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Gunmane

Gunmane's Gearbox Woes

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Spent most of the weekend trying to tackle this accursed gearbox for my rpk.  The new wire harness set had one of the contacts break so after getting the old set back in to at least have it function again I run into more problems.  *suitcase* phone imagery ahoy!

https://i.imgur.com/AU6BAZA.mp4

Forward/Safe position:

EcPeUPb.jpg

What would be semi:

eDjLjfm.jpg

In the safe and full auto position the motor gets power; in the semi auto position I get nothing but the ever familiar click.  Now, if I push the selector plate past what the selector gears would push it, the plate pushes up against the cutoff lever nub and lifts it back up again and the motor would receive power.

Motor height is fine, sector gear is engaging with the cutoff lever, trolley is making regular contact, everything seems fine every time for the past two days I have taken it apart and put it back together.  Earlier I even looked at it with the piston assembly out and found that as long as the motor height was just right it would fire semi fine but if a bit low the cutoff lever would get stuck at some point until I moved the selector plate back into safe/full auto position.

I'm at a loss, my hands are cut up to hell, and I am down my rpk for one of the last games of the year.

 

Edit:  After two more attempts, I have managed to get it to function in semi, but I have doubts it will stay that way by the time I get it back in the gearbox.  I will probably keep this thread around for future gearbox rants if permitted.

Edit:  Put it into body, pull semi a few times, all good, shift to auto, to safe, then back to semi, back to square one again.  *fruitcage* LCT.

Edited by Gunmane
update again

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Not being funny, but have you actually function tested this with the gearbox fully assembled? As in, motor cage connected etc.

Because if you've assembled the gearbox with the sector gear only just engaging the cut off lever, it can lift the COL into a position which will stop the trigger contacts from making contact properly - this is the cause of the dreaded 'lock up in semi' issue. If you've got the gearbox full assembled, a quick blast of full auto will bypass the COL and your semi auto should work fine as it will have 'reset'.

Now, if you're still getting the semi lock up problem when it's all put together, then that's a more serious concern.

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Yes, I have multiple times done so.  Got so far as having it back in the body with the semi auto functioning (but requiring the 'reset" after a couple of trigger pulls) and then it happened again.  Grabbed one of my older replicas out of the closet that I had suspicion had the same issue (guy I had loaned it to during a game was having issues with the semi that the old reset trick was not fully solving) also turns out to be having the same issue.

https://imgur.com/crl7XCz

That be the current state atm.

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Wait, are you running it on a stick nimh battery?

You might find that the issue is caused by your battery not having the current output required to reliably turn the gearbox over.

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That one there is a stick 9.6v nimh tenergy.  Worked well enough on all my guns with a shs high torque motor, stock gear sets, under 400 fps springs, etc.  What I've been using till the recent attempt to swap certain guns wire sets out for better wiring with deans. 

Just had one of the lipo ones go down today at the field, though I think either a bb got into it or something else is getting the gears stuck.

As for the lct gearbox, one of the event hosts when I was chatting with him mentioned that perhaps the trigger spring is too strong and is pushing up against the trolley and switch assembly.

I have come to the conclusion that I am cursed either way, but I am going to go at it again after work tomorrow and see if swapping the trigger spring will do the trick, and if so take a look at at the other tow ko'd gearboxes.  At least I got a table now to pound hands on in frustration.  If all else fails throw more money somewhere.

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Everything but the spring (which was downgraded) and the motor is the typical stuff found in an lct brand gearbox (lct branded 16:1 gears iirc, the zipper sounding ribbed cylinder, red poly piston with metal teeth, what was an aluminum cylinder head before its nozzle broke off, etc.)

Earlier I almost had it after swapping the trigger spring out for a thinner/less coiled one, except even with a fresh charge the motor would turn the gears, piston teeth probably not catching with gear teeth properly or something.

The other gearbox had a somewhat amusing reason as to why it broke down midgame: the spring guide broke and was lodge in the spring after bashing the piston head off.  Had it all sorted out but whilst trying to get the shell back together the same *fruitcage* little metal tab on the trigger switch portion of the MODIFY wire harness somehow sheared itself off despite having nothing near it...

Pretty much heartbreaking.  Debating whether to ask on local (albeit pretty much dead) forum for a tech to rebuild these gearboxes or just go full nuclear and get either a bunch a cymas from a shop and pay to have them also change the connectors out or go get a full lonex gearbox (except the one shop that has one in stock stateside also doesn't do tech work.)

Edited by Gunmane

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Well, another option would be to get LCT trigger switch units to swap in, if your problems are all with the trigger unit. I suspect that whatever trigger switch unit you're using isn't interfacing properly with your cut off lever, but it's hard to say without it in hand. I'd offer to help fix it but shipping a steel RPK from Michigan to Scotland and back will be eye-wateringly expensive.

https://www.wgcshop.com/products?search_From=searchItem&item=lct-buttstock-switch-assembly-for-ak-series&search=special&rs=lct switch&catid=&cat=&view_choice=a

https://www.wgcshop.com/products?search_From=searchItem&item=lct-handguard-switch-assembly-for-ak-series&search=special&rs=lct switch&catid=&cat=&view_choice=a

Alternatively, Lonex make good trigger switch units.

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I have the original one in it atm.  Found out through some digging that apparently LCTs are known to have issues with the selector plates (with it being off spec to anyone else as well), as this issue has occurred to others as well.  Just going to accept it as an full auto gearbox after I got it functioning again.  Bit annoying I could not find that out before I got into this mess.

The other gearbox was not playing nice with any other trigger switch unit all evening yesterday other than the original one with built in fuse. so got that one back together but not tested it yet.

Plan is to test it and possibly peak inside the third gearbox to find what is wrong with it and then await the soldering iron I ordered and play "do I have enough brain cells to solder deans on and not burn myself or the house horribly?".  My main question in regards to all that is should I just keep the fuses or bypass them entirely?  The LCT gearbox can already do that at the cost of not having the buttstock space (unless I go get something like the GATE extension piece or build one like it), but the acm gearboxes with the fuse lines built in are another story.

 

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A surefire (but expensive) way to solve the issue would be to drop in a V3 Titan or some other computerized mosfet that doesn't use a cut off lever.

Have you tried swapping out the cut-off lever and/or selector plate? SHS make a cheap steel CoL and selector plates should be easy to find (CYMA ones are cheap, cheerful and pretty indestructable).

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