Sig 556 problems - AGAIN.

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LazzurusMan

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So after I last worked on my sig everything ran fine. No issues, nothing. Then after three hours of play, she just stopped firing.

Ive opened up the gearbox anx found that my piston head had completely broken away from the piston, and the part the screw goes into had been chewed to hell.

Clearly a polymer piston was a bad choice for this build. Anybody got any advice on a full metal piston and head to use on a high rof build?

 
Are there any with all metal teeth? Id started ro strip the piston before the screw hole decided to shatter.

 
What piston did you kill, and what ROF/spring /stroke are you using?

 
Thank you. Looks like Ill be picking up a new piston and pom head on Thursday l.

Side note, anyone got any tips/thoughts on swiss cheesing? Is it really worth it?

 
You might loose a couple of grams with a moderate Swiss cheese job, but you loose 3 by ditching the bearing and replacing it with a nylon spacer. If you do Swiss cheese on a full metal rack piston then the rack needs to be epoxied in place. Don't interfere with the rails as it's easy to create points that can hang up and jam in the gearbox case. Don't compromise strength in the lower part of the piston either side of the rack.

Loctite is your friend... ;)

 
Just seen on another thread that your running ASG 30K stock gearing and 11.1v lipo. Don't bother Swiss cheesing the piston. You'll be getting around 22rps which is no where near PE. Neither do you need a full metal rack at that ROF on an M100 spring. If you're starting too strip the plastic teeth on the rack then something else is wrong.

 
I know I need to correct aoe when I instal the new piston...is there anything else that could be causing/cause damage to the teeth?

 
So the new parts are installed, and shes firing again. Solid 23 rps.

However, after using a rubber washer to adjust aoe, Ive lost 60fps, down to 270. 

Would adding a new spring bring me back up to 330? Is it even needed?

 
There is something off. If you use a washer to move the piston back, then the spring is more compressed so it should have raised the fps slightly.

 
Could it be my hop is set ro high? Had to adjust it when I last played, havent chnaged it back

 
If you had the hop adjusted up enough that you've lost 60fps then the only thing you'd be shooting at is low flying aircraft.

I take it you checked the air seal at all points of assembly? How thick was the answer you used?

 
The answer I used? And I checked air seal in the gearbox, it was fine. Will take the barrel out and check my bucking and the seal on the hop unit. Probably just needs some silicone lube.

 
Was just a cheap rubber washer thick enough to push the piston back to the right point. It wasnt large enough to cover the whole of the cylinder head, could that little bit of space be enough to reduce air going through the cylinder head and give a 60fps drop? And id saycit was about 5mill thick. Ill check tomorrow when I pick my gear up from our "team shed".

 
5mm is a bit thick, but not too bad. I don't correct more than 4mm. If you were undervolumed before then if there was a lot of space around the AOE washer then that might drop a few fps, but not 60. What length barrel and what cylinder type? And if the cylinder is ported, have you put it back in the right way around?

 
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