anyone have any experience upgrading their JG Works Sig 551?
any recommendations on the max spring size compatible without destroying the internals?
any other simple performance upgrades available that I could look at doing?
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I have had some experience with them. A few warranty jobs and a handful of upgrades, and a couple of unfortunate gearbox replacements.
I wouldn’t go anything over an m100 without touching more inside. They are cast gears so always bit of a lottery, some will handle an m130! Some will strip stock… most handle m100-m110 but it’s a cast gear lottery you just can’t know until you try.
but the gears aren’t why… The gearbox can be the problem. They are not radiused, and can break.
Now here is the fun, they are quite a dick to pull apart and put back together. So unless you are willing to go through with it I would keep to an m100 maximum.
They can be pretty nasty performers, with not alot of parts if you are willing to change a couple of parts and put in the work.
Piston head, o-ring, nozzle, and motor are good to go… provided you got a motor with a blue end bell as they have neo magnets. Most had these. Some had a weak ferrous magnet with a black end bell. Not many though… if any 
The cylinder head is good, I always put a 2mm “aoe pad” on them, more to help prevent gearbox failure but the aoe correction is a nice byproduct. Also a quick gearbox radius job on all corners of the cylinder opening is highly advised.
Piston is okay, but a nice SHS piston is worth doing if you are in there. Then a set of 16:1 gears will get a slight boost in rps and semi response, if you are like me, send it on 13:1 gears and should have about 25rps on the stock neo motor with a very tasty semi auto, paired with an m100 and the long barrel it is good for 350+fps! (Depending on brand of m100 some are 370fps!). M110 will see about 380fps on most brands.
In short, aoe pad, radius, m100, 13:1 gears, and a piston is all they need to rock hard.
…But not as annoying as the mag terminal block. Video and photo the hell out of that when you pull it apart, and to add to this the whole build is easier if you un solder the trigger block and remove the trigger switch and wires.
In fact, photo everything. The ambi selector and wiring can also give you grief when putting it back together.
The can go really hard, and a long titan 11v stick is a good fit for them and lasts ages. Even seen a few people just dangle the charging wires out the handguard so they never have to pull the battery out. Though I don’t advise leaving batteries in blasters.
Cool blaster, and plenty of potential with few parts and a little work. Be gentle though as external spares almost don’t exist and need to be imported.
Gearboxes are still available, so that’s a plus.
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awesome write up. just the information I’m looking for. thank you
I’ll start small with the m100 and see where the road leads from there, will definitely be taking a lot of pics n videos so I can put it back together again if I decide to go further, definitely want to be able to keep using it lol
I definitely like it, it’s a pretty nice rig
They are a decent blaster, pretty reliable and decent performance stock. Like all JG blasters, the internals are pretty good, don’t need alot to really pump gels out, and the externals are good but not great.
I shoehorned a JG sig box into my old abs plastic wells G36. Also has all the mods listed in my guide but is short 4 teeth. Nice sturdy gearbox with good semi and rate of fire and an old blaster revived!
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Might be a Well ABS blaster but from memory those G36s had a pretty thick shell on them. 
I had one years ago, painted it up, gave it away to a mate… I should have kept it. 
No G36 on my wall now, and I’m not up for dropping a monkey on an LDT from WAT or X-Force. 
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For an abs blaster they are pretty thick and sturdy. I originally got it just to have a G36C because same reason… LDT one was expensive, and with the proprietary mosfet and such I was not keen.
I did see a Jin Ming G36, J15 I believe but never seen them sold. I think opforcedelta had them but didn’t have mags so again thwarted my desire of ownership. Also I think it was the longer G36 not a “C”
That was a fair step back in time, and would definitely be very rare and collectable model Gelbasters today… right down my alley 
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I had the very first G36 with the clear shell. Which is why it got painted up.
There’s a Well M401 with clear receiver for sale up on the Sunny Coast for $40… if only it was a G36, I’d be all over it like stink on fish. 
Plenty of those clear G36’rs down this way they sold like mad. Probly in landfill now Nothing better to do with wingfield…turn it into a dump