Legacy's Guide to Building a High Speed AEG

Discussion in 'Gun Building, Modifications & Repairs' started by LegacyAirsoft, Nov 21, 2013.

  1. LegacyAirsoft

    LegacyAirsoft You can say I tech a little... Moderator

    Yes, just to expand a little in case the point was missed. The way these parts are designed is so that the cylinder head always hits the front of the gearbox shell. This means that all the impact force from the piston is transferred through those two surfaces (cylinder head and front of gearbox shell). The pins were added after, when the cylinder head was already snug against the front, to stop the cylinder head from rotating.

    If you move the cylinder head back a bit, it will no longer meet the front of the gearbox shell causing the cylinder head to try and move forward every time the piston hits it. When it does this, it will be stopped by the alignment pins which means they will now be taking the entire force of the piston since there is nothing else to stop the cylinder head anymore.

    Make sense?
    -Spitfire- and Peeque like this.
  2. 1tonne

    1tonne Well-Known Member

    New Zealand
    So we can easily add 2 part epoxy and then moving the cylinder head back is then fine.
    So it may improve feeding.
    Doesn't seem too difficult either. Most people can use a drill, rotary tool and 2 part epoxy. And it is easy to plastic wield with a soldering iron. From what I can see it would only take about 30-40 minutes and then you never know, it may just work.

  3. 1tonne

    1tonne Well-Known Member

    New Zealand
    So I gave it a go. I used a gun that I have had feeding issues with for about 4 years. This gun has been such a frustration for a long, long time (Made up of all sort of parts that have not been totally compatible). Normally I could get it to feed up to about 20rps but once I change to a lower gear ratio, giving higher RPS, it would have feeding issues.

    The mod was easy but a little bit more involved than what I originally thought. First I noticed that I needed to remove 2mm of the tappet plate guide rail in the gearbox. Then I built the front of the cylinder head up with NeedIt (a hardening clay). Also, filed and sanded the NeedIt so it would fit nice. Then I cut the cylinder down by 2.5mm. Next I put 2 part epoxy glue on the front of the tappet plate fin. Since the tappet plate moved back further I also had to remove a little from the rear of the tappet plate otherwise it would hit the axle of the spur gear. Since I had built up the front of the fin, I also had to make sure that the low part of it did not touch the spur gear axle otherwise the air nozzle did not seat all the way forward.
    I also had to take half of a tooth off of the piston so that it would not get caught as the sector gear engaged.

    Anyway, after doing it and putting in 13:1 gears, it was able to feed 29-30rps easily using just a high cap mag. The mod means that the air nozzle can retract an extra 2.2mm. This means that the air nozzle definitely was not in the way when feeding. It also meant that the tappet plate seated in time for the for the piston to move forward. So overall, I am happy with the mod. I will do this again as it seems to work a treat.

    NOTE: All the gunk in the GB is from the filing. I will also be putting a mosfet back in it and also putting a hair trigger back into it some time.

    Attached Files:

    Chow likes this.
  4. 1tonne

    1tonne Well-Known Member

    New Zealand
    So the 2 part epoxy came off the tappet plate. -Annoying as it was working a treat.
    So I will today plastic wield some extra plastic onto the fin using a soldering iron and a spare piece of plastic from a selector plate. (I have done this many times on other plastic parts and it is stronger by far than 2 part epoxy).
    If this does not work, does anyone know where to get a V2 tappet plate that has a bigger than normal fin?
  5. Ben3721

    Ben3721 Active Member

    Well the thing is, if a nozzle pulls back way to far, the second bb may drop in too much and cause a delay as the nozzle has to push the pellet out of the way to chamber the first one. I basically have 1.5mm extra movement forward by just sanding the face of the tappet and a tiny bit of material where the sector shaft hits the fin, this works for me because I use short lip packings, most guns have the packing lips in the way of the hop up feed tube. From my experience shs tappets tend to have too much material on the tappet fin. But that may be with a issue certain shells.

    As for the cylinder head rotation lock pegs, I just drill out the holes a bit till the pressure is on the gearbox face rather than the pegs.

    I am able to hit about 38rps without feeding issues with a high caps on my m4, people have been able to hit up to 65rps perfectly fine with high caps for ak and m4. There used to be a list of feed rates on ASM before it went down. Some used sector clips for the ssg builds.

    I'll throw a video up in a bit on how I time my gearboxes and how I set them to feed. The only time I get miss feeds is when I forget to wind my mags.

    Edit: https://www.instagram.com/tv/CCCde_wnueb/?igshid=ros9h132sa8k

    Shooting video that has most recent part list too: https://www.instagram.com/p/CE0Vt2gnXGu/?igshid=9cvwrvr4x628
    -Spitfire- and kazuchan like this.
  6. Lefse

    Lefse Well-Known Member Supporting Member

    Good to see I'm not the only person that discovered the tappet fin and sector gear shaft thing. It can actually affect consistency significantly.
    -Spitfire- and 1tonne like this.