Gearbox Locking up Gg Cm16

[Funnyhat29]

Hi all,

So a couple weeks back I decided to brush the dust off my g&g cm16.  I have had the gearbox open before but decided I'd open it up, give it a clean and re-lubricate it, all was good, re-assembled and test fired.  But during the process of re-assembly I had noticed the airseal was shocking, so ordered a new air nozzle and o-ring for my piston (was in two minds about going down a large upgrade route but decided for the cheaper option).  A few days later my bits arrived, quickly test fired a couple times before disassembling to fit new parts, and the gearbox locked up.  Dissassembled and could see through the cylinder port that the piston was locked to the rear.  Did some shimming for the first time and have also been getting to know the inside of my gearbox a lot more (sounds intimate, I know).  

 

I re-shimmed and assembled the gearbox without piston, spring, cylinder etc. and attempted to turn the gears with my finger.  I noticed that the cut-off lever appeared to block the sector gear on a rotation, exactly at the point that the piston would be pretty much at the rear of the box.  I tried a few adjustments and all was good, gears spun freely, no sticking point.  Re-assembled and again the piston locked to the rear.  Thought maybe my shimming job was potentially too tight, despite there being free up and down wiggle room, so removed a 0.1mm shim from each gear.  Again gearbox stuck to the rear.  I took the motor out, and spun the bevel gear with a screwdriver, after a few turns the piston shot to the front.  This leads me to believe there is no physical block on the gears or pison (I can rule out the cut-off lever etc. as it is all standard internals minus the air nozzle).  I thought the battery could be quite flat as I gave it a few hours charge when I initially went down this rabbit hole but never fully charged it.  

 

Anyway enough of my waffling,  the battery is currently on charge, and going to wait for it to recharge fully.  If I am still getting gearbox lock up, after this, what would be people's recommendations I try next?  

 

Thanks  

[DerDer]

What kind of battery are you running it on? An underpowered battery can sometimes cause problems. 

[Funnyhat29]

3 minutes ago, DerDer said:

What kind of battery are you running it on? An underpowered battery can sometimes cause problems. 

it's an 8.4V NiMh, it's a 6 year old battery, was working good about 6 months ago after a full charge.  I am leaning on this being a flat battery issue but just wanted to see if there was anything else obvious I was missing.

[DerDer]

2 minutes ago, Funnyhat29 said:

it's an 8.4V NiMh, it's a 6 year old battery, was working good about 6 months ago after a full charge.  I am leaning on this being a flat battery issue but just wanted to see if there was anything else obvious I was missing.

Would try another battery. Even if you can get a loan of one to establish if it works any better. 

[Skara]

Try with a fully charged battery (and get some LiPos ffs, they're cheap now , it's not the early '2000s anymore)

 

With that out of the way, have you tried spinning the gears with the gearbox fully tightened before dropping everything else in?

It is a common mistake with "newbs" where the shimming seems perfect but then ends up being super tight with the two half shells screwed together, don't worry, we've all been there. Plenty of guides online on how to shim.

 

Since you're running NiMhs I'd say the weak battery + weak motor (assuming it's a bog standard CM16) is what causes the lockups.

 

When that dinosaur of a battery is charged, and if it still locks up on semi, try firing in full auto (removes the COL variable as it will not engage the sector cam anymore). If it locks up in full auto, you probably shimmed too tight.

[Funnyhat29]

11 minutes ago, DerDer said:

Would try another battery. Even if you can get a loan of one to establish if it works any better. 

 

Unfortunately nobody near me I know has one, and moving into tier 3 next week

 

10 minutes ago, Skara said:

Try with a fully charged battery (and get some LiPos ffs, they're cheap now , it's not the early '2000s anymore)

 

With that out of the way, have you tried spinning the gears with the gearbox fully tightened before dropping everything else in?

It is a common mistake with "newbs" where the shimming seems perfect but then ends up being super tight with the two half shells screwed together, don't worry, we've all been there. Plenty of guides online on how to shim.

 

Since you're running NiMhs I'd say the weak battery + weak motor (assuming it's a bog standard CM16) is what causes the lockups.

 

When that dinosaur of a battery is charged, and if it still locks up on semi, try firing in full auto (removes the COL variable as it will not engage the sector cam anymore). If it locks up in full auto, you probably shimmed too tight.

 Yes very true it is not 2014 anymore  yeah tightened everything with no only gears and a couple bits were stiff so removed some shims previously, will definitely wait for the grandad battery to charge, if it solves it will definitely invest in a lipo 7.4 and deans connectors!  I will also bare the fully auto trick in mind if it continues to lock thank you!

[DerDer]

Fair enough, yeah timing is dreadful.

 

The best can suggest is to fully charge the battery. Then try a magazine or two to see how the shimming sounds.

Pretty much as you said.

 

Black Friday weekend might be a good chance to get some Lipos and a decent charger. Would recommend just ordering from the UK. Postage time abroad are glacial at the moment.