CYMA MP5 has died of death after motor adjustment - any ideas?

[pyromancer6]

Hi all,

Just following up from my previous profile post bitching about my guns being broken - I was adjusting the motor height on my completely standard CYMA High Cycle MP5 because it was sounding a little screechy and ended up pushing the motor in too high, to which I then lowered it back down to near-about where it used to be.

But, the moment after doing that and ever since it produces a horrible screeching sound on firing and I was wondering if anybody here would have any info on what it could be before I start ordering a bunch of replacement parts that I might not actually need.
 


Img 5572.mp4

 

If it helps - I tried plugging in the motor without it being within the grip and it seems to be spinning freely - what could be causing the lockup inside?

 

[Sewdhull]

Pull the motor out and examine the gear on the end.

if it looks ok, put it back in and readjust it.

Id pull out the grip and box too. You may have a chunk of gear in there perhaps

 

[pyromancer6]

Pull the motor out and examine the gear on the end.

if it looks ok, put it back in and readjust it.

Id pull out the grip and box too. You may have a chunk of gear in there perhaps

Should've mentioned that in the OP - the motor pinion seems completely fine. No matter how it's screwed in it still makes the same god-awful sound. I was thinking the cut-off might be knackered but I wanted to put this thread out for feelers and a second opinion

 

[gavinkempsell]

Take the gearbox out and give it a rattle, move the gears with your finger and feel for any roughness as they turn.

as a last port of call open the gearbox and check... if you're comfortable doing that.

 

[pyromancer6]

Take the gearbox out and give it a rattle, move the gears with your finger and feel for any roughness as they turn.

as a last port of call open the gearbox and check... if you're comfortable doing that.

Fully open to taking the thing apart - was going to upgrade the compression and do the usual ak2m4 goodies like I did with the UTR & M733 that I'm currently working on, just wanted a second opinion on the things that it could be (appreciate the input on the profile post and here btw) so I could order them without ordering extra things I might not need in the end. Will give that a try though - moving the gears manually to see where it gets stuck might indicate what's actually causing the lock-up

 

[Skara]

Sounds like your motor is too low, so it just barely engages the bevel gear (read it's chewing it away).

Whenever you adjust the motor height, you should:

a) plug the weakest battery you own to minimize emotional collateral damage;

b) start with the motor HIGH, that way should anything happen it'll just stop instead of shredding something.

Keep adjusting (read unscrewing) by a quarter turn at the time until the sound is crisp/not as scratchy, if you keep going you'll hear the sound change to a low-ish note of scratching, this means you've gone too far and the motor is now too low. Find the sweet spot in the middle.

I was thinking the cut-off might be knackered

Cut-off is not near the motor, it's next to the trigger and doesn't affect noise.. You probably meant the anti reversal latch, which engages the bevel gear, but that generally doesn't do anything apart from wearing itself out at a stupid angle.

A worn anti reversal is recognizable because every time the gun stops firing you'll hear the gears slowly spin in reverse under tension from the main spring and the next shot will be a double feed.

 

[pyromancer6]

b) start with the motor HIGH, that way should anything happen it'll just stop instead of shredding something.

This is what I started with when I was orginally attempting to adjust the height pre lockup - it was when lowering it the issue happened.
 

Keep adjusting (read unscrewing) by a quarter turn at the time until the sound is crisp/not as scratchy, if you keep going you'll hear the sound change to a low-ish note of scratching, this means you've gone too far and the motor is now too low. Find the sweet spot in the middle.

Thought it'd be easier to just compile everything into a video.

https://streamable.com/z93517

One thing to note is that the motor doesn't want to drop into place/spring freely without the baseplate on which I'm assuming means either the ARL is being a bugger or the gears are that jammed that there's either a piece of gear jamming the action or one of the bushings/bearings has exploded. Come to think of it - when it first happened the fire selector became awfully stiff (spur gear or spur bushing?)

Regardless - I've ordered a few parts and I'll crack it open when I've finshed the other pew that's in bits to see what's actually going on. Appreciate all the input

 

[pyromancer6]

Got around to taking the thing apart, even though it's roughly several thousand degrees in my room at the minute.
 

That'll do it! Not looking forward to putting this thing back together, seeing as it's going to be my first non mosfetted, non qc spring gearbox going back together ?

Think it'll buff out? 

 

[Colin Allen]

10 hours ago, pyromancer6 said:

Got around to taking the thing apart, even though it's roughly several thousand degrees in my room at the minute.
 

A quick spray of WD40 and it will be good to go.

 

[pyromancer6]

A quick spray of WD40 and it will be good to go.

Bit of PTFE tape and a drilled nozzle should do the trick mate ?

Anyway, gave it a clean to get the remains of the bearing and terrible blue alien goop out and was suprised to see the parts are all in good order. Wasn't expecting to see one of those silent style piston heads but it's getting the ak2m4 XT air compression classic regardless so I'm not going to worry about it. Seems to have better internals than the CM.009D M733 that I just did, with a full metal rack, 12:1s etc. It's just not the quick change type unfortunately, so that's going to be a pain in the arse to put back together considering I've never done one before. Still, interested to see how a little re-shimming and proper grease quiets this thing down.

 

[pyromancer6]

Another one - turns out because it's an older gearbox it's either 6mm or 7mm bearings, not 8mm. Gutted. Will have to order some new ones so unfortunately won't be using this pew tomorrow

EDIT:

One amazon payment later:

7mm. Would've been nice if the info was anywhere but I probably just missed it. I was looking at the current listing for the CM.041J but that's got an actual quick change gearbox and 8mm bushings compared to my older version here. Can get some ordered now at-least and hopefully get this show on the road.

Still desperately looking for a replacement cocking handle if anybody has any pointers - trust me, I've tried everywhere. I'm getting desperate at this point.