Issue with the spur and sector gear jamming

[Jagd]

Hi guys,

I have some problem with my spur and sector gear jamming when I am turning them by hand freely in the shimming process (to see if it all spins freely). The thing is that it blocks at one point during the rotation and I have to use some force to pass that section so that it can continue to spin freely.

Obviously I have a problem, but I really doubt that it is related to the shimming process cauz I tried all kinds of combinations.

My gun is a CYMA AK 105. So far I have almost changed everything stock for modify parts. All except the gears and the piston plus the cylinder. The funny thing is that it was working like a charm and silently right before I started changing the parts.

I am wondering if the nylon bushings are not there for are reason. They are there because that the tolerence of the 2 receiver is really bad and that the bushing holes maybe do not aligned perfectly. So with nylong bushings the nylon can be deformed slightly and compensate for that, but when you upgrade for steel bushing you have a problem. I even had to do a really minor filing job because some of the holes where a bit too tight for the steel bushing (with nylon bushing since it can be squeezed a bit that was not a problem for them to put them in the receiver)

So since with steel bushings the holes does not align perfectly and it can cause a problem with the gears.

Either that or I have crappy gears that are not dented properly are not entirely flat and they kind of wobble when I turn then and it jams at some point.

What do you guys think is the problem?

[incrediboy729]

I had a similar problem with my gears, ended up having like 3 bushings on one side of the sector gear, one on the spur, and 1 on the bevel. Make sure that the gears aren't getting pushed diagonally. Sometimes the gears don't fit perfectly in your gearbox, which results in the sidewalls of the gears hitting and turning the sector gear diagonally, thus causing it to lock. I'm sorry if this sounds confusing, but it's the best way i can explain it.
Do you have the gearbox screws tightened when you are doing this test?
Also check your cut off lever and make sure it's not getting in the way.
Hope this helps.
-Brett

[Jagd]

Originally Posted by incrediboy729

I had a similar problem with my gears, ended up having like 3 bushings on one side of the sector gear, one on the spur, and 1 on the bevel. Make sure that the gears aren't getting pushed diagonally. Sometimes the gears don't fit perfectly in your gearbox, which results in the sidewalls of the gears hitting and turning the sector gear diagonally, thus causing it to lock. I'm sorry if this sounds confusing, but it's the best way i can explain it.
Do you have the gearbox screws tightened when you are doing this test?
Also check your cut off lever and make sure it's not getting in the way.
Hope this helps.
-Brett

Yes I screwed the gearbox before testing that the shimming job was ok. The cut off lever too.

I don't understants what do you mean by:

ended up having like 3 bushings on one side of the sector gear, one on the spur, and 1 on the bevel.

Did you mean shims instead of bushings? otherwise it does not make sense.

Sometimes the gears don't fit perfectly in your gearbox, which results in the sidewalls of the gears hitting and turning the sector gear diagonally, thus causing it to lock

Looks like it is the problem that I have, so how do I fix it?

[m102404]

This is a relatively common issue with clones and crap-so so guns...I haven't seen "good-old" brands have wonky shells like this. Because of the wonky specs, they're not worth upgrading/modding/tuning/repairing. Well...sort of worth it, but they are a pain in the ass.

Buy a new mechbox...a new cut off lever (a lot of clone ones are just weirdly off a bit). Buy an extra pack of shims too.

If that doesn't work...consider buying a new mechbox...because the time/money troubleshooting it might be enough that it's just not worth trying to make it work.

If you want to fiddle and build a good mechbox...start with good parts. If you just want a mechbox you can shoot...just buy another clone one and toss it when it blows up (some last a long time...others don't). Then just swap in a new clone one.

A good, well built mechbox will cost you about $200-300. A clone one will run you $75-90.

[CDN_Stalker]

Could also be a chipped gear tooth, burrs on the gear teeth, shimming not done right to separate the gears properly.................... these are all things I've found in the years I did gun work, and often times they were quality gears (Systema I've found to have really bad burrs as an example) that were causing problems.

[Jagd]

So probably my best option would be to bring it to a gundoc for a diagnostic, before putting some more money into this.

[CDN_Stalker]

Ya, it wouldn't hurt, and at least you would have spent your money wisely (depending on who you get to check it out). At least it could zero in on the problem area and allow you to buy exactly what you need to replace, instead of just filling your mechbox with dollar bills.

[Jagd]

yeah because buying new gears is one thing but buying a new mechbox plus new bushings...well it adds up quite a bit...

[incrediboy729]

Did you mean shims instead of bushings? otherwise it does not make sense.

Looks like it is the problem that I have, so how do I fix it?

You are absolutely correct, my bad. Very sorry. I meant shims.
And to fix the diagonal problem, you honestly are just going to have to spend a lot of time experimenting. I drew a picture for you, hopefully that should help you. But basically you might need to add or take a away shims on the gear that's being pushed diagonal to correct. Then after it's been corrected, you can fine tune all the other gears and play with different combinations.
I had the same problem with a pair of G&G helicals. The sector gear ended up getting pushed way diagonal, so i added shims to one side to correct.
Hope this helps.
-Brett

[Jagd]

The thing is that when I try and spin the gears without the other half of the receiver on everything is cool, it is really when I put the other half on, that the sector gear jams

When I try with the spur and the bevel only (mechbox closed) everything spins perfectly fine. Also I am pretty sure it is not a shimming problem, because I tried all kind of different configuration of shims (I have a pack of modify shims that give 0.1, 0.15, 0.3 and 0.5 mm)

So it really comes down to either the gear or the mechbox. Maybe the gears shaft is not big enough for the bushing and there is some play. Or not entirely straight and being forced into a certain position (because I am closing the other half of the mechbox) the gear (either the spur or sector) tilt slightly diagonally which in turn cause a jam.

But it is not an instant jam either, I am able sometimes to spin the sector gear 1 or 2 full rotation before it jams.

[CDN_Stalker]

Surface area of the sector and spur gear, how much space do you have between them? Chances are they are being pressed together, in which case you'd take offf one shim from the to pof the sector gear and put it on the bottom, then try the closed mechbox again til you get it unjammed. most likely, but could be something else. And avoid following a shim guide as to where to put what thickness of shim, it rarely works, and there are different tolerances between parts, especially mixed and matched brand parts.

[Jagd]

Originally Posted by CDN_Stalker

Surface area of the sector and spur gear, how much space do you have between them? Chances are they are being pressed together, in which case you'd take offf one shim from the to pof the sector gear and put it on the bottom, then try the closed mechbox again til you get it unjammed. most likely, but could be something else. And avoid following a shim guide as to where to put what thickness of shim, it rarely works, and there are different tolerances between parts, especially mixed and matched brand parts.

I think you nailed it right there, they are probably getting pressed together. so in regards to the spur gear, should I recheck the shimming of this gear? or it is really only about the secto gear? Pardon me for my being a total noob, but what make it so that a higher sector gear prevent both gear from being pressed together?

Edit: I am trying all sorts of shimming combination and it does not work... ;-( I will have to find a local gundoc a.s.a.p

[CDN_Stalker]

Originally Posted by Jagdalex

I think you nailed it right there, they are probably getting pressed together. so in regards to the spur gear, should I recheck the shimming of this gear? or it is really only about the secto gear? Pardon me for my being a total noob, but what make it so that a higher sector gear prevent both gear from being pressed together?

Edit: I am trying all sorts of shimming combination and it does not work... ;-( I will have to find a local gundoc a.s.a.p

Spur gear should be raised a slight bit off the bushing. Sector gear needs to be raised enough off spur gear to clear it. I've had the same issues with you before, and was all because of too many shims on top of the sector gear, putting them mostly on the other side, and having a little side to side movement of the sector gear is good. Try it a few more times on your own, then when really frustrated, gun doc. Am sure you'll get it by yourself, you seem to have most of the gears shimmed right, so why let the sector gear beat you? Especially when I just gave you the info about side to side movement, about 0.5mm and clearing the spur gear surface is a good thing. Shimming is all about feel and eyeballing, is why I said to avoid shim charts.

[Jagd]

Originally Posted by CDN_Stalker

Spur gear should be raised a slight bit off the bushing. Sector gear needs to be raised enough off spur gear to clear it. I've had the same issues with you before, and was all because of too many shims on top of the sector gear, putting them mostly on the other side, and having a little side to side movement of the sector gear is good. Try it a few more times on your own, then when really frustrated, gun doc. Am sure you'll get it by yourself, you seem to have most of the gears shimmed right, so why let the sector gear beat you? Especially when I just gave you the info about side to side movement, about 0.5mm and clearing the spur gear surface is a good thing. Shimming is all about feel and eyeballing, is why I said to avoid shim charts.

Well dude I am gonna retry it's not rocket science FFS! And I am failry good with the manual mechanical stuff. I have stripped down my AEG pretty easily and understood the way an AEG works quite easily but this sector gear drives me nuts!:rrr:

I even removed everything from the gearbox even the cut off lever. So I have the 2 halves naked just to be sure that nothing interfere.

I have an Ver3 Mechbox. So I started with the spur gear and added a 0.15 shim (with the 0.10 it was grinding just a little on the mechbox wall) at the bottom. After that I added quite a few shims on top 2x 0.5 (otherwise there was significant left and right movement) so I screwed the mechbox and the spur gear was spinning perfectly fine and quietly

So I tried with a 0.3 at the bottom of the sector, with 0.4, 0.5. and different combination of shims for the top and dude...the same crap. it spins sometimes a full and a half rotation, than it jams..I have to apply a good amount of force to make it spin again.

The problem happen when I am putting the 2 halves together and I am trying to spin the gears.

I am just wondering if I am not getting a set of Marui gear (Not worst than the CYMA gear I assume) and not expensive if that would solve the problem. They are selling 12$ a set on Red wolf and I have to order other stuff anyway. What do you think?

EDIT: After cleaning the 2 mechbox halves and taking a good look at the 3 holes for each half where the bushings go, I noticed that the holes are not exactly at the same place so maybe it's just because of the crappy quality receivers that does not properly align when I close the mechbox, it's almost impossible that it is the shims because I treid about everything in terms of combination.

[opml]

i know this thread is ancient, but i had the same problem and i fixed it so ill show you fro anyone who looks here later.

i have this exact same problem but what the problem is, is the misaligned bushings in the shitty gear box shell.

https://drive.google.com/file/d/0B3p...ew?usp=sharing

in this image I've shown that i filed down the one side of the wall that holds the bushing inside the mechbox

https://drive.google.com/file/d/0B3p...ew?usp=sharing

in this image i show you that after i have filed down the other side your bushing is just gonna fall out and wiggle around so you push it to the side you want it to and fill that space left with super glue. if your worried about not being able to knock it out then leave the grease from you mechbox on the walls, and the bond between the bushing and walls will be strong but not unbreakable.

this fixed it because the sector gear was rubbing against the spurr. By moving the bushing into the right position i was able to fix this problem, and the gears are butter smooth now! cheers and happy teching.