M4 not firing on semi.

.22 Lover · 08-03-2014 7:12pm #1

Hellow.
Ive recentley had to change to a new gearbox shell beacause my previous one cracked it would fire perfectly in semi and full, auto after new contacs and cut off lever.I have removed the gearbox ant tried to fire it on semi outside the body so the selector switch and plate is not the issue.
SHS 16:1 gears
SHS high torque motor.
one of biz 96's AB mosfets
G&G trigger contacs
All in D'boys reinforced shell.

the previous shell was A&K i think ive tried 3 diffrent used cut off levers with no sucesss.
Is there anything else im missing?

matty1994 · 08-03-2014 9:06pm

.22 Lover wrote: »

Hellow.
Ive recentley had to change to a new gearbox shell beacause my previous one cracked it would fire perfectly in semi and full, auto after new contacs and cut off lever.I have removed the gearbox ant tried to fire it on semi outside the body so the selector switch and plate is not the issue.
SHS 16:1 gears
SHS high torque motor.
one of biz 96's AB mosfets
G&G trigger contacs
All in D'boys reinforced shell.

the previous shell was A&K i think ive tried 3 diffrent used cut off levers with no sucesss.
Is there anything else im missing?

Have you checked that the sector gear fully contacts with the cut off lever when it is tensioned by the spring?

.22 Lover · 08-03-2014 9:23pm

the cut off lever does move slightly when it cycles but no enouf by the look of it to engage the contact.

matty1994 · 08-03-2014 9:25pm

.22 Lover wrote: »

the cut off lever does move slightly when it cycles but no enouf by the look of it to engage the contact.

Have you checked the shimming? The cut off lever itself and the little bump at the bottom of the sector gear?

.22 Lover · 08-03-2014 9:39pm

The shimming seems ok ive done it myself and all the gears set in place but ill try re shim the sector tomorrow and see if there is any sucess.
I have tried 3 diffrent cut off levers all with fairly high ramps on them but ill get another on just to make sure.
And what do you mean by the bump on bottom of the the sector gear?

matty1994 · 08-03-2014 9:41pm

.22 Lover wrote: »

The shimming seems ok ive done it myself and all the gears set in place but ill try re shim the sector tomorrow and see if there is any sucess.
I have tried 3 diffrent cut off levers all with fairly high ramps on them but ill get another on just to make sure.
And what do yuo mean by the bump on bottom of the the sector gear?

Try the gear with no shims and see how that works ? And the bump at the bottom of tge sector gear that looks like a cam, check to see if its not worn

.22 Lover · 08-03-2014 9:47pm

Ahh ok i know what you mean.the cam part of the sector is not very worn at all the SHS gears havent seen all that much use.It just seems to be this new dboys shell thats giving me trouble.
Ill try the gear with shims tomorrow ant tell you of the results.
I cant do it now beacause next doors child would not be happy with alot of aeg shooting.
Thanks for the help matty.

matty1994 · 08-03-2014 9:50pm

.22 Lover wrote: »

Ahh ok i know what you mean.the cam part of the sector is not very worn at all the SHS gears havent seen all that much use.It just seems to be this new dboys shell thats giving me trouble.
Ill try the gear with shims tomorrow ant tell you of the results.
I cant do it now beacause next doors child would not be happy with alot of aeg shooting.
Thanks for the help matty.

Ah ok, just i had troubles before with mine and it was due to the shims lifting the cam over the cut off lever giving me only full auto, just had to remove the shims and gradually add thin ones to make it work fine, let me know how it goes anyway:)

T4RGET · 09-03-2014 11:02am

what exactly happens when you try to fire it in semi? nothing or does the motor try to turn, is there a grinding noise?

Have you made sure you put the little spring back into the selector plate? It sits on the outs of the GB. Make sure you put it back when you were changing gearboxes.

Other than that give me some more info as to what happens, or doesn't when you pull the trigger on semi?

.22 Lover · 09-03-2014 5:43pm

it fires perfectly fine only in full auto.when i put the selector plate to semi is still fires in full auto.and i havent put the gearbox back in the shell yet so it can not be any problem to do with the selector switch.yes the spring still in the gearbox its not the spring.

T4RGET · 09-03-2014 6:38pm

We'll it's definitely a probably with the selector plate or cut off lever.. Sounds lie the new receiver doesn't engage the selector plate properly though

.22 Lover · 09-03-2014 6:47pm

So what would be the souloution to that?

T4RGET · 09-03-2014 7:53pm

.22 Lover wrote: »

So what would be the souloution to that?

well my guess is the new receiver you have is slightly off spec and isn't actually engaging the selector plate properly when you flick the selector switch to semi. So the best thing to do is try another receiver, like if you have a spare one lying around or a mates and see if that makes a difference. Then you could also try do some measurements to see if the tab on the inside of the selector switch is actually pushing the plate far enough to engage semi inside the gearbox.

Does any of that makes sense?

.22 Lover · 10-03-2014 3:45am

It all makes sense to me but my problem is that i dont have a backup gearbox shell the one im using is the backup! Looks like im gonna have to get another shell and im very sure that will fix my problem.

T4RGET · 10-03-2014 10:44am

.22 Lover wrote: »

It all makes sense to me but my problem is that i dont have a backup gearbox shell the one im using is the backup! Looks like im gonna have to get another shell and im very sure that will fix my problem.

well you've said that the previous one was an A&K shell and this one is a DB one, but i can't imagine them being so different so it is odd.. have you tried connecting the pistol grip and inserting the motor and manually engaging semi by moving the selector plate yourself?

.22 Lover · 10-03-2014 5:25pm

yes that is how i have found the problem.
The dboys shell does seem to have thicker walls resulting in the spring having to bend in abit to engage the cut off lever,But it still does engage it and push the lever into what should be semi position.
Also another very annoying problem is that beacause of the slightly diffrent design of the shell and the 2 extra trigger wires from the mosfet every time i remove the motor it gets stuck and the only way to remove it is to pull i out with a pyliers the result is it tears a small chunk of the wire cover from the motor wire every single time. :mad:

T4RGET · 10-03-2014 8:33pm

.22 Lover wrote: »

yes that is how i have found the problem.
The dboys shell does seem to have thicker walls resulting in the spring having to bend in abit to engage the cut off lever,But it still does engage it and push the lever into what should be semi position.
Also another very annoying problem is that beacause of the slightly diffrent design of the shell and the 2 extra trigger wires from the mosfet every time i remove the motor it gets stuck and the only way to remove it is to pull i out with a pyliers the result is it tears a small chunk of the wire cover from the motor wire every single time. :mad:

then i think it's just a simple compatibility issue im afraid.

CpcRc · 10-03-2014 10:03pm

Just had a quick read over this so didn't get all details but is it that the gearbox won't fire in semi auto at all even outside the gearbox, if so then this might help otherwise skip it.

Not sure if this was mentioned before, but some trigger boxes have slightly different notches that engage with the cut off lever. It might be related to the gearbox being slightly different as the example I'll give is with a dboys/jg gearbox I use.

I had to slightly take a little bit off the notch that engages with the cutoff lever on the upper part of the trigger contacts so that it could properly pull back and release the sliding part which engages with the contacts. I have to switch the aeg back into safe after full auto to make sure the cutoff lever is set for semi auto. It's not ideal but the aeg fires quite reliably so long as I operate it right. To test if it was working alright I placed the trigger box, gears and cut off lever in the shell and put the two halves together. I moved the gears with my finger and checked to see if the cut off level disconnected the trigger contacts every cycle with the cutoff lever in the semi auto position.

Just thought I'd add something I experienced in the past that stopped me from being able to semi auto. I think I had another old trigger that worked without modding but it had some damage so I couldn't use it and had to mod a new one.

.22 Lover · 11-03-2014 4:53am

I dont quiet understand what you did.
Could you explain this to me in abit more detail.

CpcRc · 11-03-2014 11:59am

As the gears rotate they eventually push down on one side of the cut off lever. This raises the longer arm side of the lever. You will notice this has a bit of extra material on the end.

The trigger contacts have two separate pieces, the part with the plates that stays fixed in the gearbox and another part which slides along to connect the contact plates and is pushed by the trigger when you pull it. If you take out this part you will notice that there is a bit of extra material on the side that faces down towards the cutoff lever.

These two notches connect with each other and as the cutoff lever pushes up on the part from the trigger contacts it eventually causes it to "snap" backwards and disconnects the trigger contacts. This is because the cutoff lever pushes the sliding part up so it is no longer being pushed forward by the trigger and the return spring it has pulls it backwards. This is how the cutoff lever stops the gearbox from firing, otherwise it would keep going until you release the trigger and the sliding part returns backwards normally.

The issue I am talking about is when the cutoff lever cannot properly push up on the sliding part of the trigger contacts enough to cause it to raise above the trigger that's pushing it forward and snap back until the trigger if released and slides behind it again.

If you look at the two notches you will see that they both have pointy sides and these are the two parts that rub off one another. The slope helps the cutoff lever push up and once it clears it helps it to return downward again.

To test this you assemble the gearbox like you would to test shimming without the cylinder, piston, spring, etc. so that you can use your finger to rotate the gears through the slots where the cylinder goes. But this time you make sure the cutoff lever and trigger parts are installed

As you spin the gears you should notice that the cutoff lever moves up and down with each cycle. Now hold the trigger down and rotate the gears eventually you should feel a point where the cutoff lever will be pushing up on the trigger block. The gears will be a little bit harder to turn. Eventually the cutoff lever should push up enough and the trigger block will snap backwards even though you have the trigger pressed. If the trigger block stays forward then the cutoff lever isn't able to properly disengage the trigger block because it can't push up enough.

In my case the plastic notch on the sliding part from the trigger was too far forward so I needed to remove some material so that the notch was farther back and the cut off lever could push it up properly on each cycle. You have to be careful because if you remove too much then the cutoff lever will never work as there won't be a notch there for it to push up on or not enough notch left for it to push up enough.

I hope that answers enough.

Edit: writing long messages on a phone is a pain

.22 Lover · 12-03-2014 3:30am

Thank you for taking the time to wirght all the on a phone no less.
I understood that perfectly.ill give it a try and see what happns.

.22 Lover · 13-03-2014 7:58pm

I have found a soultion in the form of my first gearbox shell i screwed up with a drill managed to bring it back to life and works fine now its also a dboys gearbox just not as chunky.
Thanks for all the help lads.

M4 not firing on semi.

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