repetitive piston break with not so powerful AEG - what's wrong?

[Jimski]

Hello all !

I broke a polycarbonate piston in a TM Aug I just upgraded last week.
the upgrade was light, just a high speed motor EG1000 and an m120 spring.
However the piston broke after a few mags, even though the AEG had been performing amazingly well just before.

(the shimming job, greasing, oiling and soldering and all having been done with great love and care )

Furthermore, the one and single previous failure of this AEG being another piston break (with the stock motor), I was wondering: what the hell could be wrong ?

Will I solve anything with an aluminium piston ?

Thanks!
cheerz


Jimski

[CDN_Stalker]

Take it apart and try sliding the piston (ok, the next one definitely) in the grooves on the inside of the mechbox. If it's like what I experienced with a Guarder FTK in a V2 Hurricane reinforced mechbox, the piston's side grooves were too tight on the mechbox rails. What happened after I upgraded it but before I found the problem was (go figure, I fired off 6-7 locaps through the M4, shot great, Shagg got it back, it cycled twice then siezed), so once I discovered this I used a sharp but small chisel and shaved plastic off the insides of the groove til both sides slide smoothly.

I know that isn't your problem, but it is a though, because if the piston decides to seize yet the gears keep turning, you can royally fuck a piston pretty easily (hey, I've seen two polycarb pistons break in the past 4 months due to the hop up rubber going kaput. Different guns too, although same owner! :roll: )

[trevor]

I was taking out pistons with my M4 with a M120 spring. I bought a deepfire titanium piston and all the problems have went away. The piston is made out of a fiber so the gearbox does not take the pounding you’d get if you used an aluminum (and no loss in rpm) but the gears are all metal so you get 0 wear. They are more money but are worth it in the end. A guy in our club has been using his in a heavily upgraded gun for a long time and it still looks like new.

[Jimski]

Thanks a lot guys.
I will think about that...

[Greylocks]

The M120 is a stiffer spring than you think, and has been known to cause problems.
Pick something a bit milder from another company if you continue having problems.

[Skruface]

Check out MadMax's "ROFinator" thread - he was stripping pistons in an M249 and realized that the piston head he was using was +/-1mm thinner than the stock one, and was causing his teeth to be out of alignment with the gears at the "full stop" position of the piston, stripping the piston. You may have the same issue....

[ringsted]

you shoud be just fine with an ordinary TM piston.

remove the second tooth on the piston to make sure it is grabbed properly by the sector gear. you mig also have to shim the piston a little bit back, to make the engagement perfect. just put som kind og metal washer between the piston and piston head, and use a longer screw.

running a low ROF under 23 per second should give you well over 40000 rounds before the piston breaks.

keep the barrel clean, most of the times a piston break because a BB gets partially stuck.

[Jimski]

ok,I will make sure 'tis done.

thx

[Kokanee]

To this day, I still run stock TM pistons/head in most of my aeg's. They are still fairly resistant to wear, and if the teeth on the piston wear down after a season of playing, it's like $8 to replace instead of the ransom that guarder or systema will demand from you.

My M4 is running a prom 110 and a stock tm piston assembly, no problems at all - but it's shimmed to a T and i don't have any resistance problems.

One thing I have seen in some mechboxes from a variety of manufacturers is that sometimes you will see small voids or bumps in the surface of the mechbox where the piston slides back and forth. Despite the fact that they are usually small (less than .5mm), they can cause resistance issues or compound an already existing problem.

With my previously mentioned M4 (ICS), I went thru three pistons in three games (stock ICS, Guarder and Systema area 1000), before I finally completely degreased my upper mechbox and noticed the voids/bumps. Starting with a 600 grit sandpaper and working my way down to 2000 grit, the insides of my mechbox are now mirror smooth where the piston slides, and lo and behold, no more problems with pistons breaking.

So it's a long shot, as it's not particularly common, but try wiping the lube off your mechbox and checking for voids/bumps.

gotta agree with Kokanee there. Of all the fancy and expensive after market pistons, none take a beating like the stock TM piston.

[MadMax]

Originally Posted by Skruface

Check out MadMax's "ROFinator" thread - he was stripping pistons in an M249 and realized that the piston head he was using was +/-1mm thinner than the stock one, and was causing his teeth to be out of alignment with the gears at the "full stop" position of the piston, stripping the piston. You may have the same issue....

I don't think that should be the problem as I'm guessing a TM piston head is being used and not the short CA one.

A little more detail would be useful though. How is the piston failing? Is the big first tooth snapping off? Are the first three teeth wearing down?

[fidget]

I've run a DeepFire Single Ti tooth piston, Systema M120, Ca BoreupKit, with Silent Piston head. I've never had a problem what-so-ever. I have noticed some wear on the piston, but its easily gone through.. 40k rounds..

[CDN_Stalker]

Originally Posted by Skruface

Check out MadMax's "ROFinator" thread - he was stripping pistons in an M249 and realized that the piston head he was using was +/-1mm thinner than the stock one, and was causing his teeth to be out of alignment with the gears at the "full stop" position of the piston, stripping the piston. You may have the same issue....

I found the same thing, except it was the piston body that was about 1mm shorter than the piston that worked fine. It would sit slightly forward in the cylinder, the sector gear's rear tooth (the big one) wouldn't engage with the piston teeth properly, ended up shaving a curved notch in that large big tooth at the end. For the heck of it, since it seemed that piston could still work, I put in a washer or two between the head and body, which would align the piston with the sector gear, but the damage was too much for it to work after that.

After a couple stripped pistons, same place, same cutout from the sector gear, the owner said to hell with it and we kept the stock TM piston in there and no problems since.

I agree with Kokanee and Droc as well, TM pistons have never caused any problems for me. Heh, I remember Kokanee's M4 going down one of those days, during respawn he showed me the broken piston in his mechbox. He relied on his 1911 spring the rest of the day, made the mistake of trying to sneak up on me from the side while I was "pot shotting" guys in the base.