Need some help with some fixing/tuning!

[GODSPEED|seven]

Hey,

I have a Classic Army UMC (HK UMP) that NEEDS:
1. some fixing up
2. a tune-up
3. if possible some upgrades towards simulating the real UMP.

Here are the upgrades I've already done to it:

- I've removed a small part of the lip inside the upper body (very tiny strip that was litteraly useless) to install the ASGI 9.6V 1650mAh battery.

- Prometheus 6.03 208mm Tightbore Inner Barrel

- Prometheus Soft Hop-Up Rubber Sleeve

Everything is VERY consistent and it's VERY accurate.. but to go on with the main topic at hand:



1. FIXING NEEDED ASAP!

Motor Cage/Mount is defective:
The screw to adjust the motor height doesn't work the way it should.. I need a new cage/mount. (I believe the UMP uses a G36 Mechbox and motor cage).

Piston is about to be useless:
A tooth neer the middle of my piston is broken, and the other teeth are getting grinded away.

EXTREMELY Noisy:
Yeah.. the gun is VERY noisy, it's almost scary. I've tried shimming it many times. I bought some Sticky-G gear grease.. I followed most guides for shimming, I'm pretty sure I couldn't get it better.. but the motor is also VERY noisy.

I shimmed the gears so that there is no contact with the middle gear on the back of the gearbox, and they aren't loose (if I try to move them up and down on their axis, they don't really move) but they also turn quite easily, i can easily turn them with my finger with no need to force them at all.

The motor is another story, it's quite a noisy Classic Army motor, it was defective after my first 500 rounds (when i purchased the gun new 1 1/2 years ago. It seemed to be missing contact on one of the copper looking parts, so I tapped it in with a hammer (slightly) and it's been working flawlessly since, but noisy.


2. A TUNE-UP

I want to hear the distinct sound of the 'POP' 'POP' 'POP' from the air compression... not from the gears and motor!

Getting rid of the grinding noise:
Very simply, I don't want to hear anymore grinding noise like it's going to break..

So I was thinking of getting the Modify SMOOTH Modular Gearset 7mm V2/V3 - NANO Torque and either one of these motors:
- Tokyo Marui EG700 Motor
- Tokyo Marui EG1000S Motor
- Systema A to Z Motor

I hear the TM motors are quite quiet, and I have a EG560 Motor in my MP5, and It's much quieter than my Classic Army Motor.

Systema I've always heard are kind of like the top of the top, and they advertise this motor as very quiet.

Getting the proper piston:
I do not know if I should go for a piston that has full metal teeth or not..


3. UPGRADES TOWARDS REALISM

Simply put, I want to have approximately the same rate of fire that the real steel UMP has.

I know if I go back to my 8.4v Stick batteries, I will have that rate of fire I am looking for... but the trigger becomes sluggish and response is SLOOOOOOOWWW. I wanted the 9.6v for a quicker trigger response.. and even then, it could use a quicker responce. I would like to be able to shoot as fast as I can pull the trigger.. which is VERY far from being the case.. if I try that, half the shots don't happen because the cycle is too slow. Would for example a 7.2v Li-Po be the cure to my issue without adding too high of a RoF??

I am NOT looking for more power! Stock, it was 360 FPS; with my new inner barrel, I am not sure.. but I would rather stay within 330-380.


So, in conclusion, I would really appreciate some tips towards the proper parts for fixing, tuning and upgrading my gun.

PS* - I BELIEVE THE UMC USES THE SAME INTERNALS AS A G36.. IT'S A V3 GBox. BUT IF SOMEONE HAS A GBox ON HAND , I WOULD LIKE TO COMPARE MEASUREMENTS TO MAKE SURE ITS THE G36 GBox.
TO BE MORE PRECISE, THE DISTANCE FROM THE FRONT TO THE HOLE WHERE THE PIN THAT HOLDS IT INSIDE THE LOWER RECEIVER FITS.


Thank you!

[GODSPEED|seven]

BUMP! (lol.. I do need some help here!)

[MaciekA]

Hi,

I have the NANO gear set, and it's actually by far the loudest gear set out of all my AEGs. You get relative ease of installation but you are paying 3 times more than you really need to just to avoid shimming. Really, only get these if you are paralyzed with fear of shimming. If you understand how to adjust your motor height to the bevel gear and shim from there, you will end up with a much nicer result, and far quieter. In addition, if you want to lower RoF, you may wish to aim for a gear ratio that will yield even less speed.

I have the SHS 300:100 gearset (if you have doubts about this brand, just buy the King Arms 300:100 gears, it's the same as these gears but with a King Arms logo on it). These are triple torque gears and the ratio is 26.43 :1, which will give you an even more relaxed RoF than the 22.1 : 1 of the NANO set. They are also by far the quietest gears I have. The C8 I have them in definitely has the compression-and-nothing-else pop pop pop pop sound -- I'm super pleased with the sound. Note however, that these are helical gears and you will have to shim them very carefully. I spent a LOT of time shimming these (with the smaller-diameter Modify "advanced" shims, which easily fit into the diameter of the inner race of the bearing bushings in the G&P mechbox), used PTFE grease, and made sure to shim from the bevel. Sounds great.

If you are a little unsure about helicals and want low RoF you could try the 32:1 SHS gears:

http://torontoairsoft.com/product.php?id_product=1206

And yeah, a 7.4 LiPo will probably give you the snappiness you want without the high RoF. That's what I stick with in my guns. For really inexpensive high quality ones go with hobby king.

By the way, I do think you're right that the UMG uses a V3 gearbox. I think if anything mismatched it might be the nozzle, cylinder, and motor cage, but I could be wrong. These things are easily replaced.

Good luck

[MaciekA]

BTW, if you want to post high-res pictures of your gearbox, go ahead, I can compare against my G36.

[GODSPEED|seven]

Originally Posted by MaciekA

Hi,

I have the NANO gear set, and it's actually by far the loudest gear set out of all my AEGs. You get relative ease of installation but you are paying 3 times more than you really need to just to avoid shimming. Really, only get these if you are paralyzed with fear of shimming. If you understand how to adjust your motor height to the bevel gear and shim from there, you will end up with a much nicer result, and far quieter. In addition, if you want to lower RoF, you may wish to aim for a gear ratio that will yield even less speed.

I will need to start by getting a new motor mount.. because my motor height adjustment is 'screwed', so I cannot precisely adjust it. Also, i have to adjust it very high, or else it slips off the gears... maybe i haven't shimmed the bevel gear right..

Actually maybe I need a few lessons in shimming.. because I never started with the bevel gear :\

Do you maybe have a few tips for me? How do I know if I have the right shim spacing for the bevel gear?

If you are a little unsure about helicals and want low RoF you could try the 32:1 SHS gears:

http://torontoairsoft.com/product.php?id_product=1206

And yeah, a 7.4 LiPo will probably give you the snappiness you want without the high RoF. That's what I stick with in my guns. For really inexpensive high quality ones go with hobby king.

Ok, on eHobbyasia, when I look up a helical gear set, it recommends I use a higher volatage battery, like a 10.1v.. would a 7.2v li-po do the trick?

..and will a 7.2v li-po stress my internals more than a 9.6v battery??

By the way, I do think you're right that the UMG uses a V3 gearbox. I think if anything mismatched it might be the nozzle, cylinder, and motor cage, but I could be wrong. These things are easily replaced.

Yes, it is a V3, and I am quite sure it can only be the G36 style, because of the body types and the fact that on both guns, the gbox is held tight to the lower receiver by a pin.. unlike the AK gbox.

I would almost like to find a whole good quality gearbox.. unfortunately I do not think SYSTEMA makes G36 gearboxes..

I will take some pictures later tomorrow or during the week when I have a chance to do so, thanks for the help!

[MaciekA]

Originally Posted by GODSPEED|seven

Do you maybe have a few tips for me? How do I know if I have the right shim spacing for the bevel gear?

I do roughly the same thing I do with V2 shimming except the V3 gearbox makes it easier:

You know how your gearbox shell splits into two, and whenever you work on it you always lay the right half of the shell (the "starboard" half) aside and leave it alone until it's time to put it back on? What I do is I put my bevel gear in *that* half of the gearbox, alone with no other gears or bushings, and then attach the motor cage. Once the motor cage is attached, I adjust the motor to its lowest height possible, away from the bevel.

Then I slowly raise the motor bit by bit, making sure that the motor cage is held in the place it would be if the entire thing was put together (important! especially if it's not tight). I move it up slowly until it starts to mesh with the bevel. At this point, you should have no shims on your bevel yet. Let the teeth mesh and rotate the bevel into the right position to accept the pinion. However, make sure the pinion isn't pushing the bevel UP. If it is, lower your motor, put on a shim, and start again. Do this until the bevel is no longer disturbed by the pinion, but they still mesh perfectly.

After that, put your bevel gear into the other half of your gearbox shell. Now remove the motor cage as well. Test the play and free rotation on the bevel gear (with no other gears in the gearbox). Add shims on the bottom of the bevel (the opposite side from the shims you placed in the paragraph above -- leave that other side alone as it is perfectly aligned with your motor). Make sure to tightly screw the shells together at this point when testing your shimming.

Now shim the spur gear as low as possible but enough to clear the contact with the bevel (aside from the meshing teeth of course). Test for free rotation and contact, again, sealing the gearbox first. Don't be afraid to get down low and physically look at the gears to see if they're making good contact. I like to seal the gearbox and actually look into the motor's entry point to look at the gear mesh between the spur and bevel. Use a BRIGHT flashlight. Shim the top of the spur gear to finish that up. Test again.

Now finish with the sector, again, as little height as you can get off the left side of the gearbox but enough to clear the cutoff lever and the spur gear. Make sure not to shim it too high or the tappet plate could have issues, and you could make poor contact with your piston.

I like to load up on lots of thin shims (the modify advanced shims are great) and take as much time as I need to shim, so that everything is adjusted in very small amounts, especially when I'm approaching the ideal shim point for a gear.

An assorted list of goals off the top of my head:

1) Ideal pinion + bevel meshing *first*. Motor's pinion should NOT disturb the bevel when it is raised into the gearbox assuming the gears are rotated into a mating position (check this as many times as necessary, be creative and meticulous with your methods if possible. I've even "marked" the teeth with grease and pushed them in and then inspected the pattern in the grease to see how the meshing is doing).
2) As little play as possible in the gears, but at the end you should still be able to nearly feather-touch the sector gear and move all the gears (with gearbox sealed). This will change a little bit when you've got your ARL in since it will be clicking away as you rotate.
3) Each gear only meshes with its sibling gears on the teeth with no other physical interaction.
4) Ensure ARL is aligned with the bevel before assuming you're done (I made this mistake recently, this is what the result looks like: G&P gearbox debugging - YouTube ) .
5) Check angle of engagement with piston at 12 o'clock before assuming you're done (a common source of shredding and problems). If the sector engagement to piston engagement looks more like 2 o'clock instead of 12, you may wish to correct this with a sorbo pad or similar. If your gears and piston are stock this will probably not be too far off though.
6) If you have time, and you should make time, run your gears and everything with the motor in but without any compression components in there (no spring, cylinder, tappet plate, etc -- just gears). Compare the sound of shimming attempts as you go, it can tell you a lot.

Check all the assumptions above over and over as you work your way through it. I often make a mistake later in the shimming that invalidates the results of everything I've done up to that point (like shimming the sector too high because I've shimmed the previous gears too high, etc).

Originally Posted by GODSPEED|seven

..and will a 7.2v li-po stress my internals more than a 9.6v battery?

No, LiPos are fine. Stick with 7.4V batteries and you'll be OK.

Originally Posted by GODSPEED|seven

Yes, it is a V3, and I am quite sure it can only be the G36 style, because of the body types and the fact that on both guns, the gbox is held tight to the lower receiver by a pin.. unlike the AK gbox.

If it helps, I noticed that there was a guy that used a UMG gearbox in an AUG with minimal effort.

[GODSPEED|seven]

By the way here are the links to 1024x768 pictures of my gearbox:

CA UMC Gearbox (Right side)

CA UMC Gearbox (Left Side)

Measurement from Pin Insert to front


By the way, I thank you very much for all those earlier tips; I was getting a little tired of working on my GB to no avail. I just worked on it for about 3-4 hours. I already had some Modify Advanced Shims & I also had some Modify High Speed gears I decided to try out.... I've never shimmed it this well!

I heard Modify gears are loud... but ha! if this is loud, I can't wait to get quiet gears!!

What I most appreciated is the these gears seemed to be much higher quality, especially in finishing.. the spur gears edges we're all rouded off to avoid shredding metal and stuff, while my classic army ones we're really square. The sector gear, well the part that engages the piston, has it's teeths slightly rounded off as well, and the finish is really smooth.. I guess it helps prolong the pistons teeth longer.

A pro coould probably shim to tighter tolerances, but I could barely - really only a micron - move the gears up and down on their axis.. adjusted the bevel gear to match the motor height.. then I went step by step like you suggested.. next the pinion gear, then the sector gear!
Everything fit perfectly, and the tappet plate still has a 1/2mm of play.

I swear it sounds NOTHING like before! To hear the friction at all, I have to put on the suppressor (which suppresses a hell of alot), so I adjusted the motor with the suppressor on. While there is the sound of friction, I believe it's the crappy motor, because the gears are wonderful.. and maybe a little too fast for my taste..

16.1:1

eesh, with a 9.6v... I'm almost worried my piston won't last much longer.. ha! Seeing it's the stock piston and only has 1 metal tooth at the back.



I'm just wondering if you could maybe give me some input on Pistons.. I'm really thinking of going with a all-metal teeth piston, although I'm worried it may be noisier? maybe maybe not, you seem to have some experience toying with internals..


Hey, I do not know how to thank you for the time you took to reply to my issues and all that help, it's much appreciated!

[MaciekA]

Good to hear you're having success with your tuning.

I'm not an expert in pistons, it's an area of relative mystery to me, but I do know that if:

1) you have your gears set up properly and
2) have a good angle of engagement (AoE), and
3) have filed down the second-to-last tooth if necessary (or even a bit of the third sometimes) and
4) your piston isn't a dud,

.. then your piston should last you a long time. Inspect your piston ... how is the wear and tear on the teeth at the moment? Run your fingers along the teeth to check if there is a wear pattern that shows where the sector has stripped the piston. I've opened up my own and friend's AEGs and seen a few types of wear patterns so far, ranging from a long stretch of stripped teeth from the front to rear of the piston, to only the first 2 or 3 teeth on the rear of the piston (near the spring guide), to damage near the front of the piston where the metal tooth is.

Here is a Madbull piston from my Diablo with a fun wear pattern:



When I got this piston I decided to just shove it in the gun and run half a bag of BBs through it in a day of play. The gun was firing 25 rounds/sec, 360fps with a G&P M120 motor and the Modify NANO gear set. It sounded pretty nasty. In the picture above you can see 3 of the teeth near the rear of the piston are being shredded like a carrot after that single day of play.

After doing this post-mortem analysis, I went ahead and filed down the teeth to match the wear pattern the sector gear "wanted": i.e., the first tooth was filed down a lot, the second tooth about half, the third tooth just a tiny bit.

I then tested the engagement with my sector gear. There hasn't been any additional wear on the piston and the gun runs great (aside from the self-shimming gear set sounding a bit noisy -- writing this post is tempting me to go take them out and re-do the gears with shims ). I wouldn't recommend using this method to find out which teeth "want" to get filed down, but hey, I certainly learned a bit from doing it, it was fun, and pistons are cheap!

[lurkingknight]

looks like you're well on your way to fixing a lot of your issues. lots of noise can be generated from improper motor height, and all motors sound a little different. my g&g high torque sounds a lot quieter than my guarder high torque.

I just recently installed 2 full metal rack pistons in my m14 and p90, I haven't been able to put as many rounds through them at all, but I've corrected both for aoe, we'll see how they do next year. The thing about full rack metal from what I understand is that it will last longer, but if something breaks, it's usually the gears that go... which would you rather replace, 20$~ piston or a 100$~ gearset? I would think that if you corrected aoe for either plastic or metal rack, you'd be fine either way, unless you railed on the gun in full auto when it was mechanically jammed, then that's not the fault of the parts.

if you're going to use a 9.6v battery for the trigger response and want to reduce your rof, you'll need a computerized mosfet that has programmable motor speed. It will slow your rof down without effecting anything else, also you'll get the benefit of preserving trigger contacts and all that other great mosfet stuff. Only problem is, those computerized ones are a ton more expensive than standard mosfets, but you can even put your 8.6 back in and get the same trigger response as your 9.6, or like it was mentioned, 7.4 lipo.

[MaciekA]

Originally Posted by lurkingknight

The thing about full rack metal from what I understand is that it will last longer, but if something breaks, it's usually the gears that go... which would you rather replace, 20$~ piston or a 100$~ gearset? I would think that if you corrected aoe for either plastic or metal rack, you'd be fine either way, unless you railed on the gun in full auto when it was mechanically jammed, then that's not the fault of the parts.

I've experienced this in my G&P C8, twice. Full metal piston, gearbox jam, snapped the shafts on the gears clean off. I wish I had spent some time inspecting it and the AoE first before running it stock out of the box. Live and learn, it's running a fully plastic piston now and is a happy gun.

Originally Posted by lurkingknight

if you're going to use a 9.6v battery for the trigger response and want to reduce your rof, you'll need a computerized mosfet that has programmable motor speed. It will slow your rof down without effecting anything else, also you'll get the benefit of preserving trigger contacts and all that other great mosfet stuff. Only problem is, those computerized ones are a ton more expensive than standard mosfets, but you can even put your 8.6 back in and get the same trigger response as your 9.6, or like it was mentioned, 7.4 lipo.

The Burst Wizard is actually really cheap (I got mine direct from the guy that makes it for 35 bucks) and can do RoF reduction, but I hear that reducing RoF (and the BW's documentation also warns about this) can really tax your motor greatly to the point of damage. Playing with ratios and reducing voltage is probably a better idea.

[lurkingknight]

yes, I've heard burst wizard is not mosfet compatible either, so if you want to install a mosfet later BW will have to be removed.

imo, if I put a lipo in the gun, I want that auto voltage shutoff on the triggermaster/ cheetah 2n to be safe. It's an added layer of security. But if you're never going to a lipo setup, a simple 20$ mosfet will prevent trigger contacts from burning and give a snappier trigger on lower voltage batteries.

[m102404]

IIRC...you're going to be hard pressed to put a computerized MOSFET unit in a UMP, without resorting to external battery/PEQ boxes and stuff like that. I don't think that there is space inside otherwise.

There migh be room for some of the "simple" thumbnail sized mosfets that just protect the trigger contacts, but that's not really doing the trick for you then.

Unless you go with a computerized full-feature MOSFET like the triggermaster III....you're stuck. You're going to give up on one or the other....quick trigger response = high ROF....slower ROF = slower trigger response. That's just the nature of the beast with AEGs.

You can alter/affect it with different motors, gear sets, springs...but at the end of the day simply trying to find a happy medium is about all you'll get.

A lipo will be able to supply a burst of power better than other battery types....but not so much that you'll get the instant trigger response but not the high ROF. Voltage is Voltage...Amps are Amps.

[lurkingknight]

if he's got room for an 9.6, he's probably got room for a cheetah 2n and a 7.4 lipo but then again, hard for me to say without having it in my hand, the cheetah 2n is a little wider than a AAA battery and about as long, little longer after the wires are all attached.

[MaciekA]

Yeah I agree if there is room for a 9.6 there is plenty of room for a Cheetah or similar circuit, plus a 2 cell LiPo... but it would probably have to be smaller than 1000mAh to co-exist with a Cheetah.

But there are 800mAh batteries on hobby king that can fit into some truly tiny spaces.. so this is a worthwhile investigation.