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TDC mod to AEP

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Just a quick show-and-tell.  I've flat hopped my AEP and inserted an eraser rubber nub, as can be seen in plenty of YouTube how-tos.  However, a problem immediately became apparent.


The stock hop lever is operated by a wheel that presses down on one side of it only.  When putting pressure on the rubber, the hop arm was visibly skewing inside the hop unit.  There was also small but visible vertical play on the arm when I pushed a BB through the hop.


So, what to do?


I'm trying a Top Dead Centre modification, rigging a screw to press down directly onto the hop arm from above.  In this case, the screw goes directly through the upper (fixed) slide of the gun, as there's no room for any extra mechanism inside.


Here's the hop arm with the new nub stuck on, and the wheel already removed.





Next, I marked the body on body sides in line with centre of the hop cutout.  Putting the (solid) slide back on, I ran a strip of tape over the top of it between the marks on the body, so that its edge was also aligned with the hop.  I then took a centre punch and whacked it in at top dead centre of that edge line, which should be directly above the hop cutout.


On the CYMA CM.123 it turns out that this point is precisely on the shoulder of the fake slide cutout, which actually made punching and drilling a straight hole somewhat tricky.  Decent drill bits and patience did the trick though and I drilled it out to 3.5mm (3.2mm would actually be better) then tapped to M4.


Inserting a 4mm bolt through the hole, I could feel it pressing down on the hop arm.


This was confirmed by checking visually that it was marking the hop arm.  Here it is after some mucking around - I'll probably stick a thin piece of metal or sacrificial plastic on there.  It could be up to a mm or so further to the rear, but it was a tricky position on this particular gun.  You can do better.





Then it was just a case of cutting a piece off the end of the bolt to act as a grub screw, cutting a slot in it to allow it to be screwed in and out (it needs to be out to put the slide on and off and change the battery), and wrapping some PTFE tape around it to snug it up in the fairly shallow tapped hole.


Here it is in place on the slide, fully screwed out.  Note the awkward location, right on the shoulder of that break in the slide.




On a flatter slide you could put the screw in, wind a thin nut down it and glue that onto the slide to effectively deepen the hole.  If I were doing it again on this gun, I'd fill the end of that fake cutout with chemical metal first then drill and tap through the whole lot.


It presses down directly on the centre of the hop arm, (almost) right above the nub and barrel cutout, so it should - famous last words - allow for consistent pressure.  I'll find out tomorrow.


Does it get in the way of the sight picture?  Sight for yourself.  You can just about make it out when fully screwed out, but it won't be fully screwed out and it's not distracting.





I'm quite pleased with that.  It's a non-destructive mod apart from the easily filled hole, and the original wheel can go right back on if it doesn't work out.


While typing this, it's occurred that I could even run them both together: dial in the hop using the wheel with the slide off, then put the silde on and snug the grub screw down to hold the hop arm firmly in place.  I might try that.


Tools required:

Centre punch.

Drill bits up to some amount shy of 4mm.

M4-0.7 tap

M4-0.7 bolt.


PTFE tape / dental floss.


Time required:

Under an hour for the first one, including measuring twice.  A Dremel style electrotool will speed up the bolt cutting and slotting.


Skill level:

Hamfist. If I can bodge it, you can bodge it.





Gloriously pointless.  With the minimum hop that I could put on with the TDC screw, I was massively over-hopped for 0.25g.  0.2g emerged in spluttery clusters.


Don't do this with an AEP unless you've significantly increased the energy.  It's for the lulz only.


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I find the TDC on my MK23 is pretty rubbish. Was shooting perfect till I put it on :( 

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As I said in another thread , my TDC mod on the MK23 massively overhops anything below .4 with minimal hop applied lol. Kinda pointless to put it on anything if you plan to use lighter bbs, but at least it lets you keep the original hop up wheel :D

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Well my mags all seem fecked so once I have em sorted I am taking the TDC off, setting it back to normal and having a play with it before I take it out again.


Will get it sorted, bloody need too, its like a primary weapon for me lol

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Heh, nice bump.  I should probably have been crystal clearer up front that I did this in the spirit of experimentation, and I can confirm what LightningCh said that the absolute minimum amount that I can put on with it is excessive.  The stock windy-wheel works better.

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