KWA Problems.

Brand new KWA SR12 not a week old.

What the hell could have caused that...?

Any suggestions for a new piston to replace it?

How many times have you fired it? What strength spring?

superchrisguy wrote:How many times have you fired it? What strength spring?

Maybe 600 rounds. All the internals are stock the spring should be 120. Brand new gun.

Well then there goes my theory. Maybe a lemon?

Harsh pick up tooth force, terribly shimmed gears, bad AoE. Sadly KWA's have odd gearbox specs so you are going to need either a KWA piston or a Prometheus piston. To further prevent this problem, adjust your AoE, lighten the piston assembly and replace the aluminum piston head with a ported one. Make sure your gears are spinning smoothly without any gear whine.

logical wrote:Harsh pick up tooth force, terribly shimmed gears, bad AoE. Sadly KWA's have odd gearbox specs so you are going to need either a KWA piston or a Prometheus piston. To further prevent this problem, adjust your AoE, lighten the piston assembly and replace the aluminum piston head with a ported one. Make sure your gears are spinning smoothly without any gear whine.

OMG! KWA uses shimless gears and poorly shimmed gears has nothing to do with a piston breaking! No shims are needed in a KWA! I also havent seen any problems with other name brand pistons in a KWA, so your wrong there. Ive used.... Deepfire, SHS, AIM, modify quantum, element, modify ultra, etc. My guess is a lemon... KWA would have warrantied it also. I ran my stock piston with a M170, magnum motor and 50c 5000 mah 11.1 lipo (23+ RPS and 550+ fps) shooting semi AND full auto and it lasted about 25k rounds which isn't bad for the amount of stress I put it through.

really bad AOE (angle of engagement). the sector gear pushed up on the pickup tooth and it finally gave way. normally it's not a problem when using slow 8.6v batteries, but sometimes when going full auto on higher amp batteries, it will cause more stress. that can be fixed by either putting 2 nylon flat washers between the piston and piston head (longer screw may be needed) or a rubber washer glued to the cylinder head (my preference for higher spring rates). the 2nd tooth on the new piston will need to be shaved and possibly the third tooth may need to be trimmed. i recommend an SHS 14 teeth rack since it already has the 2nd tooth removed.



next time i work on a cqb AEG, i'll make a video using the flat washer between the piston/piston head.
the rubber washer on cylinder head has worked great protecting v2 gearboxes without using sorbo.

Thanks everyone. Good stuff to go off. Thx for the video too Alex, cleared up my questions about the AOE setting.

Rhino wrote:

logical wrote:Harsh pick up tooth force, terribly shimmed gears, bad AoE. Sadly KWA's have odd gearbox specs so you are going to need either a KWA piston or a Prometheus piston. To further prevent this problem, adjust your AoE, lighten the piston assembly and replace the aluminum piston head with a ported one. Make sure your gears are spinning smoothly without any gear whine.

OMG! KWA uses shimless gears and poorly shimmed gears has nothing to do with a piston breaking! No shims are needed in a KWA! I also havent seen any problems with other name brand pistons in a KWA, so your wrong there. Ive used.... Deepfire, SHS, AIM, modify quantum, element, modify ultra, etc. My guess is a lemon... KWA would have warrantied it also. I ran my stock piston with a M170, magnum motor and 50c 5000 mah 11.1 lipo (23+ RPS and 550+ fps) shooting semi AND full auto and it lasted about 25k rounds which isn't bad for the amount of stress I put it through.

Let's think about it, if you have gears that are improperly meshing, the sector gear can contact the piston off the center of the teeth, and with improper engagement (side to side, not AoE) the tooth will break off easily. With that said, YES gears can be the cause of piston stripping.

I have taken calipers to KWA's gearbox, and even called KWA to confirm this. The gearbox shell has bearing holes off distance to the piston which is the reason why KWA uses longer teeth on the sector and piston to increase the torque of the gun. This is why they are so darn slow on a 11.1v 3000 mah 30C compared to say JG or G&P. Even though the distance is minimal it was enough to cause the plastic teeth to wear down over time (very slowly, the meshing was just bad so the teeth wore down very little by little) I took the piston out before it got worn down more. However when I measured the teeth of the Prometheus piston the teeth were the longest, and the shape matched the teeth of KWA's gears. If you don't believe me ask anyone at KWA and they will tell you that they used the design of the Prometheus piston for theirs. I'll admit KWA makes great pistons, with proper reinforcements around the pick up tooth. This leads me to question why your pistons tooth broke, as it seems like something else would break first. I suggest you send it to KWA so you won't have to deal with any off spec part replacements.

i've seen a number of AOE cracks. that's one of them. you can tell by how the chunk cracked off. it was an upward force.

-a|ex wrote:i've seen a number of AOE cracks. that's one of them. you can tell by how the chunk cracked off. it was an upward force.

You're 100% right but KWA's have always come like that and lasted for thousands of rounds on other peoples guns. I'm thinking it's just a faulty piston.

Sorry if I'm grave digging posts but I registered just to say I had literally this exact same problem happen to me on Sunday. Same breaking point and pattern as shown in the image above... And while my gun is about a month or so old it has less that 10,000 rounds through it with no upgrades and a battery within spec. Not to mention the stock pistons are sold out everywhere. So if anyone has a good brand that won't require any modding and hopefully won't be destroyed again so quickly around the $40 range I would really appreciate it. -Regards

see my video on correcting AOE, i do that to AEG's whenever possible. some use nylon washers on the piston, but that requires a longer screw and doesn't help reduce gearbox stress (for heavier springs). if you are using stock springs, any piston with a ported polycarb head will work fine. sometimes, you may need to replace or stretch out the piston o-ring for a better seal.