My First Time Opening a Gearbox (VFC avalon gen 2)

Discussion in 'Gun Building, Modifications & Repairs' started by Evan J Johnston, Jun 8, 2020.

  1. Evan J Johnston

    Evan J Johnston Member

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    Got around to taking a look at the RIF today. Piston was all the way forward before I touched the GB, but the tappet plate wasn't. It sprung forward as I was pulling the shell apart, and I noticed the trigger trolley spring was mounted such that it was interfering with the tappet plate. I really hope this is the reason for the low FPS. I believe it's also possible this caused the trolley to be held ajar. Electrical components all check out. Did a quick test after disassembly and motor spins fine. Motor heats up a bit, but seems to stabilize at a reasonable temperature. I did like 30+ successive trigger pulls with the motor in my hand. I will reassemble and test tomorrow.
    I do have some more pictures and a video to show some concerns, though:
    I have an intermittent airseal issue ONLY when the tappet plate is installed. Everything else checked out fine. I noticed the Lonex tappet doesn't sit perfectly flat against the front of the gearbox, whereas the VFC does. The Lonex tappet also doesn't quite hug the nozzle as well as the VFC tappet plate. This is very hard to see in the pictures but if you look closely I think you can see that there's more of a gap between the nozzle and the Lonex tappet at the bottom. The nozzle is definitely held more securely by the VFC tappet. I'm considering modifying it to fit the Lonex GB.
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    Here's the video showing the intermittent airseal issue. It seems to be quite literally fractions of a millimeter difference in the way the tappet sits that affects the airseal. I cannot visibly tell the difference. I just have to fiddle with it a bit to make the change.
     
  2. Evan J Johnston

    Evan J Johnston Member

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    In its most recent state, my unit was definitely passing the tests presented in your video. Thanks for that, btw. It was with the sector gear installed that problems start showing up. the COL sticks just a hair too high, but I've nearly corrected this by using a damaged trolley and the new contact unit that fits better onto the peg in the GB with the replaced MOSFET. In testing, the COL has gouged the part of the trolley's lip that it engages with to the point where it now works lol. It's ugly, but it works. I'm a little uncertain of how this will hold up and I got tired of dealing with it, so I ordered an Airsoft Systems ASCU trigger unit (Gen 4). Its a MOSFET and microswitch with its own special mechanical cut off lever that flips a switch in a manner that looks much less finnicky. I'm running low on funds and was not willing to go into the optical ETU MOSFET realm. I felt those systems can be quite fragile, relying on being held in place with only one screw. I was having visions of the unit jiggling in the gearbox and causing unintentional discharge, or getting wet or something and being out $150.
     
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  3. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

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    Compression Tests of the Cylinder does not require the Nozzle to be installed.

    The Physical Properties of Fluid Dynamics proves that the part that is important is only the cylinder head, cylinder and piston with piston head. Air takes the path of LEAST resistance. Air will NOT move down and back in a system that is an "open" system which is what an AEG is operating under.

    Your finger on the Nozzle makes this a CLOSED system...which renders your test in the OPEN system...flawed and irrelevant and causing you more work than is really necessary.

    Another Airsoft Myth has been created with O-Ring Nozzle and thinking that the nozzle on the cylinder tube is required for a compression test.
     
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  4. aotsukisho

    aotsukisho Active Member

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    While it's true there can be mechanical clearance issues (sector gear, trigger) that lead to damage, I think it's highly unlikely. Sensible greasing, and not dunking your AEG in water or playing in rain will mitigate liquid-based damage as I think majority of us all do with any AEG. The screw is mainly there to lock in X-Y axis movement, the top portion of the Titan has a compression fit with foam to the top of the gearbox to prevent Z-axis movement, I have never had issues with mine moving around while in use. The wires are also extremely stiff and I would assume help with keeping the ETU itself immobile in the shell.

    Frustrating problems. The cutoff lever is the biggest problem in my opinion with airsoft gearbox designs and I'm glad the computerized systems these days are mitigating how essential it is for operation. It's way too sensitive and sometimes temperamental for how important it is.
     
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  5. -Spitfire-

    -Spitfire- Well-Known Member Supporting Member

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    Ummm. Except that I've already demonstrated on multiple AEGs that this isn't the case. One of the issues with your supposition is that when it fires, the BB causes resistance as long as it's in the barrel (which is why I'd argue that it's a closed system, but that's less relevant). This resistance is pretty shortlived, but it's there nonetheless. This is lessened in systems with properly fitted nozzles(honestly, not aware of any companies that fall in this category other than TM), but is still present.
     
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  6. Evan J Johnston

    Evan J Johnston Member

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    Gotcha. Very good to know.
    I finally got the bad lad running nicely tonight.
    I noticed the nozzle was stuck in the retracted position, so that pointed me to looking into the tappet plate. I assembled the gearbox with everything except the cylinder, CH, and nozzle and found that the tappet plate would NOT budge at all. I ended up shaving both sides of the tappet plate down with a dremel and smoothing with sandpaper, then washing with water and drying it thoroughly for each test. I think I took off a full millimeter on each side. The lonex tappet plate has a section cut out at the front to fit into the Lonex gearbox, which has some reinforcement in this area, so its a bit thicker. I ended up having to shave down both sides of the tappet plate to match this. I got my Lonex GB from evike, if that matters. I know Guges has poor things to say about evike and theyre issues with G&P products in the past. I'm not impressed that I had to do this, when Lonex GB comes with its own tappet plate to match the changes. Of course quality control is never perfect in the airsoft world, but still.
    All firing modes work as they should and I'm getting ~370 FPS with a .2g on a madbull m100 spring. The Lonex SP100 yielded ~412 FPS on .2g, 351 on .25g. Is it true that the M[x] rating is supposed to be [x] m/s with .2, and SP[x] is supposed to be approx. [x] m/s with .25?
    It's now past 5am here, so I'm heading to bed. I will update this post later with a recap of what I've done with this RIF, a few pointers, and maybe some more photos and sources I referenced while working on this thing. I'm not certain if my semi-auto will continue to function well, so I will definitely be putting in the Airsoft Systems ASCU gen 4 that I ordered from evike. It probably won't be here until late next week.
    Thanks so much for the guidance guys I really appreciate having people here to lend suggestions. I've learned quite a bit from this experience, and I intend to continue learning. My hope is to gain enough knowledge and experience so that I can do tech work as a side gig while I'm at college and get an airsoft tech YouTube channel going. I'll be transferring to the University of Wisconsin-Milwaukee Engineering School for Spring 2021.
     
    Last edited: Jun 30, 2020
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  7. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

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    Spitfire I respect you, but physics is against you.

    I have been undertaking another project that is dealing with Air Flow and I am learning quite a lot.

    There are three other guys here that have verified that it has no effect. Plus the House of Krytac and Tokyo Marui states...there is no benefit to o-ring nozzles.

    Fluid Dynamics is on our side. What I noted before is that in some badly made AEGs it helps nozzle alignment or tolerances between air nozzle and cylinder tube. That is where Fluid Dynamics will support you because it centers the flow (turbulence reduction is key) and improves FPS.

    This ties into my current project where we are moving Air via a DC fan and our coil ducts slow down air movement. This is due to the fact that we are inducing turbulence into the air way. When we had ducting going straight...air was passing in and out of our chamber in two seconds. So we put in baffles and coil ducting to disrupt the air flow. Now we are up to 8 seconds. Travel path is still 18" but the turbulence is a major factor in reducing pressure.

    So, in Airsoft when a nozzle is properly made and fitted to the cylinder Air tube...an o-ring that takes up the .25mm gap is not needed. Now if tolerances were really loose and the nozzle was off kilter. The o-ring will assist in alignment and helping air flow, which leads to an increase in FPS.

    Now I will agree there is a minuscule amount of "backflow"...but time of contact to bb movement is less than .03 seconds in a 15 RPS AEG.
     
    Last edited: Jul 1, 2020
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  8. Evan J Johnston

    Evan J Johnston Member

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    Well then, since that's settled, here's the summary of the effective job completed on my VFC Avalon MK18 as I understand it (not in any particular order):

    Problem: Broken spur gear tooth
    Solution: Replace with SHS 16:1 (stock ratio) CNC steel gears, and shim
    Observations: This gear broke VERY soon in the gun's life, perhaps a lemon. I accidentally messed with motor height before I knew what I was doing. The top of bevel gear was scraping on the inside of the GB shell at some point. No other evidence to suggest fatal motor height issue.

    Problem
    : Trigger locking up on semi-auto, feels as if on safe. This problem was present since brand new OOTB. Eventually progressed to firing full-auto in semi.
    Solution: New, higher quality trigger switch assembly. Unknown brand. Black in color, unknown material, good quality casting/machining. Labeled SHS from my local shop, but I've only seen red V2 units from SHS and they look of lower quality than this one. To maintain the original VFC MOSFET, I de-soldered everything from it, unscrewed the plate holding the trigger contacts in the unit, then carefully separated the MOSFET from the contact assembly with a small flathead screwdriver. Once removed, I VERY CAREFULLY sanded off the old, dried superglue*, placed the trigger contact unit in the gearbox, and got an idea of how I wanted the MOSFET to sit. I put the small body pin in place that would normally be there once the gun is fully assembled. I then proceeded to apply super glue quite sparingly, spreading it around the contact assembly surface without getting too close to the edges in order to avoid squeezing it out into places I didn't want the glue, then pressed the MOSFET into place and held it there with good, even force for about 2 minutes. Re-soldered it back together. Good as new.
    Observations: It would be a very good idea to take pictures of anything wiring related to be sure you put everything back the way it should go.
    *Be VERY careful when doing this, as you may sand away silicon and expose the leads in the PCB. Not good. If you mess this up, you could still cover it with super glue, but you may have added some resistance to the circuit if you removed any of the electrical lead.

    Here's a secondary part of the job that was due to my own errors and/or having used a different gearbox shell:

    Problem: Broken screw stuck inside VFC "ECS" Gearbox shell
    Solution: Replaced with Lonex Gearbox shell -- 8mm ball bearings and proprietary tappet plate included. Failed to extract screw from VFC shell.
    Observations: VFC cylinder has a tough time fitting in the Lonex shell, as does the trigger contact unit. You really have to muscle these pieces in there for them to work. I do not recommend using these trigger contacts in this scenario. I suspect if I went with another VFC gearbox, there would have been significantly less headache with this job. VFC seems to like not doing things to Tokyo Marui spec, or perhaps their tolerances/QC are ****, or my particular unit just happened to get the **** end of the tolerances on a bunch of parts. It's truly a mystery to me. I wish I had just gotten a complete Lonex gearbox, or a VFC ECS shell.

    Problem
    : Low FPS (~150 FPS on Lonex SP100 spring with either .2g or .28g BBs -- got mixed up in testing) -- nozzle not moving during test fire, unable to be pushed back or pulled forward.
    Solution: Used a Dremel to cut down the sides of the tappet until it had enough space to move the way it should. I ended up removing about 1mm on each side, nearly flush with the recessed portion of the tappet plate that Lonex cuts out in order to fit around the extra reinforcing material inside their gearboxes.
    Observations: Very strange to me that this tappet plate did not glide freely in the gearbox it was designed to work in. In fact, it didn't move at all when assembled, it would get pulled back by the sector gear, then stay seized in place by the gearbox.

    Problem: Feeding issue
    Solution: WIP
    Observations: Initially, it was feeding ~8/10 shots at the beginning of my latest game day (Sunday, June 28), by the end it only fed ~1/2, sometimes double feeding.
     
  9. Evan J Johnston

    Evan J Johnston Member

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    Added a picture of the RIF fully assembled and quoted the summary reply in the OP.
     
  10. Evan J Johnston

    Evan J Johnston Member

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    I've encountered some serious feeding issues. I got to play a private event on Sunday. Initially, it was feeding ~8/10 shots at the beginning of the day. By the end it only fed ~1/2, sometimes double feeding. I'll be doing some research on this in the mean time, but have to focus on school, etc.
     
  11. LittleTech

    LittleTech New Member

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    Hey man, you say you grinded the hole to get the gearbox fit right? Did it work well? My dsg is optical sensor so I’ve been debating to open the hole or just keep the duct tape over the hole.
     
  12. Evan J Johnston

    Evan J Johnston Member

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    PM'd
     
  13. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

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    Could be a tear that was slowly developing in the hop-up packing/rubber
     
  14. Evan J Johnston

    Evan J Johnston Member

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    no tears. I was using a brand new G&G green. swapped for maple leaf super macaron yellow (60 degree). same results. The lonex gearbox doesn't exactly fit perfectly in the body. I had to grind down some parts to fit it in the lower already. It scrapes pretty hard along the inside bottom edge of the upper and the charging handle also binds up a bit on the top of the GB. I thought this might be negligible as long as everything can be put together. The upper appears to get pushed up a bit. Looking closely at the gaps between upper and lower, the gap appears to grow towards the front. It is visible on both sides, but more pronounced on the bolt release side of the body. The front pin just before the handguard also looks to be deflected in a similar manner. Could this be affecting the function of the nozzle or alignment with the hop unit/barrel? I saw a video where a dude ground down the front piece of his tappet plate that holds the nozzle so that it could bend more to allow the nozzle to shift more to compensate for issues with alignment. According to him he spent a lot of time developing that fix and he seems pretty confident it is effective in at least some instances. What do you think I should try first? My hunch is that this tappet mod should be kind of a last resort, but could potentially be easier to do than hunt down parts of the gearbox that are interfering with the body.
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    Last edited: Jul 1, 2020
  15. aotsukisho

    aotsukisho Active Member

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    I'd recommend fixing the alignment rather than trying a fix that doesn't solve the underlying issue.

    The grip looks tight on the replica, you should probably triple check to make sure that tightening down the grip doesn't alter the alignment due to how it fits in the body/gearbox. Shave down the motor grip where it contacts the lower receiver, ideally you want a barely visible space between the two.
     
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  16. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

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    MB alignment...bend the tappet is going to cause pressure deflection (turbulence) and that will lower FPS.
     
  17. Evan J Johnston

    Evan J Johnston Member

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    Hah funny you mention that I actually did shave down parts of the grip when I originally was trying to get the gearbox fitted to the lower to make sure it was flat against the mounting surface but I didn't really check how it affects the body. Thank you for the tip.

    Gotcha thanks for the heads up.
     
  18. Guges Mk3

    Guges Mk3 Well-Known Member Supporting Member Lifetime Supporter

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    And this whole scenario is what has happened in the industry.

    Back 16 years ago. Parts were 85% compatible and you can just mix and match with a bit of filing.

    With the lack of standards it has become the opposite of 85% incompatibility now days.

    With the lackadaisical assumptions that get propagated through the internet that you can "just" buy a part and put it in"...has lead to many of us going bald...
     
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  19. Evan J Johnston

    Evan J Johnston Member

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    *Big sadface*
    Yeah I'm putting this gun on the back burner sort of. Gonna just slow down and take my time with it. Just ordered $100 in parts from brill and a CYMA Platinum M4. Gonna go play with the cyma while I tune the living **** out of this VFC/Lonex monstrosity. It's truly a beautiful RIF externally. Wish I had Colt trades. Maybe I'll try drilling and re-tapping the threads on the original VFC gearbox before I go modifying everything else.
    Guges do you know the actual OEM of the cyma platinum series? I think you or someone else mentioned in another thread that it isn't made by cyma since they only OEM AKs, right?
     
    Last edited: Jul 2, 2020
  20. -Spitfire-

    -Spitfire- Well-Known Member Supporting Member

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    Cyma OEMs more than just AKs (I can't speak for the platinum series though).

    Personally, I'd just rethread the original shell. It'll be easier in the long run.
     
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