CA-25 munching pistons

[wKnight]

A friend of mine brought me a CA-25 that was only shooting about 270fps. Upon closer examination it had the usual poor air seals associated with the CA-25 and a damaged piston (2 damaged teeth behind the metal ones). So I dropped in a CA bore up kit to improve the air seals, replaced the gears with modify torque up gears, replaced a damaged piston and put in a stiffer spring (to get it back up around 400fps). Things seemed fine for a few games but then the gun completely stripped all the teeth off the piston. I went back into it, replaced the modify gears with CA gears and dropped in another piston. Once again the piston was stripped clean. If anyone could suggest what might be the issue here I would greatly appreciate it.

[hurbt]

How is your sector tooth to piston tooth alignment? Is the first sector tooth grabbing the piston at an angle? If not, then is the first sector tooth contacting the 2nd piston tooth?

Both of these are very common issues, and responsible for many a stripped piston.

Pictures are worth lots of words, so view this thread for more info: http://forums.airsoftmechanics.com/i...hp?topic=956.0

The solutions to both of these problems are simple. First, to get the 1st sector and piston teeth to engage at a better angle, you can either add some washers to the piston head, or add some sorbothane to the cylinder head. Either way you are pushing the piston back a little causing the sector gear teeth to engage with more contact area. I prefer to add padding to the cylinder head, which prolongs the life of the mechbox and does not slow down the piston (as adding weight in the form of washers, does). If you use sorbothane, you can purchase it at www.mcmaster.com for a whopping $4.47 US... i recommend the 70-OO hardness.

As is often the result of doing this, however, the first sector tooth will want to grab the 2nd piston tooth. The solution there is to grind down about 1/2 of the 2nd piston tooth with a dremel.

I did both of these things to my friend's G36, and its piston looks brand new after a year and 50,000 BBs through it on a PDI 190% spring (shooting around 400 FPS on full auto).

[wKnight]

this sort of thing was my first thought and its why i went back to classic army gears and piston as i assumed this would relieve any possible misalignment. all parts from nozzle to gears are now completely CA. It just doesn’t make sense to me that parts they make for their own gun wouldn’t align right. but, maybe I’m just giving them too much credit.

The other thing i should mention is this gun isn’t stripping just a few teeth off the end, its stripping the piston clean right up to the 3 metal teeth up front. If what your saying is the issue i cant see it being able to strip more than a handfull of teeth off the back end (correct me if i'm wrong).