New piston jams against sector gear!
 

Alright, I've been playing with this for hours now and no luck. I've searched a bunch and lots of people have similar problems but they aren't quite the same, so they haven't really helped.



I've got a v3 gearbox (AK) and the stock gears and piston just went on me. I bought a set of King Arms Normal Torque Flat gears. Also grabbed a Modify Quantum piston (That's the one with the full metal teeth).

What happens is as soon as the teeth on the sector gear touch the teeth on the piston, it all locks up. With the gearbox apart everything moves nice and free.. I even put all the parts into the right hand side of the gearbox to see if there was a difference, but it still ran smooth.

I've tried shimming how I normally do, shimmed left, shimmed right, didnt shim at all, same deal every fking time.

It looks like the teeth on the sector gear try to push the piston up against the top of the gearbox and that's how it's jamming. No idea why. The stock piston works fine with the new gears.



So, what the hell? :confused: Any suggestions?

Amos Airsoft how to: AOE and the ARS MASK kit! - YouTube

Part of the way through this I talk about checking the angle of engagement... That'll be what you need to do.

Hm, interesting, but I don't think that's the problem either. On the Quantum piston that tooth is actually already removed and thus the engagement angle is perfect.

http://arniesairsoft.co.uk/news2/wp-...5/image147.png

You may be locking up on the 2nd last tooth, go through the gear motions like in the video.

The piston may be too far forward in it's resting state, take the spring out and leave the piston in. Then rotate your sector gear and actually LOOK AT what's causing the jam.

You aren't trying to run a full tooth sector gear with a half tooth piston, are you? Would explain the piston getting shoved up into the top of the mechbox as soon as they start to mesh....

Yeah. I did. As I said, what seems to happen is the teeth push the piston upward a bit and it seems to get jammed against the top of the gearbox shell.
Like I said it all works perfectly smooth with the gearbox shells apart, only does this once I put it back together..


I don't think so. The piston has shorter teeth but it's not a half tooth. That picture above isn't a very good angle but the strip of steel that goes alongside the teeth is actually even with the crest of the piston teeth, not the root. The sector gear rotates freely through the half rotation where the teeth don't touch the piston and I did make sure I had it shimmed so that the teeth lined up properly left to right.

Yeah....that might be causing the problem. It's acting almost like a half tooth piston. That strip of metal is way too close to the gears and might be jamming them up. Not much tolerance for where the sector gear sits on the teeth.
It would be much better if that strip was flush with the piston, not the highest point of the teeth.

The pic above is what I thought I saw which is here:

http://www.airsoftgi.com/images/airs...ntPiston_A.jpg

Which requires a half tooth sector gear (unless the teeth are wide enough and offset on the piston to accomodate the full width gear.) This is one of the many issues people come across with mixing various brands of parts together.

Maybe I'm just mis-reading things?

Well, like I said with the sector gear turned so the teeth are down, it seems to rotate okay and the teeth seem to engage without touching the metal strip. I just tossed in another piston I had given to me along with another gun, and although the teeth on it are worn, it seems to jam the same way.:(

Oh, I should add, it isn't advertized as a half tooth, and the sector gear I am trying to use is the same width as the stock one and the modify torque set I have.. not even the modify gear works with the modify piston. >.<


Could something be wrong with the shell???

What brand of gun, what FPS, what motor, what battery are you using?

It's an src gen iii pro, aiming for 420 fps with a g&p m120 motor on a 11.1 lipo 1600mah 25c.

If you are wondering whether the motor and batt are just weak, I doubt it.. but I can't even get it to pull the piston with no spring at all, so.

the quantum piston is _supposed_ to work with full tooth gears.

are your guide rails smooth (enough)? ...if things are a little rough use some lube (that's what she said).
I've seen (although my google-fu is failing me atm) some v3 users glue a spacer to the top/back (open side) of their piston to stop it from binding.
G&P m120's aren't the torque-yst motors around. if you have something else on hand, give it a go (although that lipo probably fixes that).

you could probably just bring it to a tech nearby, if not just for a fresh set of eyes.

Heh, yeah, its a cheap motor but I wanted something with some speed.. but that doesn't even matter here because it won't even pull the piston with an m90 spring. As soon as it engages the teeth you can feel it lock up. It pushes the piston up and even when I go to open the gearbox it is hard to open because there is so much force pushing back down on the sector gear. It's almost like the teeth on the piston are a little too low, or the gear is a little too high. So confused...

Obviously you've seen where the piston gets pushed up from, but with more detail, are the teeth butting together like this >< or is the meshing fine? Would seem >< would raise the piston height as you see, which means the piston isn't positioned properly in the rails/cylinder............. have you installed anything that might make the piston sit a bit farther back than normal, say a Sorbo pad or something? What piston head did you put on there?

The teeth seem to mesh just fine.I just used the stock piston head because it seems decent enough. Could try a sorbo head though I guess.

It seems that with the gearbox apart it moves freely but I think it may still be pushing down on the sector gear a bit. It's seriously as if the teeth are just sitting too low or something. Maybe I should see if I can make a video of it to show you guys?

okay, video didnt work out well but here's a high ass resolution picture of it: http://img228.imageshack.us/img228/8643/imgp0587.jpg

Sorry for the shitty focal length, only lens I had handy..


Anyhow, just for kicks I put the piston in part way as shown in the pic and tried to close the gearbox. Couldnt even get it closed.. It's actually touching the flat portion of the sector gear and when I try to close it up like that, it pushes the sector gear down and then the bearings dont line up.


So yeah, definitely seems like the teeth are just too low. It's like this on the Modify 22.2:1 torque up gears and the King Arms 18:1 normal torque gears.


Did I just get a bad piston.. or.. something? Or does SRC use non-standard pistons with shorter teeth......?

SRC sectors seem to have taller teeth.. and shorter teeth on the piston... I had to do a sector replace on one recently .. the piston was in fine shape.. threw one of my spare parts sectors in, and it couldn't even touch the pistons teeth to engage.

src's seem to be slightly out of spec of standard "TM compatible" stuff

I didn't mention the Sorbo pad as a fix, I asked because it could be a problem as it could push the piston back a bit, enough to cause the gear teeth to not mesh properly.

Looks like you said in your pic, the size of the sector gear itself is the problem, or the piston teeth, I'd suggest actually filing down the teeth on the piston and custom fit it to the gears,

Ahh, dang. I almost want to buy a new shell then.. hmm..

Ummmm........ ouch?

If I was still into the gun tech stuff, I'd look at it for free and really diagnos it, but things being things, it's really freaking hard to deal with a new unusual problem based upon a couple pics and vague descriptions. I've solved some pretty odd problems in my former career as a gun tech, this one I'm baffled by and can't offer much more than I have due to not having mechbox in hand.

Nono, that's fine, and I appreciate all the help. I'm baffled too.. I'm a mechanical equipment designer and I'm still confused. :P

I just meant maybe I should buy a new shell because if this one has the sector gear positioned too high, I could potentially fix the problem by getting a standard TM shell.

I think you had a good idea about filing the teeth down though. Might just have to try that... The only other thing I can think of is to toss the parts in my TM version 6 shell and just see how they fit. I suppose if they did fit I could then assume SRC made a minor dimensional change compared to an original TM gearbox, and then at that point I might just buy a TM shell so I won't (shouldn't?) have a problem like this ever again. My only concern then is whether the TM gearbox shell would drop into the SRC frame properly...

SRC are not TM compatible.

Huh.. well I think we can say mystery solved here.. I didn't have much time to play with this today until just now, and I took a set of calipers to the sector gears. All have the exact same diameter.

BUT. Then I turned my attention to the piston. Here is a picture of them sitting side by side on a flat surface. Green one is the original, black one is the new one. http://img805.imageshack.us/img805/2868/imgp0593r.jpg


I don't think there's any way I can mill enough off the teeth to get it to mesh like it should, given that much of a difference in height. :(


So now I guess I need to try to figure out if I can just get a TM gearbox and have it still fit my SRC frame. I know the rest of the gun isn't TM compatible, but.. I don't really know what else to do now..

much easier solution would be to get a different piston and see if it helps.

also, the quantum piston's teeth are coated in titanium, so...good luck with that I suppose.

Yeah I know, that's why I wasn't relishing the thought of trying to mill it down. But after some googling around it seems it's a known issue that SRC guns don't take standard pistons, it's like the only non-standard thing in the whole gearbox. So my bad for not checking I guess. I never had any reason to believe they would use one non-standard part...


So, the quantum piston goes in my P90 and I'm ordering a stock replacement piston for the AK.

Actually just had this same issue on an LCT RPK that has an SRC mechbox
Lesson? Never buy anything SRC.

Issue here? SRC. Most if not all they're gearbox shell and other parts are off spec. It's a nightmare to install spec parts with SRC parts.