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Part #37 Cylinder Base Plug Problems


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#1 Jatodude

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Posted 28 May 2013 - 01:06 PM

I've had my LM4 for about a year, and the majority of the time full auto hasn't functioned correctly. I first replaced the piston o-ring in hopes of eliminating the dropping bb's, and more recently replaced the hop-up bucking. Both of these things improved the performance, especially replacing the swollen and torn bucking. I also bought the original piston o-ring for the LM4 to try. My piston return spring broke, and in my efforts to make my gun operational I just wrapped the spring around the pin again. It actually worked very well, better than I'd ever seen since the dropping started. But there was still compression loss on full auto.
I found that since the spring had become stretched out and weaker, the piston maintained its position around in the hop-up for a longer time, helping the cause. Full auto was almost usable. I disassembled the piston again, and put the brand new KWA o-ring on the piston, and clipped a few rings of the piston return spring because the base plug was actually hanging out of the piston a bit. The piston didn't completely return to the bolt. This yielded poor results on full auto.
What I found eventually, is that after firing full auto, the piston would become stuck inside the bolt. It was extremely difficult to pull it out by sticking my finger in the ejection port and just pulling on it. Firing on semi auto a few times would fix the problem though. So I went full auto to let it stick, then took the piston out of the bolt immediately. I found that the cylinder base plug (part #37) was actually stuck inside of the piston, causing premature removal of the nozzle from the hop-up chamber and making the bb's roll. Has anyone experienced something similar? What could be causing it to stick? A swelled o-ring perhaps? Any advice at all would be greatly appreciated. No mods whatsoever have been made, other than replacing the piston o-ring with the HNBR, and replacing a swollen bucking due to over-lubrication (trying to solve full auto issue).

#2 netpoc

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Posted 28 May 2013 - 05:38 PM

Clean the nozzle, the end of the bolt, and the chamber area outside of the hop up. Make sure there is NO grease or any other foreign material in that area. Truthfully I have found that the only thing that needs lube is the piston o-ring, everything else can and should be wiped clean. Try it and report back. ;)

#3 BoobieM4H

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Posted 28 May 2013 - 06:45 PM

The hole at the end of the nozzle that the plug goes into I've made slightly bigger so the plug doesn't wedge itself anymore. I used a dremel with a coned shaped grinding attachment.  This happened to a friend of mine during the winter. Everything would get cold and the plug would just wedge itself in and get stuck. Don't remove to much material. Id say just scratch the surface with the dremel bit

( o Y o )



#4 JonathanNCP

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Posted 31 May 2013 - 10:25 AM

pictures?

#5 jakattack1987

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Posted 31 May 2013 - 05:06 PM

mine gets jammed all the time, i never thought of it causing problems in full auto, my lm4 has always had problems in full auto as well. i will have to look into this thanks for the heads up, i just figured it was the hop up because i know the compression is good.

#6 BoobieM4H

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Posted 04 June 2013 - 11:00 PM

 JonathanNCP, on 31 May 2013 - 10:25 AM, said:

pictures?

heres a short vid.

https://www.youtube....h?v=-zZpSdcXdHg




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