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

[Stevobeavo]

I had teeth snap off my spur gear on my specna edge. I've ended up getting a new zci shell from ak2m4 with all new Gears and internals 

 

[Dan Robinson]

I had teeth snap off my spur gear on my specna edge. I've ended up getting a new zci shell from ak2m4 with all new Gears and internals 

Was looking at those this evening... The boy wanted to do a DMR build, so might use that as an excuse to learn how to build a gearbox from a donor seeing as we have a perfectly good aeg box in it now.... Just change spring and boxes out to change roles.   Then of course need to learn more about motors and interactions with voltages. 

God damn this hobby ?

 

[Dan Robinson]

Little update, Cage were running silent so I bought my own set of 16:1 gears and had a crack at rebuilding and shimming. 

Took a few goes and lots of YouTube but I think I finally cracked it (so to speak). 

I don't know what I did differently so can only assume the missing teeth on the old cogs were the reason for gearbox locking. Pew number one is now back together and cycling nicely with a decent punch of air coming out of the barrel.  Can't really test it properly though at this time of night. Plus I should really put some grease on the insides.  But it appears that I have graduated to Junior Tech First Class. 

Have some proper silicone grease coming tomorrow so hopefully will get it rebuilt following a successful garden test in good time for next game day on the 19th.

Will upload a video for you guys to assess the sound as best as can be done to see how it is.... I still have trouble discerning what's acceptable and what is good when it comes to these cheaper gearboxes.  I'm still envious of some guns who sound like the gears are running on silk, but I'm guessing they're 4 figure pews.. 

 

[Dan Robinson]

Well I think it doesn't sound too bad... 

 

[Rogerborg]

Congrats on the working gun.  You are now over qualified to post on Reddit.

Hard to tell from a video, but I'd have a fiddle with the motor height and see if it'll hush down even more.

 

[Dan Robinson]

Just had a successful mag dump into a bucket.  Don't have a chrono, but feels good. 

Question now is do I have the guts to strip it back down and add some greese.  I guess it comes down to how likely my previous problems were down to missing teeth on the gears.

 

[RostokMcSpoons]

Just had a successful mag dump into a bucket.  Don't have a chrono, but feels good. 

Question now is do I have the guts to strip it back down and add some greese.  I guess it comes down to how likely my previous problems were down to missing teeth on the gears.

@Rogerborg has suggested to me spooging some chainsaw oil into the shell and silicon spray up the nozzle as a good way of lubricating a gun without doing a gearbox opening.  The question becomes... Which chainsaw oil is best for the job?  And where to spooge exactly?  

View attachment 100909

 

[Rogerborg]

a good way of lubricating a gun without doing a gearbox opening.

I've checked with him, and he says it's not a "good" way, just a way.  He reckons he mostly did it because it would make Skylaar on Reddit go shouty-crackers, but it hasn't caused any problems. Any fairly heavy oil should do, through any holes that give you access to the gears, used sparingly - he just had some low fling chainsaw oil to hand.

 

[RostokMcSpoons]

I've checked with him, and he says it's not a "good" way, just a way.  He reckons he mostly did it to because it would make Skylaar on Reddit go shouty-crackers, but it hasn't caused any problems. Any fairly heavy oil should do, through any holes that give you access to the gears, used sparingly - he just had some low fling chainsaw oil to hand.

When you say 'him' I'm guessing .... Luke?

 

[Dan Robinson]

Well I thought, sod it, I need to learn.  So took it apart, being careful with the shims (drew the gears on a piece of card, and marked the top and bottom, placing the shims accordingly. 

Gave a modest smear of silicone grease on all the contact points. Then decided to augment the piston oring.... Which was looser than a wizard's sleeve.  So just to piss Mr Luke off, I carefully (because I'm a plumber and spin this stuff out of my rear orifice) wrapped ptfe in the groove of the piston Under the oring. 

Now hear me out.... Nothing pisses a decent plumber off more than seeing ptfe on the threads of a fitty.  It's retarded.  However, carefully wrapped around the pipe BEHIND the olive is a good way to fix a leak. 

This is what I did to the pew pew. 

How effective it is we will see at chrono next week. 

All reassembled and I'm very pleased with the sound and feel.  So hopefully the hop uniit, bucking and the rest of what is essential to slinging small plastic balls at random strangers is on good order. 

Also rather pleased that I managed this all in the space of 90 minutes, with distractions.   That sodding anti reversal latch was the worst.  Especially when the trigger pinged out as well taking its spring with it. Definitely going to get some of those clips! 

 

[RostokMcSpoons]

I don't know much but I know the o-ring is designed to be loose fitting ?

 

[Dan Robinson]

I don't know much but I know the o-ring is designed to be loose fitting ?

Balls.... Guess I'll have to take it apart again ?

Do we know why it needs to be loose?  The air seal was shyte between Piston and cylinder head. 

Now pondering whether the gearbox will take 11.1v batteries too LOL. 

 

[RostokMcSpoons]

I'll let an expert comment tbh, I should've kept my fingers off the keyboard.  I should have said 'believe' rather than 'know'

Don't do anything until someone else tells you to.

All I can say is, all the piston heads I have dealt with have been the same, with the loose o-ring

 

[Dan Robinson]

When I say the seal was rubbish, I'm looking at it from my professional perspective of leaking natural gas and things going boom. 

To my mind there should be no way of pushing the cylinder all the way down.  Which certainly wasn't the case.  Although there was a definite resistance.  

I was wondering what the holes in the piston head were for though. 

Edit*

Might have found the answer... 

https://youtu.be/RCUB6_JS76Y

 

[EDcase]

Yeah the O-ring on the piston is meant to be a bit loose fitting in its groove.

When the piston moves forward in the power cycle the air in the cylinder compresses and goes into the holes in the piston face.  This expands the O-ring to make a good seal without binding.

Then on the return stroke the loose O-ring allows for air to pass easily and not restrict movement of the piston backwards.

 

[Dan Robinson]

Whelp.... We'll see how it goes on the weekend LOL.   Bloody airsoft... We complain about the tolerance on one hand, then rely on sloppiness with the other ?

 

[RostokMcSpoons]

View attachment 103607

 

[Paul E H]

Hi,

I rebuilt  a v.3 gearbox last year and had some similar issues.

Compression lightly  silicone oil piston ring and bore it'll help you shouldn't  be able to push the piston down much if small nozzle is covered, then do same with the  bigger nozzle (one attached to tappet plate) that feeds bbs and seals in hop. Should be no difference in compression again a little oil between nozzles as an o ring built inside 'feed' nozzle. If you compression is OK then good news.

Manually move gears and check tappet plate is moving smoothly and nozzle goes forwards and back when contacting the cam on the gear. It's important that the timing is correct between compression and nozzle position it's easily set by moving cam gear to the point it engages on piston teeth there are vids on this that show what I mean.

I found my feed issues down to nozzles too short by 1mm! And flexing tappet plate/worn cam end.

Also the barrel (G36c) spring was weak and not pushing/holding hop back in place so not getting a good seal on nozzle/hop.

I tried a whizz bang cnc'd alloy hop for G36's and it wasn't suitable at all and caused misfeeds and poor compression. I've since found a decent hop unit. There are tiny differences between brands whilst most are TM copies it doesn't  mean parts are interchangeable without modding or just don't fit!

Nozzles. Check length with accurate measuring tool. Mine. Was 22.4mm. I got a 21.5mm and it looked the same but just didn't work.

The timing of compression/nozzle and decent right length nozzle is vital. And dont forget the hop and its function and things like springs are working ok. I spent a fortune rebuilding as parts promised to fit or improve didnt!

stick with a decent brand or oe parts. I managed to get an oe upgraded piston with metal teeth stuck with laylax and shs for all other parts. Laylax only company who made an identical  type of nozzle and this massively improved compression.

Sorry its a bit of a brain dump. I'm an armature with some engineering experience from motocross and 'performance  car' diy  fix it myself days. The v.3 gearbox drove me to despair but got there. But, don't assume hop is OK may be time to replace the rubber and nub and that the nozzle is making a good seal on the hop. If no seal and misfeeds imho likely nozzle not travelling far enough or hop damaged. 

PH

Good luck.

 

[Paul E H]

That blue plastic cam on the tappet plate  gear is a timing delay plate. Was it fitted from new or do you know why its in there?

 

[Dan Robinson]

Thanks for all the information.  I am thinking about a new nozzles as there doesn't appear to be an O-ring in there, nor a groove for it to live.  I have a micrometre which was a god send for sorting out the packet of shims - although there were a couple that were neither one size nor the other wen compared to the packet listing.

As far as I know the timing delay plate was OEM.  The only other person to work on it was Cage Airsoft, and I think I only paid for a new inner barrel, bucking, nub and shimming.  The new gear set were the Specna 16:1 from Patrol base, so hoping it is matched to the Specna piston.

The spur gear was the only one that wasn't stripped of teeth so I have kept it.  I haven't counted the teeth, but I think it was a 16:1 set in there, so should be OK to go with the other two gears?

Currently trying to resist the urge to by a Chrono now - but with 13 guns between me and the boy, I think I have enough potential tech work in our collection to justify it LOL.

That blue plastic cam on the tappet plate  gear is a timing delay plate. Was it fitted from new or do you know why its in there?