. I will see if I can do anything to make it move easily, otherwise I will buy a different piston and hope that it fits.

Thanks for the reply, with regards to the motor, I was considering short-stroking the sector gear by a few teeth, especially as I have bought a ported cylinder, so the last few teeth of the sector gear are not causing any extra volume in the cylinder. Would short-stroking reduce the need to go for a higher TPA motor as the spring won't be being compressed as much? Also, I gave everything an inspection after the piston head detached, and anything which had even a slight bit of damage was replaced, so it doesn't seem to be any remaining damage that is causing an issue. With the piston potentially being the issue, I am thinking of trying to swap the rack on the new piston with the old one, as the previous rack didn't get damaged but I am unsure about if it is a bad idea to swap the racks on pistons by different manufacturers. Although when turning the gears manually with the piston in place it doesn't seem to be catching on any teeth so I don't know if that means it would be unlikely to be the problem.

Hi all, I'm having some issues upgrading a Cyma M4, with the sound coming from the gearbox being quite poor. I'll give quite an in depth description of how the issue started, as it wasn't doing this from the start. I bought a Cyma CM603 for a low price in December with the intention to learn to upgrade and tinker with AEGs. It arrived firing 450fps on a 0.2g bb, so I needed to make some changes to it before I would be able to take it to a game. I initially bought the following parts: SHS High Torque Motor SHS 13:1 Gears ZCI 14 Tooth Piston XT 6 Vent POM Piston Head XT Steel Spring Guide XT M100 Spring I had to grind away part of the gearbox shell to fit the gears, as the Cyma gearbox is reinforced which prevented the spur gear from fitting properly. After doing this, I did my best attempt to shim the new gears. I attached the piston head to the piston, but forgot to use any thread lock when doing this. I then didn't have any time to continue for a couple of months, so I resumed the build this week. I found that everything looked good and ready to assemble, so I put everything back together, and it sounded like it was working great. I was achieving 20rps on a 9.6v NiMH, and it sounded quite good. I then was doing some more test firing, and suddenly a horrendous sound started happening so I stopped firing and disassembled the gun to find the screw holding the piston head had come out (Presumably due to forgetting to use any thread lock), causing a lot of damage. The piston, piston head, cylinder and spring were all damaged, so I purchased replacements. I was unable to get the same piston which I had previously used, so I bought the following replacement parts: XT 14 Tooth Piston Swiss Cheese XT 6 Vent POM Piston Head XT Metal Cylinder Head (Original plastic one wasn't damaged, but gave a poor air seal) XT M100 Spring ZCI V2 Gearbox Screws (I had a screw head snap off the original ones during assembly, so I assumed they were all low quality so replaced them all) After these parts arrived, I then reassembled the RIF and was hoping to have the same success as I had previously, but it sounded horrendous. I tried adjusting the motor height and it only sounded marginally better, so I assumed it would be the new gearbox screws making the gearbox close tighter, meaning I had to reshim. I then disassembled it and closed the gearbox back up with just the gears in, tightened the screws as they were before and tried to spin them, and they were quite tight with the new screws being used, so I decided to start reshimming (It is worth mentioning that the gears, motor pinion and piston teeth all had no signs of damage/wear). I then tried to shim it again from scratch, and after I was happy with it, I reassembled everything and test fired the gun. After reassembling it, I started test firing it and it sounded better than it did before, but it still sounded quite poor and very far away from how it did sound. I tried adjusting the motor height in both directions and I didn't really get any improvements, so I'm wondering what people think on here. I think maybe my shimming could have been done poorly this time, but before completely starting again I thought I would ask for opinions. I've attached a couple of videos of how it sounded before the piston head came off, and after my repairs. Please let me know any thoughts on what the issue could be. Any help would be appreciated, thanks. Before breaking After Breaking

Thanks that has done the trick, relieved it was such an easy fix.

Hello all, more gun problems unfortunately.... A couple of weeks ago a group of us went to a game, and in the lead up my mate's M249 had been functioning perfectly, but when we got to the game, we put the battery in (9.6V 1600mAh NiMH), and the gun would not fire. We tested with all of our batteries, before ruling these out as the problem. When the trigger is pulled, there is no sound from the gun except for the 'click' sound which is made when the trigger is pulled. The wires get warm extremely quickly, and no electrical sound is made from any part of the gun. We had an idea it could be the fuse, so after ordering a box of fuses, I then realised that I foolishly bought fuses which are too small to fit , but we managed to test these fuses still, and it did not change anything unfortunately. If anybody has any idea what can be done to fix this, it would be great, thanks.