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Ics Split Gearbox Tappet Plate Issue


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I recently picked up a used ICS M16 (Thanks again, Psycho). As I was fully aware at the time of purchase, the gun was non-functioning. The primary reason for this was a stripped spur gear. Due to this, I decided to make multiple inexpensive upgrades while replacing the gears. Unfortunately, after I had the rifle fully assembled, the tappet plate would not properly cycle. It appears as if the tappet plate will start in the forward position (fully seated into the hop-up unit), but after the first shot the nozzle will not return to this position. My first thought was that the tappet was binding between the sector gear and the gearbox shell; however, when i close the gearbox (before firing it) i'm able to easily push the nozzle in and the spring easily pushes it back out. Additionally, it seems like every time I open the rifle, the gears are facing up which is pulling back the tappet plate. My first thought was that I was dealing with over-spin; however, that seems highly unlikely on such a strong spring with a stock motor. I've scoured the internet and I have not been able to find this specific issue. My part list is below.

 

Gears: ZCI 13:1

Motor: ICS 3000

Mosfet: Nukefet

Battery: 3000mah 7.4V (20C) (also tried 1000 mah 11.1v 20C)

Spring: Guarder M120 (also tried stock spring)

Cut-Off Lever: Stock (I assume)

ARL: ICS (stock)

Tappet Plate: SHS V2

Nozzel: SHS AK (long)

Cylinder Head: SHS V2

 

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Take the spring/piston out and then assemble the gearbox. Rotate the gears in small increments and see at what point the tappet plate gets stuck

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Take the spring/piston out and then assemble the gearbox. Rotate the gears in small increments and see at what point the tappet plate gets stuck

 

I did that to some degree with half of the upper and the spring/spring guide taken out so that I could see if the tappet plate was getting stuck. it should have plenty of room to move freely once the gear rotates. 

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NebAnon

I have a similar issue with my ICS split gearbox, although it may differ because my issue was prompted by a broken hopup feed tube and then subsequent replacements were not working properly. But I think the tappet plate was giving us issues at some point as well. We tried all manner of trouble shooting; using different uppers, re greasing, and using a variety of pieces interchanged, etc. I can't remember each specific result we achieved, but none were satisfactory. TP can also chime in on this as he was my main source of help. The whole experience with it has been.....character building... I guess? I'm sorry I am not much help, but after dicking with it for awhile, some real life events kinda took precedence and it has been back-burnered for the moment. Please update when you do end up finding a solution though, as I really loved my little ICS and want to get it fixed. 

Edited by NebAnon
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Hanback

I am willing to bet that your sector gear is shimmed too high. Although there is difference in the ICS split design vs standard, it is still possible and your problem description exactly matches that of a binding tappet. Take appart the lower and make sure to shim the spur and sector as low as possible. Refer the the pinned topic at the top of this forum section for specifics on this.

 

This issue is never directly apparent because the gearbox shell has to be fully torqued down for the issue to arise, making troubleshooting difficult. Hopefully it solves the issue.

 

Also, without installing the hop up,close the gun and watch it cycle. Does the nozzle move as desired? If so, then the issue will be between the hop-up and gearbox joint. If not, then it is all internal.

 

*Edit*

Also, possibly a dumb point, but ensure that your gears are held in place properly with no side to side play. Play in the gears (namely sector) can allow them to bind after initial cycle and if it is partially recycling, then the force of the spring on the system won't let it gently unbind to release the tappet. I assume you shimmed it all nice and snug (not tight) but it is a reality check. Been there done that myself, live and learn.

Edited by Hanback
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I am willing to bet that your sector gear is shimmed too high. Although there is difference in the ICS split design vs standard, it is still possible and your problem description exactly matches that of a binding tappet. Take appart the lower and make sure to shim the spur and sector as low as possible. Refer the the pinned topic at the top of this forum section for specifics on this.

 

This issue is never directly apparent because the gearbox shell has to be fully torqued down for the issue to arise, making troubleshooting difficult. Hopefully it solves the issue.

 

Also, without installing the hop up,close the gun and watch it cycle. Does the nozzle move as desired? If so, then the issue will be between the hop-up and gearbox joint. If not, then it is all internal.

 

Thank you for this. Nox actually suggested a similar route to me when I first found the issue, but I thought that since I could freely compress and retract the nozzle before firing it while the gearbox was fully assembled, the tappet had free reign to move between the shell and the sector gear.  I believe I only have a .1 under the spur gear so i'm very limited on my ability to lower the sector gear. Would shaving down the "hook" on the tappet plate have a similar effect? 

Edited by Rex
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Hanback

Thank you for this. Nox actually suggested a similar route to me when I first found the issue, but I thought that since I could freely compress and retract the nozzle before firing it while the gearbox was fully assembled, the tappet had free reign to move between the shell and the sector gear. I will try reshimming (although I believe I only have a .1 under the spur gear so i may have to sacrifice sound quality to lower the spur and therefore the sector. ha.

Even if only for a few cycles, the sanity check to make sure the gears aren't too high can be enough to rule out this as the potential issue. Prolonged use with rubbing on the shell is not good, but you'll be fine for a handful of cycles.

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What would you think about shaving the tappet plate to reduce binding between the sector gear and shell? I'd hate to butcher a new tappet plate needlessly but it is only $4...

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Hanback

It's an option, but a last resort. As soon as you start removing material, you begin to weaken it which reduces it's lifespan of use. Granted I have only ever seen a few tappets truly ever fail, it is still a possibility. If it solves the issue though, then it's viable, just keep a spare on hand in case it breaks.

 

Again though, try and diagnose and repair it every other way first. Sometimes, the most aggravating and unsolvable issues are simple, stupid, overlooked things. I think every gun tech can echo that sentiment from at least once in their life.

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Sometimes, the most aggravating and unsolvable issues are simple, stupid, overlooked things. I think every gun tech can echo that sentiment from at least once in their life.

 

Once spent an unspeakable amount of time trying to get a trigger to fit correctly inside the gearbox so that it would operate correctly. Come to realize that it was just hitting the cut off lever and resetting itself :lol:

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NebAnon

I tried shaving down the tappet plate and it did not help. Also, the gearbox was designed around a proper tappet plate, so even if shaving it down did work, its just a bandaid to an underlying problem else where. And when it comes to gearboxes, an underlying problem now with a bandaid will be a hemorrhagic disaster later.

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Well, I may have identified the issue. Nox suggested that I try firing without the hop up in. The nozzle functioned just fine! I thought that since the nozzle "fit' into the hop up that couldn't be the issue. It apparently when the upper and lower are. Loses together the nozzel was getting snagged. I'm hopeful that changing the nozzle back to stock will fix the issue, but I will once again be left without an o-ring nozzle.

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Hanback

Well, I may have identified the issue. Nox suggested that I try firing without the hop up in. The nozzle functioned just fine! I thought that since the nozzle "fit' into the hop up that couldn't be the issue. It apparently when the upper and lower are. Loses together the nozzel was getting snagged. I'm hopeful that changing the nozzle back to stock will fix the issue, but I will once again be left without an o-ring nozzle.

Only a handful of guns I have ever produced have an O-ring sealed nozzle that is properly functioning. In engineering terms of efficiency, without yields lower efficiency which means you aren't squeezing as much potential out of the gun as possible.

 

In reality, the difference isn't noticeable. If anything, it can help maybe 1-3 fps, but even the best tuned setups have fluctuations (i.e. chronos between x and y fps) and although lessening the fluctuations are desired, it's not actually possible as it depends on factors well out of you control; like temperature, ambient pressure, humidity, so on.

 

In simple terms, a non O-ring sealed nozzle will be fine. The difference is negligable and provided everything else compression wise is good and set right, you shouldn't see a difference in fps/efficiency when shooting the gun.

 

This is assuming that the nozzle is in good condition that is though. Hope it helps.

Edited by Hanback
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I'm surprised that I'm having the nozzle issue, especially since it's a Madbul hop-up and the nozzel fits when I initially place the upper gearbox into the upper receiver and close the receiver. My guess is that I could sand the portion of the hop up where the nozzle enters and it would work fine but before I try that I'm going to switch back to the stock nozzle.

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UPDATE: I have ruled out both the nozzle and tappet plate as being the culprit. This likely leaves me with needing to install an OEM hop-up unit; however, before I do that i'm checking with the previous owner to determine if the ICS previously functioned with the Madbul hop up. If it did, i'm back to trouble shooting. If it didn't then i'll hopefully be able to address the issue with a $20 part. My current theory is that the Madbul hop up unit becomes pinched in some way when the receiver closes which causes significant friction/pressure between the hop up and nozzle. That would explain how the nozzle fits into the hop up when the shell is initially closed but doesn't return after firing the first round. The nozzle does not appear to go any further into the rifle than the half way point where the ridge is located. 

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hrturner

Noticed you mentioned the unit had a fet. Fets tend to be more efficient at turning on and turning off electricity. The traditional blade-trigger system usually has a ramp up which can lead to the motor slowly spinning up. I've seen instances where replacing blade-trigger systems with fets has caused similar motor over-spin issues. Is your fet programmable? Sometimes they have settings that can be tuned per gun to offset the now instantaneous rush of electricity when the trigger is pulled. 

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  • 3 years later...

Rex, hopefully you're still active on this site. I am having this exact same problem, and I'm hoping you found a solution to yours. Just bought a new ICS CXP MMR Carbine, and I left it sitting there untested for months. Finally got around to shooting it, and it doesn't work. After extensive troubleshooting, I got the idea to shave off the trigger trolley spring guides on the bottom of the tappet, and it's just barely sticking still.

Did you ever find a solution?

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