Version 2 Gearbox will not turn over.

SparkyDNut

I have been rebuilding my gearbox for sometime, and am getting frustrated by it now... When I put it back into the body of the gun ( King Arms Troy MRF-CX) and try turn it over, the Sector Gear engages the piston and moves it about 10mm, the tappet plate moves back a little and then it all locks up.
I have been setting the Sector Gear with the first tooth just above the tappet plate.
I have pulled the motor out of the grip and confirm that it runs fine.

I'm at the point where I'll be dropping it off to a shop tomorrow, but though I'd ask to see if you good folks have any suggestions..

Leftyflip

Are you sure the timing is set exactly right?
Is there any teeth missing on the gears or piston?
Did you shim the gearbox? If you did it could be too tight on one of the gears.
Ger.

SparkyDNut

The piston is new, and no marks on it, the one which I replaced had the first two teeth worn down, and the gears look fine too..
I did adjust the shim, I found that the sector gear was moving laterally in the gear box, I'll try undoing that...
As for timing the gear what do you us as a guide ?

Thanks...

Leftyflip

When you put the sector gear in place all the teeth should face towards the front of the mechbox, then the first tooth should be lined up with the first tooth on the piston.

SparkyDNut

Grand, so just about to pick up the piston... Doing it as I type... tks

Masada

Timing in a gearbox is actualy a myth. once you set the sector gear inplace so that its not engaging the gears then it'll be fine. anywhere between 1 and 5ish o'clock positions will be where you set it.
It sounds like you might be running into some other problem not connected with the timing of the gears.
How are you unjamming it?
when it locks up, can you push the piston back with a long thin screwdriver down through the air nozzle? If it moves freely by pushing it back then it could be the case that the trigger switch is un latching prematurely and causing the gearbox to lock back. this can be down to the cut off lever or the trigger block, whats the condition of those parts look like?

If it cant be pushed back then it would suggest the piston is getting jammed in the runners inside the gearbox. this can happen with some guns when installing ann aftermarket piston that might be minutely too wide. you can remove the cylinder from the gearbox and stick in the piston on its own for a dry run and see if its binding. if it is you can either junk the piston or trim it's grooves down slightly.,

Firekitten

not a myth per say.... just fixed....

If the nub on the gear isnt touching the tappet plate arm, then its grand.... It can only turn at one point, if they are on the teath already thats too far. If its not touching, it will only turn till it engages and then its fine.

Masada

It is a myth.

Once the gear is installed and not connected to the piston it will fire as its supposed to.

The gearbox will not go back together if the sector nub/chip is under the tappet plate. (any good tech will crank the gears by hand before actually re assembling the gearbox.)

This whole 1 o'clock thing is incorrect.

SparkyDNut

Firstly thanks all for the help so far.. it's much appreciated.

I've had mixed success.
I'm sure now that I had over shimmed, I have reduced them, and the box does go back together easier, and the gears are spinning some what better...
As suggested I removed the cylinder and checked the piston on it's tracks, and it does slide easily. (it is aftermarket)
In semi mode is it the cam on the bottom of the sector gear that tells the trigger to cut the power ? All wires and solders etc in this area look clean and in good condition.
At this point I reassembled partially, and it was firing well.. so I put the rest together and it locked up when I went to test fire some BBs
When I reassembled this time, I followed the guidance that the nub should not be under the tappet plate, this time the piston fired to the end but didn't quite get there... stuck on the last tooth...
On my sector gear, there is a plastic cam attached to the nub which pulls the tappet plate back earlier than on any other gearbox I've seen.. Googling this shows that it's something King Arms add to assist feeding on full auto...
I reassembled twice more, I got a screeching sound once, so I must have missed something on the re-assemble... Next time it went together better, however I think (could be wrong) it seems a little sluggish... It does now however run through a full cycle, I have not put a BB though it as it's getting late and I don't want to annoy the neighbors... So I'll check again in the morning..
Now I think I'll watch "Where Eagles Dare"

Masada

Sounds like your getting closer alright

That cam you talking about is actually called a sector chip or a delayer and it basically holds the tappet plate back fractionally longer than without one. it sounds like the problem you might have been having is to do with the shimming.,

When you shim the box you should remove the cylinder, piston, anti reversal etc and only have the spur gear in there to begin with.

You want to get as thin as possible a shim under the spur gear so as to allow it to spin without touching off the inside of the shell. This gear should be as low as possible. then you test the gear by sticking the shell back together (with only the spur gear in there) and see if theres lateral movement on it. if there is you compensate this by adding shims to the top of the gear. you want it to be as tight as possible without binding at all. (keep in mind when the gearbox is screwed together it'll be a little tighter so put some pressure on the shell as you are testing the rotation of the gear.)

Then you move onto the sector gear and this one you judge by its height over the spur gear where they meet. you want the gear teeth to mesh together but not for the flat surfaces of the gears to meet. when you have that nicely, you try the shell on there again and see if you need to add any more shims. if you do, you follow the same procedure as the previous gear.

Lastly is the bevel gear and like the sector, you judge this one off teh spur and set it so the teeth mate but not the flat faces of the gears. you dont want to have this one too low (unlike the spur) because the motor needs to mate with this one and it can be a bit whiney if its too low. again, try the shell back on there and see if you need any top shims in place and add then until theres no play.

With all that done, you can add teh grip of the gun without actually rebuilding it into teh receiver. you can test it out and get the motor allignment right here to be sure its shimed properly.

Motor Adjustment:
In most cases when you reassmeble the gearbox the gun can sound a little whiney because of the motor alignment. i usually adjust this by ear in semi, go in all the way and come out in half turns while trying to fire it and listening for the smooth sound. When thats done you switch to fully automatic and adjust the screw in more of a fine tuning fashion while listening carefully to get it right on the sweet spot.

Job done.

SparkyDNut

If only it's was as easy and you make it sound...

And do I feel like a numpty, for testing I've been putting it back in the receiver each time.. :rolleyes:

I think I'll start from scratch again tomorrow... I'm not going to let this one beat me..

Shiva

That post would make a good sticky on gearbox shimming.

Masada

SparkyDNut wrote: »

If only it's was as easy and you make it sound...

And do I feel like a numpty, for testing I've been putting it back in the receiver each time.. :rolleyes:

I think I'll start from scratch again tomorrow... I'm not going to let this one beat me..

lol.,
Well, if ya get nowhere with it, feel free to PM me and i'll arrange to have a look at it for ya.

Shiva wrote: »

That post would make a good sticky on gearbox shimming.

Good idea, infact, now that i tihnk about it, i don't think anyones ever described how exactly shimming works on here.

Shiva

Masada wrote: »

Good idea, infact, now that i tihnk about it, i don't think anyones ever described how exactly shimming works on here.

Me neither.....

Firekitten

Masada wrote: »

It is a myth.

Once the gear is installed and not connected to the piston it will fire as its supposed to.

The gearbox will not go back together if the sector nub/chip is under the tappet plate. (any good tech will crank the gears by hand before actually re assembling the gearbox.)

This whole 1 o'clock thing is incorrect.

Indeed, but that is still timing Masada.... Fixed or not, its timing, otherwise the gearbox simply wouldnt function. Its simple mechanics. that it has to be set 'precicely' or somewhere specific other than 'meshed with the piston' is the myth.....

What you describe yourself is timing, just your outcome is a little lost in translation, dispite the information being spot on....

Masada

its not timing, its simple mechanics alright, and I'm a mechanic, (maybe even a simple one ) but from my professional experience in timing various engines, cams, ignition systems etc etc, This is not timing and timing the gears is a myth.

Timing suggests accurate alignment in order for the process to run. this is not timing (most obvious in the fact that you cant do it wrong, it wont go back together if you have the tappet on top of the sector chip)

This is all going very off topic though, and not very useful to the thread.

Firekitten

Masada wrote: »

its not timing, its simple mechanics alright, and I'm a mechanic, (maybe even a simple one ) but from my professional experience in timing various engines, cams, ignition systems etc etc, This is not timing and timing the gears is a myth.

Timing suggests accurate alignment in order for the process to run. this is not timing (most obvious in the fact that you cant do it wrong, it wont go back together if you have the tappet on top of the sector chip)

This is all going very off topic though, and not very useful to the thread.

mmm, i'd debate the difference elsewhere... but hey, whats the point? life is too short to bother about the difference between eggs and bananas. I'll agree to disagree....


Best overall advice now... Check your batteries are charged, the motor isnt too high or low in the grip, and that the tappet is moving fully back and forth. If its cycling its one good thing! though sluggish can suggest over shimming again.... What lubricant have you got in there?

SparkyDNut

I think it's sorted... Will be able to confirm tomorrow...

So I went back to scratch and looked at everything again..
If it's fixed there were a number problems..

I had over shimmed, and in doing so may have caused problem two, one of the bushings was not spinning as freely as the others. So I re-shimmed from scratch, and replaced the bush. Gears are now spinning nice and free.

Next issue was the piston, when I fired it this morning, the piston went back but couldn't complete the cycle and on closer inspection it was catching the rail at the back of the gear box, i.e. it was not aligned as well as it should have been. So I took the dremel to the piston (systema aluminum) and opened the entry point ever so slightly and took a layer less than a mm off the guide rails essentially polished them.. The piston now runs the full length of the tracks solely by tilting the gearbox, yet is not loose in the tracks either.

Partial re-assembly, and the gearbox now cycles completely and feels/sounds what I would call normal... Will reinsert back into the body tomorrow and test fire..

btw Grease I'm using is the G&P set with the three different viscosities.

I'll post tomorrow, once I have it all back together, but I'm feeling positive this time.

SparkyDNut

Success, after re-assembly yesterday it ran for a few BBs and then jammed in the same spot, so I took a little more off the piston and opened the rails a little more on the end. With these changes it's working perfect.
Also thanks for the tip on the motor adjustment, I makes a huge difference.

Masada thanks a million...

Masada

Glad you got it sorted man.