TM mp5 reassembled, making noise but not firing

[The Madcap]

Hey. I got a TM MP5 about a month or so ago. After reading on here that it was shooting too hard I decided to buy a PDI 170 Spring to replace the Systema M130 spring that was in it when I bought it. I have had to disassemble & reassemble it many times for various reasons (shimmed too tight, trigger not springing back, forgot parts, etc.). So anyhow, I tore it appart again today, reshimmed it, lubed everything & put it back together (I was sure that I got it right this time!). When I went to fire it seems as if everything is working right, it sounds right, I can hear the cylinder moving when I pull the trigger but the damn thing will not fire .20 gram bbs! I have some cheap .12 rounds that it will fire sporadically but it just isn't working right. Since I want this to be the very last time I have to do this for awhile can somebody give me a heads up as to what exactly I should check before reassembly? I am guessing that it has something to do with the cylinder compression but I don't know what I did wrong. So what do you guys think?

[Mantelope]

You've probably disconnected the nozzle from the tappet plate.

[Wolfman]

Originally Posted by harleyb

You've probably disconnected the nozzle from the tappet plate.

Yep.... what he said! ^^^

[CDN_Stalker]

For starters get rid of the PDI 170% spring. PDI spring quality has gone to shit the past while, mainly in their 150% range, but I've heard of 170% shooting as high as 450fps recently. Tear it open again, put your finger onthe nozzle to see if good air comes out each time.

Harley, he says it'll fire 0.12g sporadically, so it means at least the tappet plate is pulling the nozzle back to load a BB and shoot it out. Sporadic doesn't sound like no nozzle movement, should be all the time or none.

Just out of curiousity, shoot the gun w/o mag on full auto til you get the nozzle sitting full back in the mechbox. Then make sure the gun is unloaded without a battery in it, take a flashlight and shine it up into the loading tube while looking down the end of the barrel. See if you can see the light, if so, reduce the hop up to off and increase to full the hop up to see if it moves freely. Sounds like you might be getting some barrel plugging (like maybe your hop up rubber tore and is plugging the barrel........ happened to me once, is why I say). If hop up is fine, you can not see a nub at off and can see a nub at full, put a drop or two of silicon oil into the loading tube (gun upside down) and run a few mags through it. Could be your hop up rubber dried out and got sticky, preventing BBs from loading and firing. I just got my previously perfectly working MP5 back from a team mate that painted it for me, it was plugging most of the time too, even on no hop up. I swabbed the barrel with oil, put a few drops in the loading nozzle, ran a couple mags through it, perfect. Hop up on, perfect. Overspray got in the breech in my case, but could be yours never got an oil job and the hop up is jamming BBs cuz it needs oil.

[Mantelope]

It could very well be that the nozzle is in a rearwards position, or removed entirely, and only .12g BBs are light enough to be pushed into the hopup by the much weaker air force.

[The Madcap]

Originally Posted by CDN_Stalker

For starters get rid of the PDI 170% spring. PDI spring quality has gone to shit the past while, mainly in their 150% range, but I've heard of 170% shooting as high as 450fps recently. Tear it open again, put your finger onthe nozzle to see if good air comes out each time.

Harley, he says it'll fire 0.12g sporadically, so it means at least the tappet plate is pulling the nozzle back to load a BB and shoot it out. Sporadic doesn't sound like no nozzle movement, should be all the time or none.

Just out of curiousity, shoot the gun w/o mag on full auto til you get the nozzle sitting full back in the mechbox. Then make sure the gun is unloaded without a battery in it, take a flashlight and shine it up into the loading tube while looking down the end of the barrel. See if you can see the light, if so, reduce the hop up to off and increase to full the hop up to see if it moves freely. Sounds like you might be getting some barrel plugging (like maybe your hop up rubber tore and is plugging the barrel........ happened to me once, is why I say). If hop up is fine, you can not see a nub at off and can see a nub at full, put a drop or two of silicon oil into the loading tube (gun upside down) and run a few mags through it. Could be your hop up rubber dried out and got sticky, preventing BBs from loading and firing. I just got my previously perfectly working MP5 back from a team mate that painted it for me, it was plugging most of the time too, even on no hop up. I swabbed the barrel with oil, put a few drops in the loading nozzle, ran a couple mags through it, perfect. Hop up on, perfect. Overspray got in the breech in my case, but could be yours never got an oil job and the hop up is jamming BBs cuz it needs oil.

Thanks. Now how do I know that the nozzle is sitting all the way in the back of the mech box? I dry fired a bunch of rounds so I am guessing that it is? Put some light up there. With the hop up on(?) light was passing thru, off-no light. I am going to pick up some silicone tomorrow but it seems awfully strange that it would go from shooting perfect to not firing a single .20 bb. So frustrated. Good experience I am sure but frustrating none the less. :smack:

[CDN_Stalker]

You have NO idea what the word frustration means when it comes to AEGs! Lol, I've seen things that I never would have expected, like an aftermarket piston having too tight of a groove on the sides causing it to jam up in the mechbox, etc.

Anyways, when you put the mechbox back together, did you put the end of the tappet plate in the grooves of the nozzle, or in behind. I think that's what Harley is trying to say. Tell you what, shoot your gun (unloaded of course, and barrel cleared) with yoru finger on the end of the barrel, and see if it's good air coming out or seems weak. Put it closer, like 1mm away and see that way. I wouldn't recommend putting your finger tight on the barrel though, but having dealt with plugged barrels enough because of torn hop up rubber or lack of lube, it won't hurt to do it a few times.

[The Madcap]

well there is air comming out but it feels more of the weaker variety. I have also noticed that when the .12 bbs fire they tend to come out in clumps of 2s & 3s with one sometimes just rolling out of the barrel. I don't specifically remember setting the tappet plate exactly where it needs to be which is seeming more and more like it could be the problem. As I feared, I will have to yet again tear the damn thing apart. It is comforting to know that my AEG frustration is just the tip of the iceberg. Still it feels good getting to learn about these guns and mechboxes, getting plenty of practice at tearing them apart & putting them back together. I should be able to help out my friends if their lazy asses ever decide to buy guns. Thanks CDN. I'll post back after I tear it apart.

[CDN_Stalker]

Did you set the stud on the sector gear (the one that moves the tappet plate back) as close as possible to the tappet plate (without pulling back the tappet plate at all) with the bevel gear firmly latched into the anti-reversal latch? Some people call it timing, others poo-poo the concept, but I've expereinced enough times setting it incorrectly (even a tooth one way or the other away) screwing up, to know that it has to be set a certain way to work right. Sounds like that might be a problem as well. With your anti-reversal latch set in the notch on the gear, have your stud on the sector gear about 0.5mm away or touching even. Make sure the tappet plate is full forward in the mechbox (most likely it's touching). If you set the sector gear too far clock-wise, you might find (at least 3 separate times I've done it) the piston jams full back and won't release until you take the mechbox apart. Set it a bit too far counter-clockwise, it presses the tappet plate rearward a bit, causing it to not go full forward enough into the hop up sleeve to give good sealing, making some shots come out normal, others will fly out the barrel and drop to the ground within 10-15ft. (Feel a debate coming on, oh well, experiences vs. experiences hopefully, and not experience vs. 3rd hand opinion.)

[mcguyver]

You guys are way off the mark. Remove your inner barrel and hop chamber from the gun. Turn the hop-up completely off. Put a bb in the chamber and blow. If it comes out of the barrel with barely a puff, your hop rubber is fine. If it takes any kind of effort at all, your hop rubber is either swelled (wrong rubber + wrong lubricant = trouble) or installed poorly.

The notion of gear timing is crap. The first time you pull the trigger, it automatically sets itself. Pistons only "lock back" when they're installed poorly and the guy putting them in let's it twist a bit and it no longer runs in the guides properly. It happens all the time, but if you fail to catch that and let it go, it will come back to haunt you.

[The Madcap]

Thanks for the feedback mcguyver. The gun really did work fine before I dismantled it. I took it apart to change a spring & to see for myself what upgrades it actually contained (not fully trusting the seller). I was careful to remove the mechbox each time so as not to damage the hop up chamber at all. I suppose that I could have but it didn't seem like it. Anyhow, my experience w/ these guns is quite limited so perhaps I need to check on this. Assuming that the piston is in the guides properly (which it is), are you saying that there is no reason to tear apart the mechbox yet again? i just don't want to have to if I don't.

[mcguyver]

No don't tear it apart yet. Try the bb down the barrel test ands see. Too many times I've seen guys (even experienced ones) freak out over the gun being jammed or not firing and want to do a teardown, when all it is is the hop-up. Try that first.