New piston jams against sector gear!

[CDN_Stalker]

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?

[XZIVR]

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?

[XZIVR]

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......?

[Reckless]

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

[CDN_Stalker]

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,

[XZIVR]

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

[CDN_Stalker]

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.

[XZIVR]

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...

[Slow]

SRC are not TM compatible.

[XZIVR]

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..

[wind_comm]

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.

[XZIVR]

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.

[ThunderCactus]

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

[HKGhost]

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.