Gearbox lock, please help

box27

Just installed a new VFC version 2 and a g&p m120 motor in my m4 but every time o fire the gun the piston locks in the full reverse position. Any ideas as to what could be the problem?

Thanks,
C

DeBurca

Was the gearbox fully working before you fitted it to your M4 or have you done a bit of work on the box ??????

box27

Had to open it up to change the selector plate do it'd fit in the receiver but didn't I didn't change any of the internals around.

I can release it by tripping the anit reversal latch but as soon as I fire again it locks up.

DeBurca

Only thing that springs to mind (pardon the pun) is the spring were the bottom coil had pushed the end of the coil out over the lip of the spring guide and was catching on the inner bore of the spring stopping it from moving all the way backwards
Much more likely to happen if the spring has been cut

box27

No it's not that, thanks for the help anyway.

DeBurca

If you are sure that the box is OK then it must be the motor and/or its wiring

Do you have a different motor to run it with as a means of eliminating the motor, if it runs then its the motor if not then the problem is either the wiring or its within the gearbox

box27

I actually think the box is the problem I just can't figure out what part. The motor runs fine when isolated from the gun.

sharpy2010

The motor will run fine when not in the gearbox as there is no load on it so it still maybe the motor. I would take deburca's advice and try a different motor to eliminate that. When you took apart the gearbox did all the shims go back as they were as it may be putting extra load/friction that the motor can't handle.

box27

Ok I'll try a new motor, thanks, but no all the shims appear to be ok.

DeBurca

As your gearbox is a VFC does it still have the Original self shimming gears ??????

box27

Sure does, along with 2 or 3 shims here and there. The gears aren't stiff though, They spin freely when placed in the closed gearbox by themselves.

DeBurca

Then all should be good, have you tried removing the spring and bolting the box back together and seeing if you can turn all the gears and check that the pistons can go all the way back and forward again freely

Southern Dandy

Is the motor seated correctly in the pistol grip?. With the motor to high you will hear a grinding noise, if it is even closer you will get a very slight humm and the gearbox won't turn.

Strip the gearbox down again once you have eliminated that it is not the motor, provided your than comfortable to do so and scrutinize every part!.

glicster

dont suppose the AOE mod has been done and the second or third teeth not filed down enough that the spur is catching the piston premeturely? just something else to look at

box27

There was a failure in the wiring this evening, is it possible that the wiring could have been faulty and that caused the problem?

Southern Dandy

box27 wrote: »

There was a failure in the wiring this evening, is it possible that the wiring could have been faulty and that caused the problem?

Yup a direct short, or a loose connection will defo do it there won't be a peep out of the gearbox. Is the fuse blown? That is if you have one.

box27

Well the gearbox did cycle just not fully, it was one of the connectors that attaches the wiring to the terminals on the motor.

Southern Dandy

box27 wrote: »

Well the gearbox did cycle just not fully, it was one of the connectors that attaches the wiring to the terminals on the motor.

Yeah its an intermitent electrical fault, being an electrician by trade i can assure you it does happen have seen it with motors that drive huge mechanical parts for example, airsoft gearboxes are the the same principle just on a much smaller scale.

And is the gearbox working ok now?

box27

Nice one, I can't test it yet unfortunately, have to wait for the new wiring assembly to be delivered

Southern Dandy

box27 wrote: »

Nice one, I can't test it yet unfortunately, have to wait for the new wiring assembly to be delivered

You could solder the cable directly onto the motor tab, I did this to my aeg for simple reason its a better connection but only balls is you have de-solder it when you do a bit of work to it.

box27

Ye I'll look into that to see if it is the the wiring that's the problem , can always just de slider it when the new wire harness arrived

Just a Plinker

Have you adjusted the motor adjust on the end of the pistol grip??

box27 wrote: »

Ye I'll look into that to see if it is the the wiring that's the problem , can always just de slider it when the new wire harness arrived

box27

Alright so this is now the situation, wiring has been cleared as a cause of the problem, the motor is too (works fin in another gearbox). Its almost as if the piston can't move back far enough to disengage itself from the sector gear. Any help? thanks

Inari

Do you have a bearing spring guide and bearing piston head? These two parts sometimes bind on each other preventing the gearbox from completing its cycle. Remove one (replacing it with a non-bearing part) and see how you fare. I would recommend keeping the bearings on the spring guide, as there's less weight on the piston allowing for marginally faster ROF.

Also check your shimming. If the motor's pinion gear is too tight against the bevel (under load) then it will be unable to turn. With the piston all the way to the rear the motor is under the most strain. Re-shim your gearbox to the pinion gear and re-test.

If the problem still persists have a look at your bevel gear, as it may be mis-cast...subtle deformities can cause infuriating problems.