First time modder- need some help

Hey guys,

So I bought a j10 acr to learn how to mod.
I had my first attempt at pulling it apart last night and its fun (and a bit scary).

I upgraded to a green o ring and 1.3mm spring.

I think I put it all back together correctly, but i really have no clue.
I mucked around with it for a few hours, studying where everything was and trying to visualise how it all works. I put it back together as best i could…
I wasnt sure about the gear position for the top gear that connects with the plunger, but it seems to have aligned itself.

The result? It fires! The upgrades Seem to have improved the power of the shots compared to stock, as was the plan. I have put about 5 or 6 mags through it and so far, so good…

I did notice however, that when I release the trigger it almost does like a half pump/cycle and gently lobs out a gel.
It also seems to shoot 2 gels at once every 2-4 shots. Like they shoot out side by side and follow the same path.

I am just curious if any of this is normal after upgrading the o ring and spring or if i have missed something when putting it back together/done something wrong.

Any help/ideas/experiences/etc you can provide would be greatly appreciated.

Thanks everyone

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Hey hey and welcome victim number upteenth…

As a starter you’ve done pretty well to have no issues with your first gen9 rebuild. They can be tricky for noobs

Sector gear alignment: yea, it will self align with the piston ladder but usually I rotate it so the piston moves freely and the tappet tail isn’t contacting the nub that pulls the tappet back

Run on: is also normal. An active brake MOSFET solves this but most people don’t bother.

There is a center screw in the base of the motor plate. Do not play with this until you start to learn shimming…which it sounds like you will soon.

Next up for you though …barrel and hopup. A decent spring retainer is gold and having a bearing inside your piston makes for a better outcome too.

I’ve also moved away from mm rated springs opting instead for m or sp rated. Essentially they are better quality and give more consistent results across springs.


Hi Hamish,
Thanks for your reply.
Yeah i was pretty proud that it fired. I was about to order a new gearbox as I didn’t have any Faith.
I watched all the YouTube’s I could on the subject, but sometimes they skip over some things or didnt experience the same issues as i did.

40cm alloy Barrel, hop up and outter barrel stabliser are in the mail. The spring and O ring arrived first so I started with them…barrel seems so easy compared to the O ring so they should be nice easy mods…

I take it “run on” is that last little half shot that it does?

There is no motor height adjustment on the acr, so I’ve learned…apparently it aligns itself perfectly with stock pistol grip cap thing.

Is the two shots at once thing normal too?


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The extra after trigger, run on

It’s basically momentum in the system


It could also be the anti reverse latch


So if its firing mag after mag without major issue, everything is as good as can be expected for a toy that i have made work beyond its normal limits?


I wouldn’t expect gels to feed

AR latch is a good gotcha though

You have yet to find it’s limits m8…

Push it…push it real good…


If the piston stops half way or more back and the anti reverse is not working correctly it can go back forward again pushing a ball out


Yeah the anti reverse popped off and i wasnt sure how it went back in…
I did my best with it and when testing it out before sealing up the gearbox, it didn’t let the gear spin the other way and made a nice clicking noise when I spun the gears to correct way


It’s worth mentioning that the polarity of the motor is quite specific also

An uncommon thing for people to do it at least, uncommon they report it

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Just a quick tip that I’ve found useful, use your phone to take photos from all angles as you pull apart a new blaster, they make handy references of position and order of assembly when things need to go back together.


Hey zeHamish,

I’ve never understood the benefits of a decent spring retainer on decent nylon gearboxes. Do you still need one if there is a bearing as part of the plunger\nozzle mount? What are the benefits?

A decent spring retainer is gold and having a bearing inside your piston makes for a better outcome too.

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Having one is great, having two is better

A spring retainer that bolts through stops the spring from bending during compression.

Having bearings on both ends makes the decompression smoother

Two bearings is a minor benefit but worth it if you are chasing a smooth machine with consistent results


Yup, with a bearing at each end of the spring allows the spring to always work at it’s best potential… With no bearings, the spring can wind itself up and make it have more, or less (irregular) potential energy… A spring at each end lets the the spring relax between compressions…:+1:

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Hi sir, i am also new to modding,
recently purchased my first blaster from a mate as he not longer play :smiley:
I am just wondering when you said “bearing inside the piston”, do you mean upgrading the o-rings?
or there is an extra piece u can put inside the piston?

You can buy both a spring retainer and a piston head that have inbuilt thrust bearing on them, it stops the spring from winding up


can u show me a link or pic of the “inbuilt thrust bearing” O_O?



Arh them, I was wondering what those ball bearinged washer thing does, now I know

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