specna arms edge 2.0 H20 - issues with shimming, bb curving left with hop and FPS.

[ThePilotWhoCantFly]

Sorry for the long post - please help!

Hi all, I bought my Specna Arms about 3 years ago and had a break from Airsoft for 2 years. I've recently gotten back into it and thought regreasing the internals would be a good idea, as well as upgrading some bits while at it. I have never opened an airsoft gearbox, but im pretty good with technical stuff in general. I decided to replace and install:
- 4UANTUM bucking and nub
- XT bushings CNC 8mm instead of the stock bearings
- SHS 13:1 gear set

I've got 3 issues.

1.) Shimming issue
2.) BBS curving left when hop applied
3.) FPS leak (I believe linked to issue 1, so I want to make sure it's not causing it)

For issue 1, I'm having an issue with the motor and pinion alignment. As many tutorials and people suggest, I used the half-shell method to align the motor and bevel gear (photo uploaded). I then shimmed it with both shells until there was just some slight play between the gears and shimmed the rest. All the gears spin freely together and have slight play between them. I proceeded to reassemble everything and test fire. The motor just spun and didn't engage with the gear. I then increased the height until it finally did and just used sound until the least noise/resistance was heard. I don't understand why the motor moves so much after reassembly to the point it can't even engage.

For issue 2, if I apply aggressive hop, the bbs start to curve left. And the accuracy of the grouping in general isn't great. I believe the issue is with the hop arm or the barrel window being miscut from the factory. I am unable to get the rubber bucking to protrude flat and centred to the barrel at the same time. I either rotate the barrel to get the bucking flat or centre the nub/bucking in the barrel, but it protrudes angled. Reference photos included. Im not sure if I just need to buy a new barrel and hop arm, or what will fix the issue.

For issue 3, my fps ain't great, especially with heavier bbs.
With hop applied, I am shooting:
0.32g at 200 FPS = 0.59 Joules
0.20g at 310 FPS = 0.89 Joules

With NO HOP, I am shooting
0.32g at 225fps = 0.75 Joules

I have tried re-shimming and trimming the tappet spring by 2 coils. Is it a normal amount of joules to be losing on .32s, or should they stay similar to 0.2s? Will a stronger spring fix my issue (It only came with the one installed)?
Thank you for reading!

 

[Colin Allen]

Your hop rubber appears to be off centre in the hop window; that will account for the curving flight. Set it up so that is central.

I am not sure what point you are trying to make with the motor and bevel gear; it seems that you have set it up properly if the gearbox sounds ok and the motor is not running too hot.

The power loss will not be linked to the shimming; it is more likely to be due to an air leak (piston head O ring, cylinder head O ring, nozzle/air tube interface, nozzle/hop unit interface) or the wrong cylinder, (Information on barrel/cylinder matching here: airsofttech.dk/Guides.cshtml?Page=CylBarVolRatio_Page1). Alternately, you might just have a very weak spring.

 

[Galvatron]

As a troubleshooting exercise, it's worth checking the seal in your cylinder by pushing the piston (with the head and O-ring) within the cylinder while you have a thumb over the nozzle. If you feel resistance and reach a point you can't push the piston all the way in, you've got a good air seal under compression so your spring may well be the culprit. If you get little to no resistance and are able to push the piston in all the way or you get resistance but are slowly able to push all the way down, there's an air leak of some sort due to one or a combination of the parts Colin mentioned.

 

[ThePilotWhoCantFly]

Your hop rubber appears to be off centre in the hop window; that will account for the curving flight. Set it up so that is central.

I am not sure what point you are trying to make with the motor and bevel gear; it seems that you have set it up properly if the gearbox sounds ok and the motor is not running too hot.

The power loss will not be linked to the shimming; it is more likely to be due to an air leak (piston head O ring, cylinder head O ring, nozzle/air tube interface, nozzle/hop unit interface) or the wrong cylinder, (Information on barrel/cylinder matching here: airsofttech.dk/Guides.cshtml?Page=CylBarVolRatio_Page1). Alternately, you might just have a very weak spring.

Click to shrink...

Thanks for replying!

So I uploaded 2 photos of the hop window. One them included the rubber being centered. In the photo you can seen the rubber that contacts the BB is angled. My groupings are pretty bad as well for some reason, I compared it to another specna H20 and it had much better and consistent grouping.

With the motor to bevel gear. I assemble it after adjusting it using the half shell method. I then try fire and the motor free spins. Even though with the half shell it was perfectly lined up as recommended. Some people suggested hat the motor might be somehow shifting after installing fully. I don't know what causing it and I just have to increase the motor height to get it to start engaging with the gear. I then increased it to the point I heard the least amount of noise which from what I've read online is not the proper way to do it.

All the listed components you mentioned are stock and I haven't messed with them apart from disassembly really. Honestly I don't even know if losing that many joules is normal when switch from .20 to .32s. Is it worth just getting a stronger spring and seeing what difference it makes? If so what spring should I get? I've got no idea what the stock spring is but it's a quick change system.

 

[ThePilotWhoCantFly]

As a troubleshooting exercise, it's worth checking the seal in your cylinder by pushing the piston (with the head and O-ring) within the cylinder while you have a thumb over the nozzle. If you feel resistance and reach a point you can't push the piston all the way in, you've got a good air seal under compression so your spring may well be the culprit. If you get little to no resistance and are able to push the piston in all the way or you get resistance but are slowly able to push all the way down, there's an air leak of some sort due to one or a combination of the parts Colin mentioned.

Click to shrink...

When I was reassembling I think I did this test and it performed well but I had to keep the piston around straight, if I angled it slightly it would cause an air leak to the side. It does just have 1 guide so I'm assuming when both sides of the shell are assembled it would be centered and there would be no issues.

 

[Galvatron]

When I was reassembling I think I did this test and it performed well but I had to keep the piston around straight, if I angled it slightly it would cause an air leak to the side. It does just have 1 guide so I'm assuming when both sides of the shell are assembled it would be centered and there would be no issues.

Click to shrink...

Yes, as long as your AoE is on point, the piston should remain centred.

 

[Adolf Hamster]

For the hop issue, assuming the stock hop unit is in good enough order as it was working previously there's a couple of options:
1. That the nub is actually square, i've had the off-brand omega style nubs be unsquare before and there's no easy fix other than buying one that is. Hence i always shelled for the proper maple leaf ones.

2. That the barrel is being held square in the bore, you can twiddle it a little left/right although it sounds like you've already got that covered.

Edit- internet nuked the second half of my ramblings somehow.

The air leak i'd start looking at nozzle-feedlips, seems the most likely candidate. Could be the bucking has short feedlips (reverting to stock would test that) or could be hop unit positioning, a spring or a stack of o rings around the inner barrel to push the hop against the gearbox is the typical fix for that.

As for shimming, i dont like starting at the bevel, you need to know high the sector+idler need to be for clearance that then dictates how much you can move the bevel up and down.

For setting motor height you always want to go from too tight then loosen, worst that'll happen is the motor stalls which as long as you dont dump power into it until it burns wont do any damage, whereas starting loose your pinion becomes a milling cutter that'll eat the bevel.

For testing shimming its best to strip the box of everything bar the gears and enough of the electrics to let you test fire. You want to be doing final testing with the shells bolted together as the compression from tightening it up can tip a zero clearance shimming into a negative clearance shimming. Its a pain in the ass but in a repetative and time consuming way rather than a strictly difficult way.

 

[Skara]

Your grip is most likely touching the receiver, which then throws off both the height and angle.
I suggest using grip spacers or sanding down the top part of the grip, so that when everything is assembled and tightened down there is still a very slight gap between receiver and grip.

 

[ak2m4]

For Issue 3 were you getting low fps before you changed the gears and hop rubber?

Very unlikely in the factory they didn't align the inner barrel hop rubber grove to the window but worth checking just in case. Quantum's do have a fairly smallish contact patch, if you have something like a MR lying around give that a try.

 

[ThePilotWhoCantFly]

For the hop issue, assuming the stock hop unit is in good enough order as it was working previously there's a couple of options:
1. That the nub is actually square, i've had the off-brand omega style nubs be unsquare before and there's no easy fix other than buying one that is. Hence i always shelled for the proper maple leaf ones.

2. That the barrel is being held square in the bore, you can twiddle it a little left/right although it sounds like you've already got that covered.

Edit- internet nuked the second half of my ramblings somehow.

The air leak i'd start looking at nozzle-feedlips, seems the most likely candidate. Could be the bucking has short feedlips (reverting to stock would test that) or could be hop unit positioning, a spring or a stack of o rings around the inner barrel to push the hop against the gearbox is the typical fix for that.

As for shimming, i dont like starting at the bevel, you need to know high the sector+idler need to be for clearance that then dictates how much you can move the bevel up and down.

For setting motor height you always want to go from too tight then loosen, worst that'll happen is the motor stalls which as long as you dont dump power into it until it burns wont do any damage, whereas starting loose your pinion becomes a milling cutter that'll eat the bevel.

For testing shimming its best to strip the box of everything bar the gears and enough of the electrics to let you test fire. You want to be doing final testing with the shells bolted together as the compression from tightening it up can tip a zero clearance shimming into a negative clearance shimming. Its a pain in the ass but in a repetative and time consuming way rather than a strictly difficult way.

Click to shrink...

So the bullets curving left I believe happened from when I bought it. It was my first Airsoft gun so I just kinda of thought that it's normal for an Airsoft gun to be inaccurate. The hop arm has been glued together from 2 separate pieces and are slightly missaligned but I dont know if that's what's causing the issue.

Everyone recommended 4uantam to me, is it worth getting a maple leaf then? What degree do you recommend?

Do you mean is the rifle sitting square to the hop unit chamber? It is but as mentioned and shown in the photos it causes the nub to expose at a slight angle.

So I think I found the are of the FPS leak. To test the piston compression I always did it without the air nozzle?(The nozzle that's connected to the tapet plate). I only had the front plate of the cylinder with that nozzle and the compression was fine. I just assembled it and tried it with the air nozzle installed and I can fully compress the piston and there's an air leak. Im assuming that's not normal behaviour? I've applied silicone oil to the inside o rings of that air nozzle but it seems to not have helped.

For shimming I'm kinda of limited by the bevel gear as I can't go higher or lower than 0.2mm of shim(on the RHS/flat face of the bevel gear). Any more and there's is almost no play between the motor and gear. Any less and the gear starts to rub against the housing as I have low profile bushings installed.

Either way I'm happy with how I've shimmed it. With all the housing bolts and gears installed they all spin freely with no resistance.

 

[ThePilotWhoCantFly]

Your grip is most likely touching the receiver, which then throws off both the height and angle.
I suggest using grip spacers or sanding down the top part of the grip, so that when everything is assembled and tightened down there is still a very slight gap between receiver and grip.

Click to shrink...

I'll have a look when I've reassembled everything. So if there is no gap between the receiver and grip you suggest sanding it down?

 

[ThePilotWhoCantFly]

For Issue 3 were you getting low fps before you changed the gears and hop rubber?

Very unlikely in the factory they didn't align the inner barrel hop rubber grove to the window but worth checking just in case. Quantum's do have a fairly smallish contact patch, if you have something like a MR lying around give that a try.

Click to shrink...

Honestly I'm not sure. Since I was new I didn't have a chrono and was never able to test what FPS I was getting in heavier weights. At the Airsoft sight I went to they chronod on 0.2s and I got around 320-330fps if I remember correctly. Currently I get 310fps on 0.2s and my joules decrease on heavier bbs. From what I've read online joules should stay the same and it could increase potentially sometimes via joule creep.

If you look 2 comments above though I think I figured out the cause of the FPS issue. I always tested piston compression without the air nozzle (the thing that's attached to the tappet). Without it I can't compress the piston fully and it holds pressure. I've added the nozzle and I can compress the nozzle. I've added silicone oil to the o ring in the air nozzle but it still doesn't hold pressure. This is all stock.

Im honestly not sure what's causing the BB curvature to the left. Like I've shown in the 2 comparison images I cant get the angle of the bucking to be flat and centered within the barrel. That's why I think the barrel window has been cut incorrectly and off centered. I've seen that you don't have any barrels available on your store currently. I need a 275mm barrel and I found a 6.02mm maple leaf barrel for £20. I asked on the Airsoft discord and they said its not a good barrel and recommend a lambda 01/03 but it's around £50 including postage. Any recommendations?

 

[Colin Allen]

So the bullets curving left I believe happened from when I bought it. It was my first Airsoft gun so I just kinda of thought that it's normal for an Airsoft gun to be inaccurate. The hop arm has been glued together from 2 separate pieces and are slightly missaligned but I dont know if that's what's causing the issue.

Everyone recommended 4uantam to me, is it worth getting a maple leaf then? What degree do you recommend?

Click to shrink...

A Maple Leaf Macaron or MR yellow rubber; remember to get an Omega nub as well; AK2M4 usually have them in stock and delivery very quickly.

Do you mean is the rifle sitting square to the hop unit chamber? It is but as mentioned and shown in the photos it causes the nub to expose at a slight angle.

So I think I found the are of the FPS leak. To test the piston compression I always did it without the air nozzle?(The nozzle that's connected to the tapet plate). I only had the front plate of the cylinder with that nozzle and the compression was fine. I just assembled it and tried it with the air nozzle installed and I can fully compress the piston and there's an air leak. Im assuming that's not normal behaviour? I've applied silicone oil to the inside o rings of that air nozzle but it seems to not have helped.

Click to shrink...

It seems that there is too much tolerance between the nozzle and the air pipe. Measure the length with vernier callipers and buy a metal nozzle of the same length with an O ring; again, AK2M4 usually have a good choice. A different cylinder head may also be needed, depending on which is off spec

You don't want silicone oil anywhere near the nozzle; it will get onto the hop rubber and reduce the effectiveness of the hop.

For shimming I'm kinda of limited by the bevel gear as I can't go higher or lower than 0.2mm of shim(on the RHS/flat face of the bevel gear). Any more and theirs is almost no play between the motor and gear. Any less and the gear starts to rub against the housing as I have low profile bushings installed.

Either way I'm happy with how I've shimmed it. With all the housing bolts and gears installed they all spin freely with no resistance.

Click to shrink...

One thing to check is that the tappet plate tail and fin is not held too tightly between the sector gear and the side of the gearbox. If you have shimmed the gears too high that can be a problem.

 

[ThePilotWhoCantFly]

A Maple Leaf Macaron or MR yellow rubber; remember to get an Omega nub as well; AK2M4 usually have them in stock and delivery very quickly.

Many stock nozzles leak as they do not have an internal O ring. Measure the length with vernier callipers and buy a metal nozzle of the same length with an O ring; again, AK2M4 usually have a good choice.

One thing to check is that the tappet plate tail and fin is not held too tightly between the sector gear and the side of the gearbox. If you have shimmed the gears too high that can be a problem.

Click to shrink...

I'll have a look at ordering the bucking then and see if that'll fix my issue. But I do kinda think that the barrels window has been miscut.

The cylinder and nozzle is all metal and the nozzle does have o rings inside. Edge 2.0 comes with some "upgraded" internals including those metal components. Is it normal for the air nozzle to slightly wiggle around while attached to the tapet plate? Is it just worth putting some teflon tape on the cylinders nozzle?

I'll double check when I reopen the gearbox. I know I have 0.8mm of shim on the sector gears tapet side, if that means anything to you.

 

[Colin Allen]

I'll have a look at ordering the bucking then and see if that'll fix my issue. But I do kinda think that the barrels window has been miscut.

The cylinder and nozzle is all metal and the nozzle does have o rings inside. Edge 2.0 comes with some "upgraded" internals including those metal components. Is it normal for the air nozzle to slightly wiggle around while attached to the tapet plate? Is it just worth putting some teflon tape on the cylinders nozzle?

I'll double check when I reopen the gearbox. I know I have 0.8mm of shim on the sector gears tapet side, if that means anything to you.

Click to shrink...

Many stock airsoft barrels are not great.

The nozzle should not really "wiggle" on the tappet plate; it should fit snugly. You might need a new tappet plate and/or cylinder head. Teflon tape will just get destroyed and end up where it shouldn't be.

If you reassemble the gearbox without the piston and cylinder, you can see how much space the tappet plate has.

Good luck!