Piston tooth keeps tearing off.

[Buds and Suds]

Well, I found out how the tooth is being broken off :banghead: after my 3rd piston. The tooth is being struck from the sector gear when it spins back. I saw a deep gear impression on the opposite side of the last (biggest) tooth. Its being torn off from the opposite direction. I didnt realize that it would have enough force to do that. So that being said, I also have a anti reversal gear that only has 2 teeth instead of 4 for the latch to catch. And I have been noticing a bit of excessive winding back after firing. Safe to say my problem is in my anti reversal? Which might also explain my double feeding issue I had when I put it all together.

[CDN_Stalker]

Ya, it could be, unwinding isn't good for the piston. Maybe just need a stronger spring on your latch to seat it properly. And putting a four lobe gear in is better than the two lobe one, I put a four lobe in one of my MP5s and it's a lot perkier now for trigger response in semi.

[m102404]

Originally Posted by Buds and Suds

Well, I found out how the tooth is being broken off :banghead: after my 3rd piston. The tooth is being struck from the sector gear when it spins back. I saw a deep gear impression on the opposite side of the last (biggest) tooth. Its being torn off from the opposite direction. I didnt realize that it would have enough force to do that. So that being said, I also have a anti reversal gear that only has 2 teeth instead of 4 for the latch to catch. And I have been noticing a bit of excessive winding back after firing. Safe to say my problem is in my anti reversal? Which might also explain my double feeding issue I had when I put it all together.

That's cool...I saw the same thing on another piston, but never thought anymore of it...I'll have to look at that again. All my bevel gears have 4 notches on them (just the way it turned out with the mess of parts)...I'll have to scrounge up a 2 notch gear and test. I did have a MOSFET unit that has active braking. The active braking kicks in as soon as the switch block is disconnected and is supposed to stop the piston (via the motor) as soon as possible after the power is cut. I'm not convinced it does any good on full auto, but for semi I definitely noticed that the piston was never "over-cycled" by a very fast setup. Never fully at rest, but just shy of it and very consistent.

But that would mean that the sector gear is un-winding almost a full half revolution back so that the "last" tooth on the sector gear is hitting the #1 tooth on the piston? Not sure about that, but something doesn't sound right.

Re. the piston lengths...
The measurements were taken quickly at the breakfast table with the pistons I had laying on the workbench. They were done carefully, but quickly, with a digital micrometer. The measurements were from the piston face to the outermost dimension of the piston body (the open end where the spring goes in). That said, the measurement does not take into account differences that may exist between where the position of the #1 tooth (by the open end of the piston) may be in relation to the face of the piston or where that tooth may be picked up by the sector gear. Each piston has it's own profile/bevel etc... around the open end of the piston. Also, different cylinder heads may or may not alter the end position of where the sector gear will interface with the piston.
So...it'd be false to say that a stock JG piston would or would not work as a straight replacement to a CA piston. It really depends on where the gear picks up the piston. Although, it is a quick way to check that you're in the ballpark to compare a piston that does work in that setup to a new combo when you're replacing things.

[Buds and Suds]

Alright after some trial and error using parts from my mp5 it has been narrowed down to the anti reversal spring. I closed my mechbox up and checked the movement without the spring or piston and the spring was not stiff enough on the anti reversal to catch everytime. And this is with a 2 prong gear. Some times I could wind it in reverse multiple revolutions without it catching. I took the anti rev spring from my mp5 and even holding it, it was alot stiffer. I put it in and tried the test again. It locked on every prong without fail. It even sounded different as I could hear the latch locking everytime on each gear as I rotated it.
So 1 weak spring cost me 3 pistons. Or so I believe cause I have no more to try it out. :banghead:
Anyways, my echo 1 mp5 antireversal gear has 4 prongs, while my CA m15 has 2. Both are version 2 mechboxes, are they interchangable? so I can put the mp5 one in my m15?

[m102404]

****EDIT****
Sorry, I reread your post above. For whatever reason, I thought you meant just switching the anitreversal latch/spring, not the bevel gears. Like Nova316 and CDN_Stalker say below, it's probably best to change out all three gears at once.

[Nova316]

i'd recommend u change the entire gearset tho not just the bevel gear

[CDN_Stalker]

Originally Posted by Nova316

i'd recommend u change the entire gearset tho not just the bevel gear

+1

PM Jugglez, he should be able to provide you with a new (aka. barely used) TM gearset for about $35-40. Is bettter than any aftermarket set such as Systema, Guarder and such, at least you won't have to de-burr the gear's teeth when you get them, and will work for a long time with any spring you put in your gun.