ICS M4 Gearbox / piston cycling 1 1/2 times * w/ sound recording
 

Instead of trying to explain this, here is a .mp3 of what it sounds like when the rifle cycles on single shot;

http://members.airsoftcanada.com/kok...ds/gearbox.mp3

There are 4 shots in semi total, with the 1st and 3rd shots completing a cycle and then some, the 2nd and 4th shots seem to decompress the spring.

I've triplechecked my shimming (just in case), motor height is great, and my anti reversal latch is installed correctly (more to the point, the edge is still plenty sharp, and the spring is strong).

This just started recently when I threw a prom ms110 inside. Still continuing after I've switched back to a lighter spring (don't know what it is, shoots about 330fps).

Rifle cycles well in full auto (however out of a 70 round mag, it will not eject a bb downrange on say, 4-5 shots throughout the burst), but the last shot behaves like semi, 1 1/2 cycles and then another press of the trigger releases tension.

I have never encountered this problem before, and the closest description I've been able to dig up here is an anti-reversal latch issue, but I made sure that mine is gtg.

Any ideas much appreciated.

Fixed

The problem was the locking lever on the front of the lower mechbox was installed the wrong way. I feel like a shmuck now. Anyway, I'm throwing this in the "solved" area, so if you have this problem, just pull your lower gearbox and reinstall that part. If you can't remember which way it goes, while the lower is open, fit the top mechbox against the bottom and you'll see there is only one way it can fit while the two halves are together.

*oops, this isnt the answer, see below for the fix

I was thinking about this before and was going to post my thoughts, and they sure weren't that. Are you certain that this was the problem, or when you opened up the lower to flip around this tab, did you inadvertantly correct the problem during reassembly? I suppose if your lower and upper were not lined up properly, I could see a feed issue, but cycling problems?

I was going to guess yaw bar and lube your hop-up!!

Just had a fellow today at a gun tech meet with the same problem - in a conventional gearbox. So I suppose it's not a locking lever issue.

i put a stronger spring in mine ( ics m16 ) and noticed that the semi auto firing was erratic. the weapon fires good on full auto just as yours does. the stronger spring doesnt allow the gears to complete a full cycle in semi and the tension release mechanism doesnt work until i run a f/a cycle. all this apparently is simply due to the stronger spring. my a3 made the same noise as your's does when i put metal bushings in the lower mechbox,, later i found out there was to much pressure on the lower reciever when reinstalled in the weapon due to shimming of the gears. the lower mech box needs to have some side to side play in the gears to compensate for the body squeezing the mechbox halves together when reinstalled. with your weapon split open do you have a small amount of side to side play in the lower gears? if not the entire assembly could be to tight,the gears should turn relatively smoothly taking into account some drag for the motor. if you cant turn the gears by hand and it feels like you could peel carrots with the thing,,im betting the mechbox is being squeezed tight by the body.

that sounds much more plausible, before i had the box shimmed so the gears spun freely but no side to side play... loosened the shimming up if i recall correctly, so that is prolly what fixed things.

good call!

im glad it worked out,,i wasnt sure if it was the solution needed,,,,it just happened to work for me.

I'm a gun tech here in the Peg, and I'm having this exact same issue with a clients ICS. However I out of curiosity sake tried it out without the upper on at all. The gears themselves seem to have this timing issue without haviing to pull back the piston and sping.

The gears that are in it are Prometheus from what I can tell. I was wondering if there are compatibility issues with gear sets? Could it be that the Cam on the ICS sector gear is at a different placement than on other gearsets?

I have honestly never had a gun where I have had soo much confusion. I have taken it apart alot, I left play with the gears in terms of shimming and this issue persists.

I can see that the Cut off lever is engaging at what appears to be an off timing. Will complete a full cycle, then a part cycle...etc; just for clarification its also doing this with the upper half connected.

Any Ideas?

Fixed somehow, I think it had to do with removal of shims as was advised above.

*EDIT* Client never told me what the problems were just handed me the gun and said it didnt work; I had the weird issue above fixed last night somehow, but then realized the safety didnt work. Fixed that but now the timing issue is back again.

Any further ideas guys?

from what im hearing there isn't a gearset compatibility issue with ics. the two weakest points of the ics design are the tappet plate and bad motors. if the motor gear looks good and the motor itself isnt causing you the problem,,,here's a link to mechbox.com. in this video it explains how to properly align and time the gear set. for what you need starts at around the 8 minute mark of the vid. hope it helps.

http://www.mechbox.com/site/mechbox/...ade-video.html

that really doesnt help at all unfortunately.

I have a ICS M-16A2, had this same weird semi auto cycle thing as well while I was running an 8.4volt battery, first in stock form then, shooting 390fps it was worse, I now run a 10.8 and it don't happen until the 10.8 starts to run down. (9.6 seems to work ok also?)

PS..are you guys getting lots of motor whine from your ICS, I have tried motor adjustment and putting in a System motor, still lots of whine, 8.4/9.6/10.8 bat makes no diff, gears free wheel nice no drag, must be inherent of their gear box (I know the anti-revers latch makes a ton of noise due to its design!)

i can't tell if my battary died or something wrong with the gun? i was test firing it and it just stoped, everytiem i pull the trigger it looks like the piston isn't pulling back at all? i opened it in half the gears spin fine the upper part doesn't move. any help here? i took out the battary and it was hot not to hot but it was warm?

Holy necropost

FIXED the battary wasn't dead but didn't have enuff power to pull the spring back :)