Specna SA-C12 CORE not feeding. Now gearbox rebuild.

[Dan Robinson]

Well it looks like the O-ring on my cylinder head has a small nick in it leading to no firing (BBs don't feed properly or only go about 4ft).

The barrel and hop have a good seal and the bucking and nub are brand new, so can't think of anything else that can cause the problem?

So the big question....  What do folks recommend by way of new parts?  and how straight forward is it?  Seems simple enough on looking at YouTube vids, but then it always does.

Tah in advance.

 

[Stevobeavo]

I've just fitted this kit into my specna arms E07. 

https://www.ak2m4.co.uk/internal-parts/gearbox-kits/m4-compression-upgrade-kit

Excellent consistently.

 

[Dan Robinson]

Need to pluck the courage up to open a gearbox now..... Anyone have a goosed one I can practice with? ????

 

[ak2m4]

Well it looks like the O-ring on my cylinder head has a small nick in it leading to no firing

A small nick in the oring generally wouldn't cause it to not fire, maybe a small drop in power.  You're going to have to open it up, could be something super simple.  Open it up, post up some pictures or even better a video.

 

[Dan Robinson]

Will do that... Might have to be done in stages.  Have a mad week with work, plus SWMBO is flying back at silly O'clock Thursday morning so have to hide our arsenal that she doesn't know has built up over the last year ?

One thing springs to mind, is that the gearbox locked up and I freed it by releasing the anti reversal latch through the motor housing...  Pretty sure the problem had already occurred by that point though, and the gun does cycle and operate OK visually with a decent puff of air coming out of the nozzle when the barrel is taken off.

 

[Dan Robinson]

Rightio...

Here is a linky to the video of the pew.  Took the barrel off and fired at a piece of blue roll, and I think it is OK on the cylinder and nozzle end.

Next test was to get a BB in the hop, hold my finger over the magazine receiver hole, then fire.  Got a decent shot off every time.  Leading me to think its the seal between hop and mag - or perhaps, the nozzle and hop?

Have ordered a new CNC hop up from Rocket Airsoft, and whilst I was at it, a new bucking and nub from @ak2m4 .  Double checked the barrel seal to the existing Specna Hop and it was fine.

On a different topic - perhaps @ak2m4can help here - thinking of upgrading the spring in my Rapax do you know what is in there from the factory?  Dude at AWA said he'd changed his to an M110.. Do you have the right on in your shop?

Cheers in advance!

 

[ak2m4]

Sorry not a clue what they put in Rapax from stock.  Best way is to give the current readings together with a pic of the stock spring and if possible thickness measurement of the wire.  Otherwise grab an XT M100 and test and adjust.

 

[Tuton]

Hey Dan, might be the video refresh rate but is the nozzle moving back and forth?

If not it could be damage to the Tappet plate up front or on the fin, the gear sitting too low or the spring has snapped/come off

 

[Dan Robinson]

I was wondering how freely the nozzle should move.  I don't remember it being lose that's for sure.

Looks like the goodies are coming tomorrow so when I get home from work/dropping the Rapax back at the shop because the pistol grip came lose again; I'll take it apart again and see.

I'm assuming the nozzle is supposed to move freely assuming the piston is retracted?

 

[Shamal]

The nozzle should move in and out quite noticeably.

Regards 

 

[Dan Robinson]

Not sure if I'm going in the right direction, but I've changed the hop unit and have much more punch down the barrel, so there was a seal problem of some kind.  But there is still the same feeding issue. 

Not totally convinced by the new hop unit itself though as it came with a small tear on the down-barrel end on the bucking, and the nub lever seems too long as if it was forming its own nub.  So I'll put the maple leaf and omega nub back in the box for now.... Can always trim the lever down a tad if needed. 

Anyway, did a couple of slow motion shots and it seems like the nozzle isn't always pushing forward:

Sorry for the grubby fingers. 

That being said if I cycle the piston with careful use of the trigger, the nozzle is freely moving when the piston is retracted. End of the nozzle looks OK to me too, but then what do I know? 

View attachment 101671

Also have a spring left over that came with the hop.  Presumably for a different type of pew? 

Thanks again for the advice. 

 

[Colin Allen]

The nozzle certainly does not seem to be moving properly.  It could well be a tappet plate issue; it might be sticking in its groove, rubbing on the sector gear or possibly catching somewhere.  It is probably time to take the gearbox apart again.

 

[Dan Robinson]

That's what I was afraid of.... Not done that before so not really sure what I'd be looking for. 

Took my Rapax into the shop in Stevenage this afternoon as its under warranty.... One of the guys in the tech room opened a gearbox as I walked in, only to see a spring shoot straight out of said box and launch itself clean across the room LOL. 

Tried to take a picture of the inside of the cylinder but it's next to impossible. ?. 

Will have a look around You Tube to get some tips. Then I'll call Cage to give it an overhaul. LOL. 

 

[Dan Robinson]

I'm feeling very pleased with myself..... 

Tappet spring snapped.... 

View attachment 101685View attachment 101686View attachment 101688

Now where to find one? 

For reference, and because it should get here in time for the weekend.... 

https://www.ebay.co.uk/itm/314285046327?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=OlkWCNwaRSW&sssrc=2349624&ssuid=tna5mbwtskm&var=&widget_ver=artemis&media=COPY

Now the cat is out of the bag.... I'm thinking new cylinder head as the seal seems a little disappointing. 

FFS what have I started? 

 

[Shamal]

I'm feeling very pleased with myself..... 

Tappet from snapped.... 

View attachment 101685View attachment 101686View attachment 101688

Now where to find one? 

Somebody did say it could be a broken spring.

Halfords do a box of mixed springs.might be something in there which will do the job.

 

[Speedbird_666]

You could trim the broken spring end and bend another coil out with needle nose pliers as a stopgap. I've done that before. It will put a bit more tension on the tappet though during cycling.

 

[Colin Allen]

I'm feeling very pleased with myself..... 

Tappet from snapped.... 

View attachment 101685View attachment 101686View attachment 101688

Now where to find one? 

For reference, and because it should get here in time for the weekend.... 

https://www.ebay.co.uk/itm/314285046327?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=OlkWCNwaRSW&sssrc=2349624&ssuid=tna5mbwtskm&var=&widget_ver=artemis&media=COPY

Now the cat is out of the bag.... I'm thinking new cylinder head as the seal seems a little disappointing. 

FFS what have I started? 

Excellent! Well found.  AK2M4 ships out very quickly and has them in stock as well (https://www.ak2m4.co.uk/internal-parts/misc-internal-parts). 

 

[Dan Robinson]

Somebody did say it could be a broken spring.

Halfords do a box of mixed springs.might be something in there which will do the job.

Yep it was @Tuton, so browny points and extra thanks to him ? 

You could trim the broken spring end and bend another coil out with needle nose pliers as a stopgap. I've done that before. It will put a bit more tension on the tappet though during cycling.

Nothing to lose I suppose LOL. 

 

[Lozart]

Excellent! Well found.  AK2M4 ships out very quickly and has them in stock as well (https://www.ak2m4.co.uk/internal-parts/misc-internal-parts). 

Came here to say this!

 

[Dan Robinson]

Looks like it's going off to Cage anyway. I can't get the damn thing back together without it jamming up.  

Two teeth are missing from the spur gear, and 3 are missing from the Sector gear. 

2 of them were already broken as I picked them out when I got it open.  Not sure if shortening the Tappet spring caused it, but ce la vie. 

Might buy myself a boneyard gearbox to practice with instead of my main AEG's ?.