CA 36 v3 mechbox problems - long read

[m102404]

Looking for helpful suggestions and guidance on getting this mechbox working. It'll be a bit long but hopefully all the info is there. (I'm also venting frustration, so it might be a bit wordy)

Background:
Bought a CA 36 from a guy off the forum (undyne - "Totally locked up CA36" post in this section about 2 weeks ago). What undyne related was that he bought it new and it was working fine and then seized up. Very infrequent use, mostly at home. Stock CA internals, never taken apart and not upgraded. He took it apart and had problems putting it back together. Finally had it going and it locked up again. Then sold it to me and wished me luck (and here I am!! haha).

I don't have a working/exisiting v3 mechbox to reference, but have decent experience with the v2.

So far:
I've disassembled and swapped stuff in and out about 20+ times so this is more of a summary than a chronological history of what I've tried so far.
When I got it, the gears looked fine but there major issues with the shimming (some too loose, others jammed tight). Another issue was that the side plate that screws onto the right side of the mechbox that has the cross-frame pin hole and that traps a small spring was really loosely screwed on. As a note, the grease that was in there (very little to start with) was basically solidified. Maybe as a consequence the grease drying out, the piston head was "glued" to the cylinder head. I had to pull hard-ish to get that out. Also, the fuse assembly was removed.

I reshimmed (fairly decently I think), regreased and reassembled (all stock parts). Nothing. Motor would try to crank but wouldn't make it past the initial "clunk". No spring pull at all.

Eventually I found that the screw (outside right side of mechbox) that was loose to begin with was protruding into the mechbox by a good 1mm when tightened up and jamming/squeezing the internal switch assembly. This would cause the sliding portion of the switch to pinch/jam in the forward/on position. This was undoubtedly why there was some melting and scorching on the wires and connections (i.e. just like holding the trigger down while everything is seized up). All of the copper contacts are extremely brittle. I ground down the screw so it was flush with the inside of the mechbox. I then found that the body/left-fin of the sliding part of the switch was rubbing against the cut-off lever, preventing the lever from full travelling fully. I sanded just enough for clearance and that seemed to smooth out the workings of the switch assembly.

Eventually, I ended up swapping in a TM cylinder, cylinder head and v3 bearing spring guide. I found that after assembly, it might fire once or twice and then seize.

At one point I resoldered all of the wiring as the stock wires were already in bad shape and there were nicks in the shielding. I shrink wrapped all the terminals to make sure I wasn't getting a short. I also checked the mini-tamiya plugs to make sure I was getting a good solid connection. I checked the motor brushes and commutator and it looks ok. Obviously, I checked that the motor spins freely with direct power. In fact assembled with everything but the spring guide, spring and piston, the mechbox runs great.

I swapped in a spare set of TM gears and reshimmed. I also swapped in a stock TM spring. And it worked.

So, I got it to the point where it was firing single and maybe full auto, then it quit again. I had replaced the selector plate and readjusted the finger contacts on the left side of the switch assembly. Put about 500 shots through it. And then it quit again.

Last disassembly. Found that a tooth from the transfer gear had broken off, thankfully it stuck to a corner of the mechbox where a spot of grease was. I also found that one of the finger contacts that touches the selector plate had broken. I swapped all the gears back to CA gears, made a new contact from copper sheeting, reshimmed, regreased (fairly lightly) and reassembled. It fired twice on single and fired a burst on full. Then it stopped, locked up.

Throughout these trials, I noticed that the tappet plate "fin" doesn't seem to have enough clearance for the selector gear nubbin to travel around completely, without bending (arcing up) the back end of the tappet plate. I found this odd since the tappet plate should run straight back in rails molded into the mechbox case. I took just a little off the tappet plate fin to give a little clearance.

As an overall note, with each reassembly, before I put the cylinder, spring and spring guide in, I've done a "non-tensioned" resassembly to test the electricals and trigger function (the only thing under tension is the tappet plate. Everything spins freely and on demand (i.e. single, full, single, full, etc..). Then under tension (i.e. spring and everything else in, it binds up after maybe a couple of shots.

Questions:
1. HELP! Don't know what to do next. I'd like to get this running well and reliably for June 24th.
2. I've noticed that, fully assembled, that the nozzel does not return to the fully extended position, but rather to a retracted position. When it fires, the nozzel will move forward and then aft again (almost like an open bolt SMG). Not having another v3 mechbox to compare against, is this normal? I would not think so. Could the tappet plate be jamming and sticking rearward?
3. Could it be a weak motor? It seemed to work with a stock TM spring, but wouldn't pull the stock CA spring and wouldn't ever budge a PPA120 spring. Don't know and don't have a short neck motor to swap in.

Is it a combo of an abused motor and jamming tappet plate, that's causing the mechbox to bind?

I'm stuck, and tired from staying up late every night trying to get this working. Adding up all the spare parts trying to get this going, it'll be close to buying a new complete mechbox...but I'm stuborn and want to see this work properly.

Help please and thank you,

Tys

[The Saint]

Throughout these trials, I noticed that the tappet plate "fin" doesn't seem to have enough clearance for the selector gear nubbin to travel around completely, without bending (arcing up) the back end of the tappet plate. I found this odd since the tappet plate should run straight back in rails molded into the mechbox case. I took just a little off the tappet plate fin to give a little clearance.

Bending (arcing up) which way? Like, towards you (up and away from the gear)? If it's only up and away from the gear, that's normal. All you had to do was to shift the tappet forward until it cleared that rod on the gear or rotated the gear until the rod is not underneath and proping up the rear of the tappet.

2. I've noticed that, fully assembled, that the nozzel does not return to the fully extended position, but rather to a retracted position. When it fires, the nozzel will move forward and then aft again (almost like an open bolt SMG). Not having another v3 mechbox to compare against, is this normal? I would not think so. Could the tappet plate be jamming and sticking rearward?

That's normal, no need to worry about it.

[m102404]

Thanks for the quick hits on the thread guys, appreciate it.

Fully charged 8.4 1400mah minis. I have 4 of them and have been trying them all out during testing. When the gun quit at the FTF game (before we even got started), I used 2 of those batteries in my M4 and they seemed "normal".

Yeah, the tappet plate thing is hard to describe. When non-tensioned assembled, and the mechbox open, when I manually rotate the sector gear, the nubbin will engage the tappet plate fin and start to move it back. Just when it starts its downward travel (around 11 o'clock-ish) it seems to run out of room (i.e. the tappet plate is all the way back, nozzel flush with cylinder head front face and edge of cylinder). Oriented with the left side of the mechbox laying down on table, nozzle pointed right (just like most pictures). The left/rear end of the tappet plate has to bend up (i.e. into where the cylinder/spring would be) for the nubbin to clear and finish its rotation. It seems to be excessive.

Assembly hasn't been a problem, fiddly and a pain but normal. Things seem to go together with that satisfying "click" where everything "feels" good. Hard to describe. When assembling, I've tried to keep the nubbin indexed at 1 o'clock, but maybe a touch more forward, but so it's just ahead of the tappet plate fin.

I'm wondering if the tappet plate fin is getting jammed between the nubbin tip and the mechbox case (right half). Not during assembly but after it's gone through some firing cycles. I've only got 1 thick shim on top of the sector gear (think it's 0.5mm) and there's almost no side to side play with that gear when the mechbox is closed and screwed tight. I'll check for wear marks on the inside face of the fin when I have it open again (which will probably be tonight).

[deep in the bush]

Ok I had my G36 looked at by a whole army (no pun intended..ok a lil) of people...I had everything from too small of wire to bad shims...it turned out it was the cylinder in the mechbox it self...make sure its flush with back of mexhbox moulding. the piston head can get stuck in the space if it is not flush. That turned out to be the issue with "ole betsy" after i replaced everythng but the cylinder and mechbox...ha ha ha...one of life's 200 dollar lessons..at least i now have kicking new mech box!!!

deep

[m102404]

FIXED - for now.

Bought a new motor from airsoftparts.ca (thumbs up!!!). Swapped out the original stock CA motor with a new TM eg1000s. Broke down the mechbox again, checked everything (no obvious problems with the tappet plate), regreased a little, reshimmed and swapped out to a PPA120 spring (supposed to be like the systema M120) with 3 coils cut off.

At this point I was going for broke. It would either work or I would shelve the whole thing until I got a new confirmed working mechbox for a drop-in.

Re-assembled and ta-da, it works like a charm. Single, no prob. Full, no prob. Switch back and forth between the two, no prob.

Went through a hicap and a half testing, chronographing and sighting in. Not a hitch throughout. Shoots 372 fps, +/- 3 fps, with 0.25. Shouldn't have cut those 3 coils off but I'm not touching it now except to adjust the hop up in the field and to swap batteries.

So...in the end. The motor was the biggest culprit. Excessively long screws and improper fit of parts compounded the issues.

Lessons learned:
- have confirmed working spare parts on hand to swap in and out
- be patient, and then more patient
- I hate shimming the same mechbox over and over and over and over....

This mechbox ended up with:
- stock gears
- assortment of shims
- PPA120 spring (-3 coils)
- TM piston+head
- TM cylinder (unported and scavenged from a v2 mechbox)
- TM cylinder head
- half-home made switch assembly
- new wiring
- TM eg1000s motor
- slightly modified stock tappet plate
- stock nozzle

Won't win any beauty prizes but it works. At least for now. Fingers crossed for the first field test!!!