M4A1 Gen8 Gearbox issues

Wondering if someone might be able to help me out.

Bought a new JM M4A1 gen8 put some metal gears in It, shimmed them and added a 1.2mm unequal spring… managed to empty one magazine through it before it suddenly jammed.

The motor works fine and everything seems to be good but I’ve pulled apart the blaster more than four times now because I’ll get it working briefly again and then it will jam once more.

Everything seems seated in place yet for some reason it’s still jamming… its currently sitting on my desk in it’s 5th tear down is it cursed or am I being a bonehead somewhere and messing something up

Hey brother welcome to gbf when you say it’s jamming have you worked out where it’s jamming is it the piston, gears or motor? But don’t stress about how many times you send it back to the drawing board that’s part of modding and tweeking your blaster trying to iron out the creases till it’s running the way you want. I couldn’t even count the amount of times I’ve had to pull all mine apart. Especially my JM scar V2 I was determined to get it’s fps and rof to limits and now it’s fps averaging 310-330 and rof is have had it at well over 60 but that took slot of playing at to get that to where it is

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Thanks for the welcome!
Should see me around a fair bit now.

When it jams it feels like it could be one of the springs? Like the motor wants to work but the plunger spring doesn’t want to either compress or release.

As far as I can tell the gears or the motor shouldn’t be the problem I swear I have them shimmed and seated properly and motor runs fine on it’s own.

Has me stumped… currently got it working so will put everything back together and see how it goes! readjusted shim height, oiled the bearings and replaced the tappet spring with a different one.

That SCAR sounds like a nice machine! Hopefully I can slowly push this m4a1 to its maximum once I figure out this jamming issue and the other nuances that come with modding gel blasters haha

is it a stock motor ?

if it is it has not enough grunt to push that spring put stock spring in and if it works that was your problem

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Nice work Dave was about to ask that lol. And if you then realise you want to upgrade the motor my advice would be to put enough money aside as if your wanting mad fps and rof then get the red/ chi Hai their 37000rpm, and to power that will need the battery to be 11v and might as well swap the gears to metal as the stock one will strip in notime from the better motor and battery. And also the trigger switch from 5mah to 10mah

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Seems to be running now! emptied two magazines through it no problems except for a bit of slowing down in ROF if I hold trigger for too long…fuckyevboizzz!! Will drain a battery through it and hopefully it holds up.

I think it was the 1.2 unequal spring i had in there, as dave suggested i switched back to whatever spring it was that comes with those nylon singularity gear cases.

Presumed stock motor would be able to handle the compression but I guess not? Either that, my initial shimming was messed up or the tappet spring I replaced was wrecked.

Will replace motor anyway though.
Chihai red = more torque right?

Also gear ratios 18:1 or 13:1? my understanding is lower is faster?

I think u mean 5amp to 10amp for the switch not mah.

Yer I did typo due to big hands typing on a small touch screen keyboard on the phone. Yer the motor I got is high torque and high speed. Picked it up on eBay $45 or if you don’t want to wait for shipping from China their around $80 locally

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Lower ratio are speed gear sets and high is ratio is high torque I’ve got 12:1 black shs gears in one of mine and it’s still pumping over 300rps plus rof is crazy and they were well worth it and weren’t as pricey as some of the others.

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Shot well for another two magazines then started going weird…shooting multiple gels, erratic velocity or they would just fall out of barrel.

Presuming a pressure leak in the cylinder head or somewhere around the nozzle is the culprit?

Was the barrel, sat loose in the t-piece and t-piece wasn’t sitting tight either… bunch of mashed up gels around the nozzle and t piece.

10a Omron switch should be fine? Don’t really want to mess with mosfets just yet and read that these bigger motors need mosfets, haven’t much idea about switches.

Also looking at the chihai m150, should be able to jam that in a Gen 8 M4 if I customize the handle but again probably going to need mosfet?

Uhh h yeaaa so function over form riiight?
Viva la Bush pig…

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What happened to it ?

Either the shimming was bad or the 1.2mm unequal spring was the Problem, stock motor couldn’t handle the metal gears and higher tension so would jam or my shimming was misaligned creating the jam.

Then I had misfire problems due to a weak tappet spring or compression leaks around the t-piece, replaced tappet spring and used plumbing tape around the t-piece and barrel seemed to have fixed the problem.

Runs really well now! Took it to a skirmish yesterday and it performed without a problem.

Just need to get a new motor to run a higher tension spring and cut down that 40cm barrel then I’ll be satisfied.

I had one of my Gen9’s do something like that and it turned out to be the ‘anti-backwards’ doohicky in the gearbox … the spring wasn’t engaged (spring not fitted correctly… my bad):smirk: