[CM048S] Gearbox not cycling - Piston/spring issue
 

Hello,

It's been quite a few years since I looked at this one, it just kinda stayed in a "ugh i'll do this later" ziploc bag and considering my last thread is from 2015, it has been a while.

The gist of the problem is : Gearbox isn't cycling. Motor connectors get very hot, so does the battery. It jams at what I can imagine is the last tooth of the sector gear, the piston is about 3 shims away from the back of the box, and rotating the bevel gear is met by a blockage. Only way to reset it is to pull the anti-reversal latch and release pressure.

Components :
Stock Cyma V3 gearbox
Guarder SP110 spring
15 Teeth SHS piston (7 steel)
SHS-040 piston head
Short V3 cylinder head
Long V3 nozzle
SHS trigger switch/block
SHS tappet plate
Stock 8.4 1200MAh battery

As far as I know, I haven't ordered any gears, so these are most likely stock.

I've got a feeling that the piston is travelling too far back before release and can't complete the cycle due to some X reason which i'm guessing is the gear has too many teeth? Or maybe the piston. Or maybe removing the spring guide shims (or at least two of them)...

Also yes, I know it lacks some grease right now, I just want to get it to cycle once or twice properly then i'll give it the workover. To give you an idea, the cylinder head is now welded to the cylinder.
And the tappet plate spring, frankly I don't know what happened here, but it is a little mangled and weird looking. Will have to get a new one at some point.

PICTURES!
Attachment 62084

Attachment 62085

Attachment 62086

Any help sure will be appreciated!

If the only thing you changed was the spring and it was working before, I think you should revisit that.

Not to mention pestobanana already gave a good tip back in the previous thread.

So any suggestions as to a similar FPS spring that would be shorter? I could swear i'd done the research and the Guarder was "compatible" length-wise. I mean, I COULD try it with the stock spring just for fun, but it seems to me the piston goes back way too far, or is that normal?

I mean sure, I could just throw in all the stock stuff (if I can find it), but I mean I do have all the fancy new stuff already bought... Sunken costs and all that

There are 16 teeth on the sector gear and 16 (minus one) positions for the teeth on the piston to account for the AOE. I don't believe there is any issue with the number of teeth because they are by design... Unless you intend to short stroke your gun.

In your last thread you mentioned that the piston head was seized... did you ever get that fixed? That WILL affect the ability for the gun to cycle. Sounds like the spring and/or the bearings are too thick and it's binding on them when it's at "95%" compression and pressing against them.

I'd just try swapping the piston head, then springs, etc. and doing measurements along the way to see what's working and what's not with each other.

In general, I think that it should be going all the way back for "maximum efficiency" e.g. you paid for this length of travel, that's how much you're gonna get especially with a non-ported cylinder.

You have a couple of options... each one less and less ideal. Switch to an SHS M90 spring (personally never had a problem with this spring but fps varies between 280 fps or 330). You could short stroke it. Or even cut down the SP110 spring one coil at a time until you achieve your desired results. etc.

I frankly don't remember what I meant by that, I know my cylinder head isn't budging, but the piston head was just fine to take apart, and it seems very thin and just the right size for the spring to sit on.
Attachment 62087

Wanted to be sure its "normal" that it goes all the way back, i'm very rusty at this and my conceptions aren't what they used to be...
Alright, i'll try to find the stock spring for starters and see how that works out, then if that works, i'll order a new spring. Everything started with replacing the spring after all.
As for the cylinder, if ported is worth it, I might as well buy one from SHS while i'm at it.

So apparently there's ported pistons now. Worth it?

And I definitely will try an SHS spring.

There's a chart somewhere that matches the port position with barrel length somewhere. Basically barrel length dictates how much air is "needed" to push the bb out and the port reduces the need for how far the piston needs to travel to achieve that volume of air.

If you're running a shorter barrel then it's worth looking into if you're doing any kind of high speed setups/short stroking mods otherwise it's perfectly fine stock.

Just get your gearbox cycling normally again before doing any other upgrades otherwise it's just a waste of money.

Well I tried the original spring, which is shorter, and it still doesn't cycle. I attached pics for reference.
Attachment 62121
Bottom spring is original
Attachment 62122

Unrelated, the tappet plate now rubs on the trigger slider connector thingamajig and catches on the spring but that shouldn't prevent cycling.
Attachment 62120
Sorry about the trash focus, that's about as close at it goes.

Really thought trying the original spring would cut it.
Been a busy month, just got some time to mess with it.

Quick test for you to try, put the gearbox back together with no spring, cylinder or anti-reversal latch and manually move the piston to the rear to see if it get tight/stuck at rear.

I have had off spec SHS pistons cause issues in my VFC V3 gearbox's in the past with locking up, they would literally get stuck at the rear of the gearbox. Going back to stock or another SHS/other brand of piston would fix the problem.

May or may not help with your situation but definitely something worth trying.

Could have been, but no luck. It does have some left to right slop but within the cylinder it should be enough not to wobble anyway. I didn't feel anything catch or prevent it from sliding as it should.

The thing is that the new SHS piston is deeper than the previous original piston, so there should be more room for the spring to compress, but it doesn't.
This motor has been barely used since I got this thing, so I doubt it's the problem, but who knows