Decided to have a crack, pulling the UMP 45 apart.
While working , its fps had dropped quite a bit ( from 290-160) and it was a bit noisy.
Followed the low guido teardown vid.
The blaster comes apart quite easily. More should be designed like this.
The external mosfet had me a little concerned, but treading gently around it should work.
Guido doesn’t use rubber gloves / touches it with his bare hands, so maybe i was a bit overly worried about frying it with static electricity.
Got it pulled apart, and the problem was obvious…
It looks like a two stage piston head, has come apart inside the cylinder…
So, it was rattling around loose inside the cylinder.
This is a v3 gearbox.
Do they all come with double thickness piston heads.?
Like double o-rings, just a lame experiment.?
Should i chase another stock one, or fit a standard piston head.?
Will a v2 Piston head fit.?
Anyone else had this issue…??
Waiting for WAT / Xforce to open…
What’s the loose bit made of? Same material as the piston head? Almost looks 3D printed.
Usually piston heads have rubber pads on the end of them, maybe this one corrects AOE. 
Looks like just a glue back in jobbie to me… it’ll key rotation wise on those moulded star lines.
yeah, its the same material as the piston head.
An additional outer layer.
It does clip into the detent…but comes out very easily.
I suspect a layer of glue might not have it clip in intimately…and not last long.
High reciprocating loads.
Probably better off, with a solid one piece head.
I thought about greasing the dry gears…but seem to remember being told…Dont.
With the external mosfet, grease could get flung out, build up, and ruin it.
Interestingly, the AR latch doesn’t seem to engage…return spring is weak and flimsy…
Yes piston and piston heads are the same.
Yeah, no glue’s ever going to be permanent… unless you put a shock pad in the cylinder, but it should already have one on the back of the cylinder head.
Might want to check AOE if you fit a new thinner one, it’ll change. maybe for the better, knowing China. 
Yeah definitely recommend another piston head and checking the AOE after fitting.
The grease thing is for Optical Pickup type FCU’s, which I’m not sure what type is fitted to these, optical or magnetic pickup?
Grease can cause a film to build up on the lense of the Optical Sensor and cause issues, requiring constant stripdowns to keep the lense clean.
If its a magnetic pickup type, then grease isn’t such an issue. 
What is angle of engagement, and how do you check it…?
I think it’s magnetic…WAT tech back 2morrow…
AOE is “angle of engagement” between the first tooth (pickup tooth) on the sector gear and the first tooth on the piston rack.
Correct AOE should see the sector pickup tooth engaging with full contact on the rack tooth. If the piston is too far forward the pickup tooth will contact at the tip of the tooth before full engagement.
Generally people correct AOE with rubber discs or similar to put the piston in the right spot under full spring tension to guarantee proper engagement.
Incorrect AOE will cause premature wear of your sector gear.
Here ya go. A picture’s worth a thousand words, a video is worth a million. 
So, getting a (o)Ring, means an engagement.?.?
Got it…
It follows, that divorce is subsequent separation, and catastrophic…
For what it’s worth, any V2 piston head will do the job nicely.
As long as it’s got big arseholes so it doesn’t suction, it’s good to go. The o ring sealing on the inner of the cylinder is where it’s at.
That o ring doesn’t care if the air acting on it is coming through an expensive alloy head or a nylon one, in reality. They all work.
Productive gel day…
All back together, and functioning.
I got a new piston head from xforce, a new v3 spring kit with a stiffer AR spring. I have the xforce bearing lube/grease kit so i did the following…
AR latch was quite stiff in the post, so a lot of dry movement to wear it in a bit, then lube on the post with the new stiffer spring. Moving much better now.
Painted on a VERY thin layer of gear grease with an art paintbrush, a very light coating.
The V3 gearboxes are a dream to put back together, the gears sit properly in position with very little movement. Sector and crown gear went straight into their upper slots. Only the bevel gear needed a bit of lateral movement to go back in.
Clunk…and its back together … that easy…
Whats that i left out .? Oh, only the piston…!!! Open it up, and do it all again.
Clunk… Back together again… Easy.
All the wires on the outside makes it a lot easier too…
Fitted motor cage, make test firing easy, before re-assembly.
Mosfet still runs fine, circuit board anxiety for nothing…
Anyway, performance is much better now.
That was a high figure, now averaging around 280-300 with xforce pinkies.
They are a bit old, ill brew up a fresh batch, and try some ihobby whites.
Its still a noisy clunker…!!
Even with blowback removed.
Funny thing, re mags.
I ordered some from M416, as they were all sold out in OZ.
They arrived, but the terminals are spaced slightly differently…
Original mag on the left.
The one on the right doesnt get power and feed…mag springs must not be making contact.
What would be the best way to add some conducting girth to the contacts to widen them…just add some solder…?
“Its wouldn’t be gel, if you didn’t have to screw with it…!!”
Anyway, im happy its back up and running.
Got an itching to try a dinosaur gen8 now…
Grandpa wants a run, out of the rocking chair…!!
I can start by putting some white / red food coloring paste, on the fire select switch decals…
If the new mag’s terminals are closer together there should still be contact… looks like there’s plenty of metal there. Maybe the terminal plates on the newie are set deeper and your springs can’t reach?
Good idea too to check the new mag out with a 9v battery to rule out a faulty motor or bad wiring.
Yeah, I’ve checked the mags with a 9v battery .
All fine.
I tried gently stretching the springs.
Cleaned the terminals with a bit of vinegar.
Still no power.
You can tell, with the auto mag prime, upon insertion.
Nice write up as always and good results!
A rare classic, well worth keeping in good working order!
Cheers…
I was nervous about ruining the mosfet.
It was actually a non issue…just avoid touching as much as possible.
Currently no more spare mosfets, last time I looked.
It’s branded 2020…wow 5 years old already…
Selectable 1-5 round burst is cool, as is selectable mag prime (and duration)
Someone should bring in those mosfet M4s…they’ll sell a truckload…
It’s actually a shame ldt went with such a proprietary gearbox and mosfet setup on these, Airsoft is basically a standard V3 box… but such low volume build definitely keeps working examples value high. True collectors items!
The early UMPs are still one of the best value bang for buck blasters out there.
Nothing wrong with a monster Gen 8 build.
