breaking pistons in the classic army m15

[wohh]

I decided that I would upgrade my m15 after the first gears ate themselves. So I ordered the M130 spring, a Poly-carbonate piston, the super torque up gear set, and a classic army M16 bore up kit. I had some troubles getting it together... got a little excited taking it a part, but once I got it back together everything in place (followed multiple online guides)It fired about 2 bb's before I could hear the motor spinning. When I opened the gun the last two teeth on the piston were chipped off along with a small portion of the piston itself. I decided to see if it was the spring so I put my old piston back in and my old spring. Got it re-assembled and then tested fired it dry. The piston fired forwards once then got stuck pushed back against the very back of the gear box. After taking it apart again i realized that the gear connected to the piston had about 5 more teeth then the original gear. So, I pulled this the gear connected directly to the piston out and put in the old gear. Tested it for a couple shots. Worked beautifully ... untill the last two teeth of my original piston got ripped off too... I have 1 more stock piston left (got from a friends gun) and I don't want to use it until I figure out what is wrong.

Any ideas?

[djbordie]

shit sorry, i read your post wrong...

im guessing you cleaned out the gearbox well after the first incident?
any bits of plastic or metal could get in there and cause the problem again.

as for blowing the new piston, geez, it could be many a things.

I upgraded everything else in my CA, except for the piston, it blew and took a couple of gears with it the first time i gamed it. I then put in a set of Modify gears, with a polyC piston, sure enough, those gears died as well...i couldnt figure it out, but got it running again with mixed gears (luckily).

As for why this is happening, its a tough one...its gonna be alot of testing for you.

You really need to ensure you shimming is PERFECT, if anything is misaligned, your gears will slip and strip.

[Skruface]

Do you have a bearing on both the spring guide AND the piston head?

It could be that the spring, when fully compressed and in combination with bearings at both ends, is too long and is causing the piston to bottom out before it returns fully to the rear - as the gears keep pushing, the piston can't go any farther back, so the last 2 teeth tear off.

Compare the length of your new spring to the stock spring in a fully compressed state (if you can): put each one in a vice, slowly and carefully crank it closed until fully compressed, and measure the length of each one. Since I do some gun doc work, I built a crappy tool to help with this:



If the M130 is longer than the stock spring, I'd almost guarantee this is the root of your piston problem.

An easy fix is to use a non-bearing piston head; you only need bearings at one end, anyway. The other is to either buy a shorter spring, or clip one or two coils off your existing spring (although this will cost you some FPS).

[wohh]

I'll check it all out and make sure, I put everything back to stock with no upgrades for the time being since i had a game earlier, and had no problems with it, so I'll try to see what i can do with it tomorrow if i get a chance.