Demon spawn m16 from hell

[Spike]

Here's the story:

G&P M16VN

Ate it's original piston and gears. No problem. Replaced with a modify white piston and some King Arms gears. Shimming is perfect, AoE is perfect. It's supposed to shoot 350ish, but it only shot about 280.

-Perfect air seal
-very little leak in the hop up chamber
-did the tappet plate mod
-added a port to the cylinder

Now, it locks up in semi auto and the wires/motor get extremely hot, regardless of what battery was used. When fired in FA, the gun takes half to pull the gears really slowly and then fires like normal.

ideas?

*note: i found the 2nd and 3rd piston teeth have wear...but not the pickup tooth. wtf. Also, the pinion gear is showing wear.

[MaciekA]

Originally Posted by Spike

Here's the story:

G&P M16VN

Ate it's original piston and gears. No problem. Replaced with a modify white piston and some King Arms gears. Shimming is perfect, AoE is perfect. It's supposed to shoot 350ish, but it only shot about 280.

-Perfect air seal
-very little leak in the hop up chamber
-did the tappet plate mod
-added a port to the cylinder

Now, it locks up in semi auto and the wires/motor get extremely hot, regardless of what battery was used. When fired in FA, the gun takes half to pull the gears really slowly and then fires like normal.

ideas?

If I had the gearbox in front of me right now my two sanity-check passes would be the following:

1) Piston free-movement check. Remove the gears and spring, leaving only the cylinder and piston. Make sure the piston is in the home position in the cylinder. Now stick a long and very thin tool into your nozzle and check to see that the piston can be moved out of the cylinder towards where the spring guide usually sits. Now hold up the gearbox with the nozzle towards the floor and let the piston fall back down into the cylinder. It should move easily, if not with gravity then with at least a little shaking. I've seen your exact problem before where the piston was literally too fat for the gearbox it was in, intended to run at 360fps, running very hot and very slow, and losing tons of compression (260fps in that case). When checked, the piston took a lot of force to move up and down the cylinder by hand. It was surprising that the motor could even move it, though I was using a 11.1V lipo and neo motor to test

2) Check for anything that could be inhibiting the movement of the spur gear (or the other gears). I've seen an issue like yours a couple times, where in some cases the spur gear will catch on an overly-wide shim placed at the narrow part of the bevel gear, producing either very slow gear movement or a jam.

You should take your spring/spring guide/cylinder out of the gearbox, reassemble it completely, and carefully spin the gears very slowly with a tool, using only featherweight pressure. Try it with the gearbox flat on its side, try it with the gearbox standing up as if held in the gun, and try it flat on the other side. I've seen this exact problem evade a basic sanity check (i.e. "but the gears spun fine when I moved them with my fingers!"), so be very careful you're not missing something.

Hope that helps.

[venture]

I also have a couple of things I have found to be troublesome:

1) Modify pistons and tappet plates always seem to be too large/tight. I almost always file down modify tappets to be thinner on the edges so they don't jam in the gearbox. I have had a couple of incidents with Modify pistons where they jam at the rear most point of their travel. They were too tight in the gearbox and I had to remove a bit of the railings to get it to travel all the way to the rear without jamming.

2) If your new gears are shimmed just slightly too tight it can cause serious binding as the strain comes onto them.

[Dynamo]

check the rotation of the gears with out the piston. a friend of mine got a set of KA gears that wouldn't mesh together, and sounded like a wheel grinder when running.
if the gears run fine, then check to see if the piston is wedging it self between the sector gear and the top of the gearbox shell.

[venture]

Also, I don't want to say "told ya so", but I did say that you can buy the cheap stuff or the expensive stuff and you will find about a 10% quality difference for a 100% cost difference.

[Spike]

The piston being too wide is actually a very good probability... I dont' know why I didn't think of that. I'll try that next, thanks guys.


And Ron, we're at peace, you don't like modify, I don't like element, don't start that up again Besides, as soon as I get more cash flow I'm gonna start using SHS and Lonex parts mostly for standard repair jobs.

[Spike]

Well MaciekA, I just did what you suggested to check the piston movement... I'm pretty much certain now that it's too wide and has to be trimmed. It's really, really stiff in there.