Lonex 8mm Enhanced Bearing Gearbox V2 M4/M16 = Piston scoring cylinder
 

Has anyone else had problems with Lonex gearboxes?
starting this build from scratch.
I was using Mad Bull PX Piston Full Teeth - ORANGE
with Modify Aluminum Bearing Piston Head
Modify S110 AEG Upgrade Spring and Modify Rotary Spring Guide V2
Running King arms normal torque gearset.

the teeth on the piston scratched the cylinder it went from 390FPS down to 200 fps. after a few shots
Swapped out cylinder and piston for an SHS Super Lightweight 14 Teeth Piston
it was shooting fine in semi with no significant fps loss until i switched it to full auto. and its now back down to 280FPS
Cant really see why its doing this. Just curious if anyone has had this happen.

kingarms gearset.

I've been told the tappet lug on these things is in the wrong spot so the tappet pulls away too soon from when the pistol releases so the air charge is still being delivered when the loading cycle starts. I'm not sure if you can fix it or not with a KA tappet, you'd have to mod it to fit the front end of the lonex gearbox.

easiest way to determine if the tappet timing is different is to compare another sector gear vs the kingarms and see where the tappet lug pin is in comparison to the sector teeth.

If it's different either a KA tappet might fix it, or just getting a SHS gearset will fix it.

Doesn't shs oem the KA gears?

As for the piston scoring the cylinder, you could grind a slight chamfer into the piston teeth to clearance it away from the cylinder

Can't confirm the oem or not, but just because company A oems for company B doesn't mean they will give the same product. Company B can order items to their own specifications.

Several other techs have told me they've had issues with KA gears and or KA tappets being oddball spec on several occasions,

Swapped the gears for some lonex ones i had. Problem solved.