Disassemble Gearbox....

[kylescave]

Right, i have a Full metal m4 that was given to me years ago. i have no idea of the brande. the motor and gearbox say nothing. But the gearbox cogs say G&G. its seems to have been modified.

So the trigger does not work now but it was working. i want to replace it, i also want to upgrade other parts. 

My piston has 12 teeth and all the the ones i can find seem to have 14 or 15. Any options? any help wonder be good.

[Iceni]

Take some pictures! There's a tool when you post that allows you to attach them.

Pistons in general aren't normally modified but that doesn't mean it doesn't happen. It is common to have a tooth missing or even a tooth and a half missing at the pickup end of the piston, but removing teeth from the piston head end is sometimes done to make a lazy short stroke.

Without seeing the rest of the gearbox we can't advise you. Take pictures of the piston rack, gears and the motor if possible. That'll at least let us know what sort of modifications  have been done to the gear train.

If you are wanting to spend some money on getting new parts then we can advise on that as well. Typically if you were to want to upgrade the normal upgrades would be:

High torque motor (long type for M4's)
Mosfet (you can get them pre wired for M4's, Either front wired [hand guard], or rear wired [stock]).
Gears if needed, and a piston to suit.
Bearings/bushings
And O-rings for the piston head and cylinder head.

A good place to start looking at parts is AK2M4.

https://www.ak2m4.co.uk/

Don't be tempted to buy anything yet tho as it may be cheaper just to buy a complete new gearbox with wires ect already done that can just be dropped into the gun. I've also sent you a PM.

 

Edited July 27, 2021 by Iceni

[kylescave]

This is what I have it down to so far. Gonna sleep on it for now though. 
 

Come back at it after work tomorrow.

[Iceni]

That's G&P not G&G.

Piston and sector are factory matched, so nothing there has been modified. I'd run with them.

Piston teeth are counted in a funny way, The pickup tooth is ignored, then the 1st tooth and sometimes half of the second can be missing. So your piston is a 13 tooth. The matching sector gear should have 1 tooth more than the piston in your case 14 teeth.

 

We commonly shorten this part of the gear train on purpose for higher speed builds (yours is factor modified so it needs no work), removing 1 or 2 teeth from the pickup side of the sector gear (so it doesn't mess with the tappet timing), It's fairly typical in 13:1 gearset builds matched with a high torque motor. It's not uncommon for a well built gearbox with those modification to be able to do 25 rounds per second with a 7.4v lipo (you would need a chrono to count that). I wouldn't upgrade the gearset and motor just yet tho, get it running first, then once you have more of an idea of what you want it to do and where it is you can start to change things about.

The piston looks to have very little wear.

The gear train in general looks to be spot on.

The wires have a few areas of damage, that could do with some work. If you can use a soldering iron then crack on and rewire - the silver wire from AK2M4 is decent. Don't forget to add connectors for the motor. If you can't solder he does a complete drop in loom with the contacts for just over £10, but it comes with a mini tamiya connector not a deans connector. You can get adapters if you can't solder or don't know someone who can and already have a deans wired battery. If you don't have a battery then get the battery to match the loom. Component shop sell airsoft batteries (airsoft tamiya connectors are wired reverse to RC cars, Deans are the correct polarity) and you can select the connector type you need. But looking at the desk burns someone in your household probably knows how to solder.

 

https://www.ak2m4.co.uk/internal-parts/electrical-parts/gearbox-transparent-wire-16awg-2-metres

https://www.ak2m4.co.uk/internal-parts/trigger-switches/ec-trigger-switch-v2-rear-wired

Some grease and a re-shim - New shims on AK2M4.

 

https://www.ak2m4.co.uk/internal-parts/bushings-shims/zci-shim-set

And an M100 spring for 330fps. It's going to come out a little lower on power due to the lower tooth count on the geartrain, but I'd just go with the lower power unit you get to a skirmish and get on a chrono. It's better to be under the chrono limit and be allowed to play, than to be over and have to hire a gun. A chronograph is a good investment if you are the tinkering type.

 

https://www.ak2m4.co.uk/internal-parts/springs/zci-aeg-spring-m100

 

Also a selector plate to replace that broken one.

https://www.ak2m4.co.uk/internal-parts/selector-plates/rocket-selector-plate-v2

 

And a piston head o-ring.

https://www.ak2m4.co.uk/internal-parts/pistons-heads/piston-head-o-ring-viton-19mm

 

 

 

The only other thing that is worth considering would be the hop rubber and nub. There's a lot of debate over what brand and flavor are best.

Personally I like them soft and preferably cheap.

https://www.bullseyecountrysport.co.uk/gg-cold-resistant-hop-rubber-g-10-061-5537-p.asp

 

I also like the Prometheus purple rubbers, A lot on here will advise the maple leaf 50deg with the proper nub, those however can be pricey.

And a bottle of bb's if you are planning on shooting it.

https://www.bullseyecountrysport.co.uk/asg-airsoft-polished-blaster-020g-bbs-3300-1-bottle-ammo-target-6mm-19402-35047-p.asp

Edited July 28, 2021 by Iceni