I have new bushings of a different brand in a build of mine, and painstakingly enough I have tried to shim properly, but probably messed up somewhere. I get an awful screeching sound when firing the gun.
I want to know which gears are most likely to be the ones making the noise? I have a suspicion that it is the bevel and pinion gear interaction. All my gears spun smoothly when I rolled them together inside the gearbox before full assembly, so the only new factors would be the metal piston teeth, AR latch, and pinion gear.
Screeching gearbox
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captainkirk05
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Skywalker
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Re: Screeching gearbox
As long as it isn't shimmed too tightly, I would assume noise to be coming from improper motor height.
Don't forget to check that the gears roll smoothly while holding the gearbox in all orientations. Ideally, the gears can't slide along the axles at all, but sometimes that is hard to notice without holding the gearbox on its left side, and flipping it over to the right, spinning the gears in each orientation.
Don't forget that even a 1/4 turn of motor height adjustment makes a big difference, so don't go turning the set screw 3 revolutions without test cycling along the way.
Don't forget to check that the gears roll smoothly while holding the gearbox in all orientations. Ideally, the gears can't slide along the axles at all, but sometimes that is hard to notice without holding the gearbox on its left side, and flipping it over to the right, spinning the gears in each orientation.
Don't forget that even a 1/4 turn of motor height adjustment makes a big difference, so don't go turning the set screw 3 revolutions without test cycling along the way.
[align=center]I'm here to hate your M4[/align]
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captainkirk05
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Re: Screeching gearbox
Fixed it. It was a mix of the bevel gear being shimmed to high into the pinion gear, as well as a crappy Magpul MOE grip that wouldn't let the motor height adjust where I needed it.
Re: Screeching gearbox
HaHa.
I bet I know what gun this is.
If it is the one I am thinking of.....
- No matter what gun you shim, remember the bottom of the gears is for setting the height of the gears.
The top of the gears is for controlling the amount of Play.
- Make life easier on yourself.
Shimming KWA Gears paired with 5KU 9mm Solid Bushings is one of the most difficult shim jobs in all of airsoft.
It literally might be the toughest task of shimming out there, so don't be discouraged.
I can count on one hand at best the number of Techs in the USA that could pull it off using Bevel/Pinion Method and actually get it right, and no one at KWAUSA Inc. can even do it.
So, I do not recommend Bevel Pinion method unless you are already experienced with it and know what you are doing.
Make life easier on yourself. A shim job following the principles of shimming will more than accommodate your guns needs and make it sound great.
- With your specific set-up, I suggest using .03mm's of shims on the bottom of each gear as your baseline bottom gear height. This will flow with the already tolerance of the KWA gear teeth cut and mesh.
This is usually the correct height for the Sector Gear in Meshing properly with most Pistons in KWA Gearboxes using 5KU 9mm Solid Bushings specifically.
- After shimming the bottom of each gear, shim the top of each gear starting with the Sector and work your way to the Bevel Gear last.
When sticking to principles of shimming as a primary shimming method, I always start with the Sector Gear.
- The "play" tolerance on the top will be different for each gear.
KWA's tend to like it when you leave a bit of excess "play" in the gears vs shimming for perfection.
Also remember that when you close the Gearbox Shells and lock it down, it is much tighter than you think.
So, a tiny bit of excessive "play" will actually not hurt you.
I am sure you have noticed the tremendous amount of "play" with the 5KU 9mm Solid Bushings and KWA gears.
It is different world from the stock KWA 9mm Ball Bearing Bushings, which not only snap in the shell nice and secure, but come very close to a shimless gear set-up.
- The Spur gear is always tricky with KWA's.
I would start with one .01mm on the top and keep adding .01mm until you get it right.
You may find no shims are needed.
You may find a one or a few shims will work.
Rarely is it ever the same for me when shimming the top of this specific Gear in KWA guns.
- Bevel Gear.
1. This will be the gear that makes or brakes your build, both in terms of mechanical function and in terms of sound.
2. If the .03mm's of shims on the bottom does not seem just right, go with .04mm's of shims.
When you start adding more than that, you are getting into Bevel Pinion Method height which must be perfect or it just does not go well.
3. KWA Bevel gears are notoriously finicky when shimming the top face of them.
Less is more in this regard.
4. Just make sure you are patient and spend the time needed to get this gear shimmed correctly.
It will be the control that stabilizes the other two gears for it will be stabilized in place by the Pinion gear of the motor. It is a fine line between too much "play" and not enough with this gear.
Closing the Gearbox Shells:
This can be especially difficult with the 5KU 9mm Solid Bushings and KWA Gearbox Shells.
A few tips.
- Place the Bushings on the gears as you close the top half of the Gearbox Shells.
Do not try and place these Bushings in the Shell and expect them to stay in place as you try and close everything up. Even if you get lucky and the Bushing stay in place, you will have a difficult time lining up the Bushing holes with the gear shafts.
Better to place the Bushings on the gear shafts first, then use a tool such as a Pick to manipulate gear placement as you are working the Shells closed.
- Once closed, the Gearbox Shells may not feel flush or fully closed.
Use a Rubber Mallet to tap the Shells fully closed.
- Once everything is fully closed, use a tool such as that Rubber Mallet, or use a Hammer, and tap a Punch, Pick, or Screw Driver on every accessible gear shaft and Bushing.
I find that the 5KU Bushings fit and seat awkwardly even in the best of circumstances once the Gearbox Shells are fully closed. This step will loosen any awkward set placement and allow the Bushings to find their proper placement.
One last tip:
Use shims with small bandwidths.
Using large bandwidth shims on the Bevel gear can interfere specifically with the Spur Gear.
They can also interfere with the Sector Gear Cam that interacts with the Cut-Off Lever.
Also:
I don't know why this is, but when using 5KU 9mm Solid Bushings, I find that it takes a few seconds of the gearbox cycling with full power for the drivetrain to find its level plain of rotation.
So, if at the first trigger pull your gun is screeching, dry fire at least 300 rounds.
You may find that the sound of the gun goes from screeching to butter smooth.
Happy Airsofting.
I bet I know what gun this is.
If it is the one I am thinking of.....
- No matter what gun you shim, remember the bottom of the gears is for setting the height of the gears.
The top of the gears is for controlling the amount of Play.
- Make life easier on yourself.
Shimming KWA Gears paired with 5KU 9mm Solid Bushings is one of the most difficult shim jobs in all of airsoft.
It literally might be the toughest task of shimming out there, so don't be discouraged.
I can count on one hand at best the number of Techs in the USA that could pull it off using Bevel/Pinion Method and actually get it right, and no one at KWAUSA Inc. can even do it.
So, I do not recommend Bevel Pinion method unless you are already experienced with it and know what you are doing.
Make life easier on yourself. A shim job following the principles of shimming will more than accommodate your guns needs and make it sound great.
- With your specific set-up, I suggest using .03mm's of shims on the bottom of each gear as your baseline bottom gear height. This will flow with the already tolerance of the KWA gear teeth cut and mesh.
This is usually the correct height for the Sector Gear in Meshing properly with most Pistons in KWA Gearboxes using 5KU 9mm Solid Bushings specifically.
- After shimming the bottom of each gear, shim the top of each gear starting with the Sector and work your way to the Bevel Gear last.
When sticking to principles of shimming as a primary shimming method, I always start with the Sector Gear.
- The "play" tolerance on the top will be different for each gear.
KWA's tend to like it when you leave a bit of excess "play" in the gears vs shimming for perfection.
Also remember that when you close the Gearbox Shells and lock it down, it is much tighter than you think.
So, a tiny bit of excessive "play" will actually not hurt you.
I am sure you have noticed the tremendous amount of "play" with the 5KU 9mm Solid Bushings and KWA gears.
It is different world from the stock KWA 9mm Ball Bearing Bushings, which not only snap in the shell nice and secure, but come very close to a shimless gear set-up.
- The Spur gear is always tricky with KWA's.
I would start with one .01mm on the top and keep adding .01mm until you get it right.
You may find no shims are needed.
You may find a one or a few shims will work.
Rarely is it ever the same for me when shimming the top of this specific Gear in KWA guns.
- Bevel Gear.
1. This will be the gear that makes or brakes your build, both in terms of mechanical function and in terms of sound.
2. If the .03mm's of shims on the bottom does not seem just right, go with .04mm's of shims.
When you start adding more than that, you are getting into Bevel Pinion Method height which must be perfect or it just does not go well.
3. KWA Bevel gears are notoriously finicky when shimming the top face of them.
Less is more in this regard.
4. Just make sure you are patient and spend the time needed to get this gear shimmed correctly.
It will be the control that stabilizes the other two gears for it will be stabilized in place by the Pinion gear of the motor. It is a fine line between too much "play" and not enough with this gear.
Closing the Gearbox Shells:
This can be especially difficult with the 5KU 9mm Solid Bushings and KWA Gearbox Shells.
A few tips.
- Place the Bushings on the gears as you close the top half of the Gearbox Shells.
Do not try and place these Bushings in the Shell and expect them to stay in place as you try and close everything up. Even if you get lucky and the Bushing stay in place, you will have a difficult time lining up the Bushing holes with the gear shafts.
Better to place the Bushings on the gear shafts first, then use a tool such as a Pick to manipulate gear placement as you are working the Shells closed.
- Once closed, the Gearbox Shells may not feel flush or fully closed.
Use a Rubber Mallet to tap the Shells fully closed.
- Once everything is fully closed, use a tool such as that Rubber Mallet, or use a Hammer, and tap a Punch, Pick, or Screw Driver on every accessible gear shaft and Bushing.
I find that the 5KU Bushings fit and seat awkwardly even in the best of circumstances once the Gearbox Shells are fully closed. This step will loosen any awkward set placement and allow the Bushings to find their proper placement.
One last tip:
Use shims with small bandwidths.
Using large bandwidth shims on the Bevel gear can interfere specifically with the Spur Gear.
They can also interfere with the Sector Gear Cam that interacts with the Cut-Off Lever.
Also:
I don't know why this is, but when using 5KU 9mm Solid Bushings, I find that it takes a few seconds of the gearbox cycling with full power for the drivetrain to find its level plain of rotation.
So, if at the first trigger pull your gun is screeching, dry fire at least 300 rounds.
You may find that the sound of the gun goes from screeching to butter smooth.
Happy Airsofting.
-
captainkirk05
- I love forums!
- Posts: 251
- Joined: Sun Apr 08, 2012 12:35 pm
- Location: Greenville, SC
Re: Screeching gearbox
Yes Vanevery you guessed right, it's that gun. I wish I would have seen this post earlier before I tried to shim the gun. But all is good because I FINALLY got it right!
Most of the stuff you wrote I found out the hard way. I have literally spent 10 or more hours of my life trying to shim this gearbox right. A lot of that time is from putting the gearbox together to find I messed something up, and having to dive back in. I probably disassembled and reassembled the gearbox 7 or more times.
Yes, the shimming does get much tighter when the gearbox is screwed shut! I spent over an hour tinkering around and trying to close my gearbox before this realization slapped me like wet tuna.
Yes, those 5KU bushings are a headache. I had to slightly open the inner diameters of all of them with a dremel for the gear shafts to fit and move freely. On the other hand, they did snap into the gearbox shell holes quite nice. A few would fall out, but there was no play.
As for the measurements of the shims I use, if looking at the open gearbox with the nozzle to the right as is most common
Bevel gear: bottom 0.9mm : top 0.4mm
Spur gear : bottom 0.6mm : top 0.0mm no shims
Sector gear : bottom 0.6mm : top 0.3mm
The amount of play before the shims was surprising. After many tries and shim configurations, I feel I finally hit the money with this one. I actually went about prioritizing the bevel / pinion gear shimming, as this seemed to be the biggest issue in getting a smoothly working gearbox. My first shim attempt was based on meshing the spur to bevel first, and that was a mistake. If saying this makes me look like one of the few techs that can do the bevel / pinion shim method, trust me I'm not up there. It took me a chunk of failed attempts to finally get it right. And every time you mess up on that, it's at least another 30 minutes to readjust it.
As for using a rubber mallet to force the box closed, I would like to pitch in and say if anyone wants to try that, please make sure your wires haven't strayed out of place. You will be very unhappy if one has jumped to where the shell closes. I bit into my motor negative lead pretty bad and exposed some metal, but it still works fine. This was at a part of my project where I was getting extremely frustrated and impatient.
I can say my gun sounds silky smooth now. No gear screeching, just the faint whine any motor makes. The 1/4 inch of sorbo on top of the already installed KWA sorbo makes for a quiet impact sound as well. I got lucky with my first mosfet install too, no hiccups and does the job. The 9.6v 4200mah battery I was concerned about has turned out to be ample good enough for my build. Even with the SP150, the change to a mosfet and deans included, I get a crisp response (obviously not as fast as a large 11.1v, but good enough that I don't care).
My only concern now is compression. I had my hopup cranked up to pre SP150 spring settings, and about blew out my rhop patch and inner barrel 1/2 way out of the bucking. I was impressed at the force it must have taken to do this. But, I don't think it's quite where it should be. I have no chrono so that's my real problem. But I think I'm losing air somewhere in the system. The only quick fixes that come to mind is Teflon on the bucking (already did this), and spacers behind the hopup.
Most of the stuff you wrote I found out the hard way. I have literally spent 10 or more hours of my life trying to shim this gearbox right. A lot of that time is from putting the gearbox together to find I messed something up, and having to dive back in. I probably disassembled and reassembled the gearbox 7 or more times.
Yes, the shimming does get much tighter when the gearbox is screwed shut! I spent over an hour tinkering around and trying to close my gearbox before this realization slapped me like wet tuna.
Yes, those 5KU bushings are a headache. I had to slightly open the inner diameters of all of them with a dremel for the gear shafts to fit and move freely. On the other hand, they did snap into the gearbox shell holes quite nice. A few would fall out, but there was no play.
As for the measurements of the shims I use, if looking at the open gearbox with the nozzle to the right as is most common
Bevel gear: bottom 0.9mm : top 0.4mm
Spur gear : bottom 0.6mm : top 0.0mm no shims
Sector gear : bottom 0.6mm : top 0.3mm
The amount of play before the shims was surprising. After many tries and shim configurations, I feel I finally hit the money with this one. I actually went about prioritizing the bevel / pinion gear shimming, as this seemed to be the biggest issue in getting a smoothly working gearbox. My first shim attempt was based on meshing the spur to bevel first, and that was a mistake. If saying this makes me look like one of the few techs that can do the bevel / pinion shim method, trust me I'm not up there. It took me a chunk of failed attempts to finally get it right. And every time you mess up on that, it's at least another 30 minutes to readjust it.
As for using a rubber mallet to force the box closed, I would like to pitch in and say if anyone wants to try that, please make sure your wires haven't strayed out of place. You will be very unhappy if one has jumped to where the shell closes. I bit into my motor negative lead pretty bad and exposed some metal, but it still works fine. This was at a part of my project where I was getting extremely frustrated and impatient.
I can say my gun sounds silky smooth now. No gear screeching, just the faint whine any motor makes. The 1/4 inch of sorbo on top of the already installed KWA sorbo makes for a quiet impact sound as well. I got lucky with my first mosfet install too, no hiccups and does the job. The 9.6v 4200mah battery I was concerned about has turned out to be ample good enough for my build. Even with the SP150, the change to a mosfet and deans included, I get a crisp response (obviously not as fast as a large 11.1v, but good enough that I don't care).
My only concern now is compression. I had my hopup cranked up to pre SP150 spring settings, and about blew out my rhop patch and inner barrel 1/2 way out of the bucking. I was impressed at the force it must have taken to do this. But, I don't think it's quite where it should be. I have no chrono so that's my real problem. But I think I'm losing air somewhere in the system. The only quick fixes that come to mind is Teflon on the bucking (already did this), and spacers behind the hopup.
