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Tokyo Marui SOPMOD M4 Disassembly Guide
Tokyo Marui SOPMOD M4 Disassembly Guide

This is taken from the guide made by FIRST Gun Shop in Osaka, translated to English by me. Big Grin

There's a bit of discussion over in that thread but it's mostly in Filipino.

I hope this helps those who wants to mod their SOPMODs.
Thx mate! Much appreciated!
I'm interested to see how the recoil engine works, is there a disasembly of those parts somewhere?
Here's the recoil :-
[Image: MechBoxRecoil.jpg]

With Mechbox Open :-
* To take notice of 1/2 tooth piston, but also proprietary (knotch on the top bit, not visible in this picture)
* Standard Piston Head
* Standard cylinder usable
[Image: MechboxOpenCompare.jpg]

Spring length compare :-
* same length as standard
* "feel" wise, it feels somewhat stiffer than an M120 SystemA. But no real "proof" in terms of Joule tests
[Image: SpringCompare.jpg]

Battery case :-
* room for one more cell Big Grin
[Image: Battery.jpg]

I've not worked out how to dismantle the outer barrel yet (or more specifically real barrel collar nut of the delta ring).
What are the other springs shown together with the piston?

Also, will changing the piston head do nothing to the blowback engine? I am under the impression that the piston will push the rod that goes through the spring guide to work the blowback.

Might open up mine over the weekend to see for myself.
The other two springs above are standard springs to show that the Sopmod uses standard length springs.

I think the piston head can be changed safely. It wont' impact the blowback engine. The piston itself is proprietary (it's got a knotch on the top to make the port cover open up). So what you say is true though, that when the piston winds back, it compresses the spring against piston guide which in turn the recoil block, then recoil block to the short spring @ the back.

If you open yours up can you please find out if your cylinder is ported? Mine isn't! And I"m a little bit surrpised 'cos the 1st JP one in the link you gave is ported.
Mine doesn't seem to be ported (I changed the inner barrel so I saw the cylinder). Apparently the makers of the JP guide already changed their cylinder. I will change the cylinder on mine too (Prometheus Type B) and see if I can change the piston head and spring with no problems - once I get the parts.
i already changed the spring on mine and the cylinder is not ported.

also the spring is shorter because the innerside of the pistonhead is thicker on the outside radius and there is another thingy on the center of it... this is the one that pushes the brass-colored recoil shaft.

so if you change the pistonhead to standard ones available in the matrket, the middle screw of the pistonhead will be the one pushing back the recoil shaft, which might damaged the head of the screw in my opinion.
So I picked up a Prometheus Piston head. You cannot use the ball bearings/spacers but just the piston head, the screw, and the black plastic screw collar. It's the screw and the screw collar that pushes that brass rod of the blowback engine. Will see how durable it goes.

As to the spring strength, you can use normal ratings.
I wonder... Will the Prometheus piston head for version 9 (AK74 blowback) work? The springs for version 9 (also by Prometheus) also seem shorter from what I remember. I'll try to check them out when I go to Tamtam.
I did this spring test last night (on Arnies :-

I'm having problems trying to reach the sweet spot of this weapon, and silly me, I never Joule tested it @ stock. Using a PDI 375mm 6.01mm inner barrel, and soft FireFly buckings, the following are the results I get with various brands and power of springs :-

Hurricane M100 - 113-116ms (370-380fps)
Phoenix MP100SP - 113-116ms
Phoenix MP90SP - 108ms (354fps)
Angel 0.9J - 108ms
SystemA M85 - 93-95ms (305-311fps)

I'm trying to get as close as possible to 0.989J (approx 325fps) but just can't get it . There's such a big jump between the SystemA M85 -> Phoenix MP90SP. I guess I'm comparing different brands here, so maybe comparing apples/oranges.

Note: Be careful with spring guide spacers, lockups seem to occur more frequently on this mechbox/EBB design.
Phoenix MP90 is a really strong spring. Not really comparable to a Systema M85. I wonder how you put the springs into the piston if you guys are using "normal" piston heads? Isn't the inner part of the piston not round, making it impossible to fit full-length springs?
Can someone provide me with clear images of the upper reciever locking nut (delta ring) thread. this part of the gun:

[Image: DRM-COVER_01.jpg]

And also of the Delta ring. As I want to know how it all fits together before making a purchase
Will this do?
[Image: DSC00045.jpg]
The sprocket-looking thingy at the left is attached to the barrel by a Philips screw located at the underside. Remove that, you remove the ring that holds the RIS (rightmost, largest), and the spring. After removing that, you gain access to the nut (second from left, black, below spring). The thread is right-hand (clockwise). I used the lock ring wrench shown to remove the nut. The silver thing there is what holds the outer barrel. According to some shops, replacing the delta ring with a G&P one will enable you to attach other types of RIS.
I need to get that silver tool!! I've already damaged a little bit of the barrel nut trying to unscrew it. You're the man!!

Tonight I was gonna Dremel my MUR to fit in the Sopmod (to replace the upper receiver).

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