Piston Head Exploded

[Stinger]

I was test-firing my custom M4 when I suddenly lost all compression. It sounded fine, but I found shards of POM inside my inner barrel and they flew out of my air nozzle when I shot it with the upper receiver off.
I took it apart and, well, the Lonex POM piston head was completely shattered and looked like this:



What do you guys recommend as a replacement?
Also, is this a sign of anything bad? The gun has had about 50,000 rounds through it. M120 spring on an 11.1v 20C LiPo shooting 399 +/- 0.5 FPS around 22 RPS.
There was no sorbo pad, and the AoE was instead corrected from the factory by making the piston head longer. I plan on putting in a sorbo.
Also, I think the shards of POM may have clogged up the air nozzle and caused some pre-engagement, as the third last tooth (second-to-last being nonexistent) has been chipped. I'm thinking about getting an SHS Blue Piston and keeping it around until the current Lonex Extreme Toughness Piston inevitably fails.

EDIT: Before anyone says anything, the auto-shim on the spur gear is temporary until I get more shims so I can actually do it right. 

[ctres]

I'm not sure what to say other than that I once dropped a modify piston head (POM IIRC) from my workbench onto the cement floor and it broke similar to that except only along one edge. I always use sorbo but this doesn't seem like something that should happen regardless. As far as replacements most brands should work. Lots of people just use the cream colored ones from stock guns with the bearings removed. Otherwise if I were looking for one I'd probably go for lonex or something from shs.

[inj]

SO the AOE was not corrected when this happened, correct? Or was it the factory piston head? how was the padding on the cylinder head? What cylinder head was it?

As for replacements, I've been using ZCI nylons forever. They've not yet failed me and get great seal.

As for the Piston chip, It should work fine. However if you're ordering a new piston head, you may as well order a piston as well and put them in at the same time. Unless money's an issue, there's no point in waiting for the lonex to fail if you're ordering and replacing parts anyways.

[Stinger]

The AoE was corrected perfectly. It was the factory piston head. There was very little padding on the cylinder head, just like an O-ring like piece of rubber on it. It was an SHS Cylinder Head.

So is it bad to use thrust bearings in piston heads?

[ctres]

There is nothing inherently wrong with bearings in the piston head but the general concensus is that as long as you have bearings on the spring guide then the ones on the piston head are redundant and simply adding weight. Most techs try to minimize and the ammount of moving mass so it makes sense to remove them. This reduces fatigue on the gearbox shell and helps to minimize the chances of pre engagement.

[Stinger]

I don't have a ball-bearing spring guide.

[ctres]

It would be preferable to use a bearing spring guide and non bearing piston head IMO but you shouldn't have issues vice versa unless your setup is very demanding.

[Stinger]

Alright
So how exactly should I go about correcting my AoE with sorbothane?

[Snarf]

Well, not to be the guy who just links to the "Let me Google that for you" thing, but it's pretty easy to find a decent how-to video on youtube for that.

It's pretty self explanatory once you open it up. You just want the sector gear to mesh with the piston at the vertical position. You'll have to grind off some piston teeth too. Here's a picture that kind of explains it: i1201.photobucket.com/albums/bb351/philsaudio/kwa-g36-AOE25inchsorbo2.jpg

I put padding on the cylinder head rather than the piston head because it keeps the piston weight down and it doesn't cover up the holes for the ported piston heads. Also, being the cheap skate that I am, I opt to use rubber washers instead of sorbo pads. You can easily get a 40 pack of rubber washers for the same price as 1 pre cut sorbo, no joke.

[Stinger]

Well I actually already did all of that but thanks anyways.

[natethegreat32]

your shs cylinder head fits good into your "lonex" shell? i had to bevel the holes in mine to fit. Right now its a little iffy also.

[Stinger]

Sept 17, 2014 17:31:38 GMT -5 natethegreat32 said:

your shs cylinder head fits good into your "lonex" shell? i had to bevel the holes in mine to fit. Right now its a little iffy also.

Yeah, it was tight but it worked.

[airborn]

Parts do wear down. With it being the stock piston head at 50k+ rounds you can expect to start to see some parts fail. It's like a car in the sense that the older it is the more you have to replace and look after.

[natethegreat32]

The Stock ph on the fmg4 is not the actual lonex pom. Its made out of a cheaper plastic and doesnt have as many ports. There is also a hard plastic washer to try and correct the aoe behind the piston head. The pad on the cylinder head is extremely hard as well. The first time I felt it, I knew it was a matter of time before it broke.

[Stinger]

Sept 21, 2014 17:55:43 GMT -5 natethegreat32 said:

The Stock ph on the fmg4 is not the actual lonex pom. Its made out of a cheaper plastic and doesnt have as many ports. There is also a hard plastic washer to try and correct the aoe behind the piston head. The pad on the cylinder head is extremely hard as well. The first time I felt it, I knew it was a matter of time before it broke.

I was well aware of this, as I replaced it with a true Lonex POM and then corrected the AoE with sorbothane.
I think that, like you said, it was a lesser-quality plastic with no padding that was likely to fail after a decent amount of use.
I just wanted to make sure it didn't indicate any other possible issue.