MP5 Mechbox unwinding ->lockup
 

Hello

I posted a week or two ago concerning my recently upgraded MP5.

http://www.airsoftcanada.com/showthread.php?t=31667

After that upgrade - pdi 150%, torque up gears, bushings, shims, metal bb spring guide. - I decided to order a new Guarder Nozzel and Tappet Plate.

With my new found confidence in upgrading my mp5, i figured that changing 2 parts would be a sinch.

Well, Got it all back together, didnt touch anything else to my knowledge, and it wouldnt shoot the bb's the mag pushed into the chamber. I figured it was something to do with the new guarder tappet plate, or my hopup got messed up while reassembling the gun. (maybe my barrel moved in/out of the hopup unit?)

It would fire if i inverted the gun, removed the mag, and shot in single. Then i could insert a mag, and fire on full auto/semi np, although it didnt sound quite right/not the same power as before.

So i tore the gun apart again. and after reading that somepeople has to dremmle down their tappet plates, i decided to compare the gaurder to the stock.

The guarder is far wider at the tab portion where the half gear engages it. (looking from top down, its wider.)

So i put my stock tappet in but kept the guarder nozzel to narrow down the problem.

Well. Put it back together, checked timing to be "locked and at 1 oclock".

Fired and Voila! it worked, for about 10 shots before the Mechbox started to unwind, and with more trigger pulls, the whole gun eventually locked up.

Tore it apart again. The piston was cocked right back. :S Opened very carefully and let it unwind.

So for the next 3 or 4 attempts (build up, test, breakdown again), my friend and i tried to figure out what was going on with these gears.

We tried multiple timeings (half gear pin at 3-even 4 oclock) with the latch locked each time.

Still same problem. I then placed the original nozzel back in. No change.

Now instead of cocking the pistion right back and locking up, it cocks half way, and locks up. i also found this pins the tappet and nozzle right back also at the same instant. all 3 will stay that way untl i opened the case.

Any idea what is going on here? I had this gun working great a few days ago, then i change 2 parts and all of a sudden i cant get the thing to shoot. Im now on my 5th or 6th attempt, having stripped 2 of the screw locations on the top of the mech box already from tightening and loosing so much lol.

Any ideas would be much appreciated as to how to properly set this timing thing up, if that is infact the issue.

We figured the anti reversal latch wasnt locking with the grove on the bevel at the right instant, causing the whole thing to wind back and lock with the pistion just as it starts to decompress.

my dad is bringing back a p90 for me in the next few days from asia, so this mp5 will become my upgrade learning gun, im not going to touch that p90 lol, maybe except for metal bodies

Thanks

Corey

Tried again, same thing

to unstress the spring though, i used some needlenose plyers and pulled on the reversal latch. this unwound the system

im able to turn my bevel gear by turning its bushings, and found that the latch isnt even engaging with the groves on the bevel gear. i can feel the latch pass over, but when i turn in the opposite direction, it doesnt lock up, just clicks over the top of the grove and continues on.

Could all of this gear timing stuff be caused by the antireversal latch not working properly?

It seems to be working on and off. I can turn the bevel until the sector starts to pull the tappet plate back, then i turn a bit further and release the bevel, sometimes it catches the reversal latch, sometimes not.

is there anyway i can get its spring to tighten up a bit so it has the strength to engage with the bevel gear?

thanks

corey

Maybe time for new anti reversal latch spring?

yeah, but anyway to stretch this one out again? ill give it a try but if someone has experience with how well that works that woould be great. id hate to pay 25 bucks shipping for a 2 cent spring

better $25 for a 2 cent spring, then $80 for new gears......

cant beat that logic lol

Problem still exists

Tried stretching the spring by bending back the end of spring that presses up againest the mechbox. definately helped push the latch in place while i was spining the gears by hand.

but once i got the receiver back on and test fired, the pistion immediately locks up half way, and sometimes all the way back :S at best i can get 1 shot out on semi-auto before the thing starts to lock up. with every trigger pull is gets worse and worse till nothing moves

any tips on why this is occuring? i though it could have been the reversal latch, but i think thats corrected now.

I've read that somepeople believe in gear timing, other dont. at this point im willing to try anything.

i've been dry firing the gun, with only the receiver attached to hold to motor on so i can see the nozzle and piston move in the cylinder vent.

I found my MP5 would have it's anti-reversal latch overrun (unwound when I'd stop shooting) when I bought a second PDI 150% spring and found it too long (6 5/8") and stiff compared to my original one. I cut off a few coils, installed it, the gears and piston would unwind after every few shots. I took the spring out, threw it as far as I could (waste of $20) and put my good 150% back in. Haven't had the problem since. Remember my pressuring you to get rid of that spring and buy a good (NON-PDI) spring that went through quality control? ;) See why now?

lol

yeah i know :rolleyes: I did measure it like you suggested and its the long one - shiney black.

whats bugging me though is that it was working well before i tore it apart the second time to put in the tappet and nozzel. :S

i ran about 20 low cap mags through it before i put them in and didnt have any issues like this.

doesnt make sense

corey

how are guarder springs? or do you guys recommend systema? thx

Just a wild idea, but are you for sure your battery is fully charged?

hum.....

well, i charged it last night before i took it apart the first time. havent charged it since. ive had it apart and backtogether about 10 times now lol, getting old. ill be able to do this blind folded soon.

ill give it a quick zap when i get off work, dont have the charger with me right now lol

Corey

I've had really good experience with the Prometheus springs, they compress alot easier than my GOOD PDI 150% spring, and still put out well. Depending on your goal fps, as well as what other upgrades you want to put in, I'd recommend the Prometheus 110SP, in a relatively bone stock MP5, it should give you around 330-340fps. Add in a bearing spring guide and tightbore barrel, that should set you around 350-360fps, more than enough for outdoor games using 0.25g BBs.

Does the gun work with the stock spring in? If it does I would stop mucking with the anti-reversal latch and try a new spring...

Hey Guardian

I was just thinking that, so i went home and grabbed the stock spring to try.
I also charged my battery.. turns out that is took about 550 mA ! its a 600mA battery, so it was pretty dead which really surprised me.

Thanks for the info Stalker, ill give that one a try. I do have the metal spring guide, torque gears... so that combo should go pretty good from what ive read

Im going to try one last time with my crap pdi 150 spring with my recharged battery and see if i can get this thing to crank over. if not, ill try my stock spring

will get back to you soon

Corey

Well, illusion turned out to have the winning tip lol, charged battery, mech box works perfectly again lmao

It may have been failing do to the antireversal latch the first couple of times, but by then the battery was getting dead (far sooner than i would have expected) . I'm definately going to try a new spring, ill go with prometheus i think, stalker.

Now to completely reassemble the gun and see if the BB jam problem has dissapeared by putting my stock tappet plate back in, after all, thats what started this whole mess lol. still have my guarder nozzel.

Seems like the guarder tappet is made for all the version 2 mechboxs in one. not specifically one or the other. so it didnt seem to work at all with my mp5 ras. would have to grind in down to match the stock one, but even then, its not perfect.

Thank you all, you've all been really patenient with me, especially with this thread lol

Corey

now why is it that neither of us thought about the battery?
we thought of almost every other sutuation from gear ratios to the anti reversal lock and spring. man... half of me hopes its a dead battery and the other half wishes its not for the simple over sight we may have had.
oh well im just a noob to this realm:P

your friend malachite


"never argue with an idiot, they will drag you down to their level and beat you with experience"

For the upgrades you mentioned, you will need a larger battery to power them. 1700 mah atleast, if all you have is a 600mah, its no wonder you dont have enough power to turn the mechbox completely over more then a few dozen times.

If you are going to order some parts, buy an Intellect 8.4V 1400mAh mini. I bought one for $22US from UN Company, and use it in my secondary MP5 (has the Prometheus 110 spring in it) and it rips fast (much faster than my MP5 with the 150% spring and 3300mAh battery!) and lasts a quite a while between charges.

Battery eh? I should have thougth of that as I had same problem with my AK, my buddy took it home- charged battery and had no problem:) I still have the egg on my face from that one...

I didnt realise there was a 1400 8.4v mini, thanks Stalker

I was actually at the local electronics store a week ago looking for some cells to build a new pack. They were bringing in some AAA, NIMH 900 mA cells. i'd get 9 of these, 8 in series, 1 parallel. So id hope to make a pack with 9.6v and 1800 mA for the same size as a mini

Any thoughts on this set up? or should i stick with 8.4? Im also tempted to stick a lipo pack in, i have a bunch sitting around the house not getting used, ive read that some people go with 7.4 v and have okay rof. is 11.1 too much?

Hey chris, welcome to ASC

thanks again

Battery might be too small to sustain that spring for very many shots too.


I had a PDI 150% in my M4, the PDI that broke TWO ****ing mechboxes in less than a month. That spring is now *somewhere* in the Foxden as I threw it as far as I could in there.

Back to the point was, I'd get maybe MAYBE half a mag of rounds through it before the battery died. Then we re-shimmed it and cleaned it out and I'd get a mag but it'd still drain that battery. Battery was old and was dying so I got a new 3300Mah battery and never had an issue with it, until it broke the second mechbox by litterally blowing the front end of the box off. It was the delta ring assembly holding the thing together really.

Hey Dracheous

Wow, yeah im definately going to lose this pdi spring and go for a prometheus or systema 120

As for my battery, the 600mA has been doing fairly well, dispite the new spring. while testing it, i'd go through about 5-6 mags before i really noticed a difference in power. thats why i was so suprised when i recharged last night.
I guess that trying to turn the motor over while the whole thing was locked up sucked it dry lol

corey

Don't suppose your fuse blew, eh? Trying to make the motor turn over the locked up mechbox makes the motor work harder, so it sucks more current, and if you had a 15A fuse in there it'd blow. 20A-30A would probably handle it, but the battery would get hot trying to feed the motor.

nope, took your suggestion and put at 25 amp fuse in from my first upgrade attempt :D

Good man! :D

man sounds like that bad boy is giving you grief Corey lol...hope you can get it out to a game with us soon lol (hopefully it isn't snowing like crazy again) :P

Hey pip,

yeah, looking nasty here in nanaimo, my car will have trouble making it up that hill if it doesnt melt by then lol :S

just ordered that intelect 1400 8.4 mini :)