M4 firing auto only at semi

[Jaxxin]

yes, i've checked the wear on the cut off lever. no wear

yes, i've checked if the screw is too tight. it isn't.

yes, i've tried putting the gearbox in to the body correctly. and i do put it in correctly.

yes, the fire selector switch is working.

yes, the selector plate spring is there and working.

yes, the selector plate slides without any problem.

yes, i've cleaned all the contacts, any excess grease, and anything that may mess it up.

for the life of me i can't figure it out. i even tried mimicking the gun firing just by using my fingers to push the trigger piece in and spin the gears with my hands, but i dont see how my gearbox is supposed to provide semi fire. nothing happens for the sector gear to stop turning. the cut off lever moves ever so slightly as the trigger piece (the one that bridges the connection) moves in and out but i dont see it ever moving enough to stop the sector gear. now there is one suspicion, and it's that my trigger piece is slightly deformed cuz it's melted a bit from my last gun. (dont ask... )

now can any of you guys help me by actually explaining to me how semi auto is supposed to work? if i know how it's supposed to work, then i can decide if the deformation of the trigger piece is the cause and get a new one, but I dont want it to still have the problem even after getting a new trigger piece. Or find out another way to fix this problem.

thanks in advance!

[sushicake]

Your Shims could be getting in the way of the cutoff lever. Same problem happened to me found out the shims were in the way.

[Jaxxin]

i see thanks for the help. I'll open the gun up again and try it sometime today. i would still love to hear other ideas

[Styrak]

Yup, could be too many shims on the cutoff lever side of the sector gear. Try only putting shims on the other side (if you need any).

Do you have any shims on the cutoff lever side of the sector gear?

[Amos]

Originally Posted by Styrak

Yup, could be too many shims on the cutoff lever side of the sector gear. Try only putting shims on the other side (if you need any).

Do you have any shims on the cutoff lever side of the sector gear?

... No Styrak you don't shim things that way.

There should be two different sizes of shims, if the shims are in fact your problem, use only the shims with the smaller outside diameter, some companies use a "Wider" shim to denote a certain thickness and I have seen instances where the cut-off lever has been messed with because of the the shims that were used were too wide.

It also could be a worn cut-off lever, have you tried cycling the sector gear by hand and seeing if it actually trips the cut-off lever?

[Jaxxin]

i havent had the time to take it apart again so i still dont know if it's the shims. but im doubting it a little cuz when i cycled the sector gear with my hand, with the tirgger piece being in the pushed in position, the gear did contact the cutoff lever, but the cutoff lever just kind of, gave way to it. i dont see it ever being able to stop it from spinning when the actualy motor is turning it at a high speed.