Help please grinding sound in full auto

[Sam-Bristol123]

Have a LCT ak74. Have installed a perun V3 hybrid and SHS 13.1 gears. Gears have Been shimmed and have been working perfectly but all of a sudden there was a grinding sound on both full auto and semi. Have since taken the gearbox apart and installed the old LCT 18.1, have tried a new motor, different battery and weaker spring and each time it fires perfectly flawless on semi auto but as soon as I fire in full auto I can hear a grinding sound. The gears are spinning but the piston isn't moving. So I'm thinking whether it ground (I think that's the correct word) down the teeth on the piston, but would've thought it would fire on semi. Any and all help would be appreciated. 

 

[strykerles]

Don't know much about LCT internals but I've worked on aa few V3 boxes and plastic teeth are the norm usually

there's a good chance as you say the teeth are worn down and can't quite grab the piston effectively in full auto

also it coud be that the gears are grabbing the piston too early and can't mesh very well depending on the spped of the motor and gears

I'd suggest trying a full steel rack and the slower gears then see how you get on then change to the faster gears if all is well

also what motor are you using?

 

[colinjallen]

A video of the gearbox cycling in semi and full auto would probably help us help you.

When you opened up the gearbox, did you take a look at the teeth on the piston?  Did they look worn or damaged?

 

[Adolf Hamster]

hmmm

if it was pme that ate the teeth on the piston then semi shouldn't be sounding too healthy either.

what sort of auto rof was it getting before it started playing up?

 

[ak2m4]

show us your piston, don't be shy