V2 Gearbox Help

[Nimsay]

Hi all,

I've been trying to solve a problem with my V2 for a few days now.

Pretty confident at disassembly/reassembly but still can't troubleshoot why it won't cycle properly.
Here's the latest stage it is at, daren't pull the trigger anymore

Any ideas would be helpful.

 

Thanks

[Asomodai]

Uh. Wow it almost looks like you have put the spring in front of the piston rather then inside it! No help sorry  

 

Are the gears making contact with the piston correctly? AR latch installed correctly?

[Sitting Duck]

2 hours ago, Nimsay said:

Hi all,

I've been trying to solve a problem with my V2 for a few days now.

Pretty confident at disassembly/reassembly but still can't troubleshoot why it won't cycle properly.
Here's the latest stage it is at, daren't pull the trigger anymore

Any ideas would be helpful.

 

Thanks

video0.mov

 

Your piston now has no teeth I reckon....

It seems to be say retracted about 12 out of 16 teeth on sector gear

(back of piston is near passing inspection window)

BUT it ain't moving no more, yet drive chain is spinning etc...

 

If stock piston then it has begun shredding teeth = fucked

What gets me is why piston hasn't flew back to cylinder head after shredding ???

(I mean after sector chews up stuff it should release & fly back)

 

So me thinks it got jammed in that position, still jammed and toothless

 

My guess is that is a Cyma V2 gearbox with its V3 spring guide

(and funny safety lever that needs unscrewing to open box)

clear plastic nozzle etc.....

 

yeah pretty sure that is a slightly qwirky Cyma from a CM 51X range

but that piston is fucked is my diagnosis

 

Hard to tell if piston twisted, doesn't look it at first glance

but something got jammed & shredded etc....

so piston is very likely shagged

 

seems to be running quick, but hard to tell from shredding teeth noise

what did you do - run it on 18v or something ???

stock it would shoot say 12~13 rps on 7.4v

or say 20 ish on 11.1v - so stock wise unlikely to hit PME

unless you dropped a very quick High Speed motor and ran on 11.1v

 

Best bet, is list just wtf you have done - full info btw

(hate it when you start a diagnosis thinking XYZ, then after a while more info reveals

it is a totally different issue that was not mentioned beforehand - grrrrr)

 

take pics, be honest and heed good advice

or send it to Neg Airsoft or other tech if you are not sure

[Sarky]

Take it apart, remembering to hold the spring in place before you seperate the 2 halves, then search UTube for a V2 Gearbox Video

[AK47frizzle]

You sure you put the spring in?

[Nimsay]

Hi all again, thanks for your replies.
Just a couple of things, yeah the spring is most definitely in and behind the piston! With the spring guide behind that.
@Sitting Duck - it is a shoddy cyma v2 well done! Everything about it you said is bang on, down to the crappy safety screw.

 

Here is the gearbox as is, straight after opening, the piston has since shot back down, so perhaps it was jammed on what i don't know.

With everything removed but the piston, cylinder and cylinder head and the case closed, the piston slides up and down freely.

 

 

 

 

 

Above is the piston in the same orientation as the gearbox picture

Below is the piston on the reverse side, it does have a few small grind marks, which i noticed looks like it has come from the lower section of the sector gear (that connects with the spur).

 

 

I did (and still do) have a lot of trouble with the AR latch as it always pops out and doesn't sit still, but when it's in, it flicks back up as it should.

I have reduced the size of the spring by a coil-length in the past and have searched for a replacement just in case that was the issue, but the website says it has an M120 as stock which must be a load of rubbish as the M120 i bought is far too powerful, looks nothing like the current spring and buckles when released.

 

 

[Adolf Hamster]

could be the spring jamming, i've had that before when changing spring and the spring diameter was just so that when it expanded under compression it jammed inside the piston.

 

as for the ARL magnets are your friend......

[Sitting Duck]

1 hour ago, Nimsay said:

Hi all again, thanks for your replies.
Just a couple of things, yeah the spring is most definitely in and behind the piston! With the spring guide behind that.
@Sitting Duck - it is a shoddy cyma v2 well done! Everything about it you said is bang on, down to the crappy safety screw.

 

 

 

I'm amazed the teeth didn't strip, the piston must have twisted somehow

but play close attention to the actual teeth on piston say 75% along

 

You say you changed the spring ???

 

These China guns have an enormous metal spacer in them by default

(some of them have a "hook" into the spacer like JG or SRC, some don't like Cyma

undo it & bin it, grab a M3 bolt & M3 NYLON LOCKING NUT plus M3 penny washer

 

The Alloy spacer is about 9mm long or 3 x 3mm teeth pitch

which compresses spring effectively 3 more teeth with it in than removed

 

3 x 3 teeth in Short Stroking terms will be 3 x M5 in spring terms (aprox)

or 3 x 16.4 fps - 49.2 fps aprox, so you "could" drop the spacer and expect to lose near 50fps

*** NB very rough ball park figure but somewhere about 40 fps I'd say ***

 

Personally grab another piston if the old one looks iffy

and build it without a metal spacer so spring doesn't compress that 3 extra teeth

 

Or just fit a M100 to M105 spring is easiest option

could cut spring, some do but you need to finish it properly

 

Reckon a genuine M100 & new o-ring if compression is crap on existing piston

(with spacer I mean), is about easiest method but there are options

 

Avoid going nutz, stuff like SHS M4 nozzles don't sit too well on Cyma tappet

tappet is a bit bespoke so has cut outs at side up the front

so SHS tappets need modding or use a Modify tappet plate

(all in all, try not to go too nutz on a Cyma unless you are sad & very bored)

 

Really it is a cheap half decent gun, but don't go nutz on it

 

Removing a spacer on a stock piston will drop the weight of piston

perhaps too much tbh - losing about 7gms so piston is say 17gms

instead of say 24gms - great but you do actually want some weight/mass

 

I would be inclined to drop in a cyma metal rack piston

as SHS pistons might bind in Cyma V2 box at back of box

 

Simple option is to cut one of the m120's and go with stock "spaced" piston

but you'd need to do it really well and finish properly

 

magnet under AR latch - tiny round silver neodym magnet under gearbox as others have said

(cheers @Samurai )

 

 

but don't go too nutz & just use it - good pics btw

 

 

***** UPDATE ****

 

JUST HAD A THOUGHT .....

 

'ere - when you refitted all this together....

 

Did you drop or did it slip

 

That tiny tiny metal disc that adjusts motor height on cheapo guns ???

 

I'm wondering, if the disc slipped off, the motor height dropped

then the box started to wind back the piston a bit without too much stress

then all of a sudden, the strain increases and the motor is too low from a slipped disc

 

The whirring wasn't the piston stripping, but a low pinion munching up the bevel

 

THAT could be what was clunking and crunching and jumping - motor height out

coz the tiny disc slipped off and motor dropped about 1.25mm, failing to mesh properly

 

yeah - more I think about it, that is a possible scenario of how it went pear shape

and sounded/performed real shit

 

yup the more I think about it, either shims fell off bevel and bevel pinion height changed

disc fell off motor altering motor height

pistol grip/plate not fitted correctly - careful plastic threads strip easy on cheapo guns

 

somehow the motor height/bevel pinion altered

which it really shouldn't have, but something changed

 

the bevel/pinion start knocking shit out of each other

(they might be a bit worse for wear now, but not too bad if you just tested briefly)

 

All that, struggling to cycle gun, it reached 75% retraction, but sector never spun anymore

whilst pinion & bevel start fighting, so the sector or gun never cycles

and THAT is why piston was not released as expected coz motor is no longer turning drive chain

 

yup - that is my final summing up I reckon says Ace Ventura....

 

[Nimsay]

Damn @Sitting Duck
Amazing
I'll have to have a good look at all of those aspects in detail next time I'm in workshop mode but that's incredible.
I think the answer is there somewhere.

[Iceni]

2 hours ago, Nimsay said:

Here is the gearbox as is, straight after opening

Answer is right there.

No lubrication.

@Sitting Duck is very right about the Piston and the spacers.

The piston and gears need grease. Without it, the friction of the spring pushing the piston upwards on the slides can and does lock up the piston. It only takes the piston been a little slower due to this and you cause the piston to get picked up partway through the next cycle. All of a sudden the piston is rammed as far back as it can possibly travel then gets crushed upwards.

You lube all moving contact points, Even if it's just a light smear. This includes all O-rings, Bearings, and anything that moves at the points where contact is made.

I suspect the piston is now scrap and needs replacing. It may look good but the pre-engagement will have damaged/weakened the piston and it'll be prone to failures and problems. For the sake of a few £ for a new one from AK2M4 it's just not worth putting back in the gearbox. Whilst you are ordering a piston also order some grease!

https://www.ak2m4.co.uk/internal-parts/pistons/cyma-15-tooth-reinforced-piston

 

https://www.ak2m4.co.uk/internal-parts/grease/super-lube-synthetic-grease-10ml-syringe