interesting piston failure
 

this is an aluminium piston;

http://i225.photobucket.com/albums/d.../alupiston.jpg

anyone knows why it broke at the first tooth like that ?
the battery I used was 10.8V / 5000 mAh, the spring is under 350 fps.

does it mean that the piston breaks when the sector gear catches it ?
1.I suffered some misfeed the mag before the failure, but not on the mag during the failure, that was spitting BBs like there was no tomorrow.
2.When I took it apart there were two bbs jammed in the barrel.
3.BBs are Bastard tracers.
do you think a plastic piston will explode into a million pieces if I try it on this config ?
is that clearly jamming-related?
thx all

Barrel jammed and the piston took longer to finish it's cycle, and got struck by the gear? Just think of when you kick a soccer ball when it's coming toward you, it goes further as the impact is bigger than if it was stopped...

The piston broke because your gun jammed.
If you continue shooting on a jammed gun, it's a downright guarantee you'll break the piston.
It's absolutely retarded to make a piston out of cast aluminum, it has very little elastic give to it, and simply cracks and breaks when stressed. Polycarbonate however has much more elasticity and is much more resistant to the stresses a piston is exposed to.

So buy a polycarbonate piston and use a 9.6v battery

That's one of the most common piston failures. The next probably being a bunch of stripped teeth.

okay, thanks to you all :)

are bastard tracers prone to jamming?

I"ve never shot the bastards tracers, but it may not be the fault of your BBs. Can be the Mag, or the hopup has far too much downward force and keeps BB's from being expelled out the Barrel, or the hopup rubber is too hard preventing BB's from getting expelled.

If it's the hopup's "fault" you can test it by taking it out. Manually load a BB down the chamber. The bucking should hold the BB in place and a light push (IE almost no force) with a stick should send the BB down the barrel.

Most of the jam strips I've seen strip the piston somewhere in the middle, whereas a pickup tooth failure is associated with incorrect AoE. In a jam the piston can't reach the front of the cylinder because it is jammed, leading to the stripping of teeth in the middle. If the sector gear was able to repeatedly hammer on the pickup tooth at an odd and stressful angle until failure, then we at least know the piston was firing out BBs most of the time.

Your angle of engagement (AoE) may be insufficiently set to prevent catastrophic failure.

Amos made a very nice video about this on his YouTube channel. Go check it out, he explains it visually.

Basically, you want the first tooth of your sector gear to strike the pickup tooth on your piston flat-face-on-flat-face -- i.e. maximum contact surface area. The best way to accomplish this is to get a sorbo pad (airsoftparts has em) and stick to the rear of your cylinder head. This will move the strike position of your piston back enough that the two teeth can achieve this angle of contact. You'll then need to test the engagement out by hand and check if you need to remove any teeth from your piston to allow the sector to hit the pickup tooth before hitting anything else.

I wonder how Tokyo Marui would have changed their original design of the mechbox if Japan didn't have their sub-300fps safety regulations.

you can also remove the first regular sized tooth on the rack to help with AoE, easiest thing to start with in terms of adjusting AoE, if it needs more adjustment, then you can shim between piston and piston head, or you can sorbo the cylinder head... sorbo is good because it will absorb some of the shock at the front of the gearbox.

Also, if your piston is full aluminum, it probably weighs more than a polycarb or poly fiber piston, trying to change direction of movement on something with much more inertia can lead to what you have there.

They would have made it reinforced from the start and used better casting material than zinc alloyed lead lol

They weigh very close to the same amount, huge different in the materials is in elasticity. Polycarbonate absorbs shock, cast aluminum does not.

that would've been my second guess :p

faulty hop-up nub, from an upgrade hop-up unit.
I am reverting back to stock... my experience with upgrade hop units is that they mostly suck.

interesting, thanks!

Hey, by the way, if you know this information, I'd love to know what the identity of the broken piston is (brand/model). Any idea?

systema
check on UNcompany

Thanks, not looking to buy, looking to avoid :)

duhh