CA M249 mechbox gear issue
 

Me and a friend were testing his M249 after fixing a short, we dry fired 10 - 12 rounds and heard a loud grind noise, after we opened it back up and removed the mechbox to open that up as well we found that the piston had 5 of its teeth ground off and torque up sector gear was also missing 2 teeth and the staft that the gear rotates on was snaped off.

Does any know why this happend and where we can find a higher quality replacment part (this will be the 3rd piston to be changed) ?

What's the main spring power and are all other part's stock. did a gun doc do the work on your gun like the shiming. did you use the right grease for the Cylinder. post up as much INFO as you can on your gun to help us out.

As far as I know all the parts are stock with the exception of the piston. I'm not sure what make or model it was (some sort of aluminum). Everything was greased and sliding nice before we test fired.

it could have happened for many reasons. if it was outside, the piston/gears could have become cold and thus brittle. Etc etc. Just replace the gears with known brands such as Prometheus, Guarder, Systema, or Modify (i have heard a lot of good from them despite the fact that they are new to the market). and get a new piston. I recommend Prometheus, Guarder and again Modify. I haven't heard much good from Systema pistons.

Best thing is to take it to your local gun doc. Most the time peep's think they know how to fix gun's but they over look thing's.

What spring (i.e. stock CA, M100, M110, etc...), what battery (i.e. 8.4v large/mini, 9.6v large/mini), what motor is in there?

What's likely is that the piston didn't get picked up by the sector gear properly...the piston has to be all the way forward so that its rear-ward most tooth get's properly picked up by the first tooth on the sector gear.

If the piston hasn't gotten all the way forward by the time the sector gear comes around again, the sector gear tooth with hit the 2nd most rearward tooth of the piston (and the 3rd and maybe the 4th)....mangling it, chipping it or just putting a lot of wear on it. That wear gets worse and worse until there's no good bearing surface left.

All the bits of plastic that come off the piston go somewhere...and it only takes a bit inbetween gear teeth to jam them...putting stress on things, which then mangles other things.

You really should replace all the gears at once....since worn gears don't fit nicely with new ones and different manufacturers have different engagement angles and tooth counts.

For pistons...I'd just put a Modify polycarbonate in there...but I have no idea what FPS limits you guys are playing at.

It's got the stock CA spring and motor and we were using an 8.4v 1700mAh battery

That's Devan's gun? That's an ICS piston, the stock yellow one didn't last even a few hundred rounds from what I remember, but that was years ago.

Looks like the sector gear shaft actually broke. Best replace it as well as the piston.

yeah mac its mine hahah,

Early CA M249 and maybe latter ones would destroy the pistons if too much hop up wsa set (no fucking idea why, it's CA after all!) and even tweaking it for use with 0.25g would set the destruction a going. Really bad design work on the early ones (I have one on my bench that was among the first in Canada) but it seems that even when a good piston and parts are in, the gun still eats pistons like crazy. Just testing this one while doing different wiring configurations causes chewed piston teeth, never mind actually GAMING it! This one has gone through a half dozen pistons in the past three years, and hasn't even been gamed much.

how the hell did you know that was devan's gun :P

and it did indeed snap the one side of the shaft off