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Tokyo Marui hop-up mod


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#1 Doctor Kajita

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Posted 30 September 2008 - 07:10 PM

There's been a lot of discussion recently (a lot of it by me) about changing out the stock hop-up unit with a TM one.  Here is my little story about it.  To preface, I must say I am a noob when it comes to Airsoft so I asked a lot of questions.  Therefore, this is for noobs alike.  This is probably very trivial for Airsofts vets, but I thought I would document the process and resources that allowed me to complete this project.  

Thanks go out to xsboredom on Airsoft forum for presenting the idea - http://www.airsoftfo...op-t124264.html - and answering all my PM's about it, Allizard for creating this thread - http://www.airsoftfo...gs-t104274.html, MechBox.com for the videos about how to disassemble/reassemble your gun and gear box, and Joel at AEX Oakland for helping me, free of charge, with a little issue that I will detail below.  Thank goodness for the internet!

I decided to go ahead and just do it for the purpose of being able to fit various buckings on my Prometheus barrel (407mm); specifically, the Firefly bucking.  Many people have had issues fitting the stock hop-up over most aftermarket buckings.  Some people have had no issue.  Unfortunately, I am one of the people that have had issues.

The hard part of this is changing out the air nozzle as you have to take apart the mech box to do so (it's important to have all the right tools and work space to do this...I won't go into detail as this is all on MechBox.com and I'm sure you can find a plethora of info on the web).  However, this gives you a chance to clean it out, re-grease, and add a better o-ring on the piston; I used a x-ring from McMasters.  It's basically an o-ring with squared off edges.  Here's a discussion on that on Airsoft Retreat (you'll see that I participated in that discussion): http://www.airsoftre...p?topic=69098.0.  Anyway, the mech box wasn't as bad as I thought as everything functioned normally (at this point, I did not shoot any BB's yet, just dry fired the gun to make sure everything sounds and feels right).  

Anyway, yesterday I completed my disassembly and reassembly of the entire gun and fitted my CA TM M4/M16 hopup.  I left the stock KWA BB feeder (part# 3) as the CA one didn't seem to fit as good.  The hop-up unit actually had the axle for the middle gear snapped off, but I was able to super glue it back on and the gears seem to turn as good as it could.  The TM hop-up fits a little tighter than the KWA one, but it does fit and it is not an issue, according to Joel at AEX Oakland, who says he has done this mod on many KWA M4's.  I should note that before any of this, I fitted the TM hop-up over my barrel using a Prometheus bucking (soft).  It fit just fine with just a bit of lube.  

So I put everything together and fired a few test shots...nothing.  Darn it!  I spent the entire day making sure I did everything to a T, but the gun wasn't shooting any BB's.  At this point, I decided to take the gun to AEX and ask Joel to help.

He tinkered around a bit and concluded that the problem was my flash hider.  Because the 407mm barrel sticks out the outer barrel a bit (without the flash hider), the flash hider, when tightened all the way, will push the barrel back, causing to mis-align the hop-up unit and nozzle enough to where the BB's will not feed.  The solution, for now, is to not tighten the flash hider all the way.  Not too loose, but not too tight.  Not sure how that will behave during a game - I'll report back.  I think because the TM hop up is a tad bit bigger than the KWA one (read the part where I said it was a tight fit), it has this issue with the longer barrel.  Those with a barrel that does not stick out, should not have this problem.

Hope this helps anyone who decides to do this "mod," if you can call it that.

Edited by Doctor Kajita, 30 September 2008 - 07:13 PM.


#2 Guest_allizard_*

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Posted 30 September 2008 - 10:14 PM

Thanks for the report.  Please keep us up to date with your findings.  

I'm also going to fit a TM hopup unit in our gun.  I just prep one today but haven't install anything yet.

#3 Doctor Kajita

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Posted 30 September 2008 - 10:32 PM

View Postallizard, on Sep 30 2008, 11:14 PM, said:

Thanks for the report.  Please keep us up to date with your findings.  

I'm also going to fit a TM hopup unit in our gun.  I just prep one today but haven't install anything yet.

No problem.  I have a game at CQB City on Saturday and plan to use the gun all day.

The hop-up adjustment wheel is a little difficult to turn since it sits a little behind the opening (bolt catch).  You'll need to keep the charging handle pulled back in order for the wheel to stay exposed.

#4 triple b

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Posted 01 October 2008 - 12:17 PM

I want to just replace the hop up bucking to a hard one because my kwa m4 is shooting 500fps will that solve my issues with the hop system

#5 threadkill

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Posted 01 October 2008 - 04:38 PM

View PostDoctor Kajita, on Sep 30 2008, 11:10 PM, said:

There's been a lot of discussion recently (a lot of it by me) about changing out the stock hop-up unit with a TM one.  Here is my little story about it.  To preface, I must say I am a noob when it comes to Airsoft so I asked a lot of questions.  Therefore, this is for noobs alike.  This is probably very trivial for Airsofts vets, but I thought I would document the process and resources that allowed me to complete this project. ........

Hey Doc,

Thanks a ton for posting your findings and all the great info. Hat's off for the effort and paving the way for the rest of us.

#6 Doctor Kajita

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Posted 04 October 2008 - 10:26 PM

I had some issues with my gun some related and un-related to this mod.  The related part is that the hop-up unit I got was damaged to begin with - the middle gear's axle snapped off and my attempt to super glue it back on was not really a good solution since it wasn't aligned properly.  This resulted in poor fit into the gun and eventual re-break of the axle.  I played the game with no gears except the one that moves the hop-up lever up and down.  Every time I shot, it pushed the lever up, decreasing the hop-up effect.  The good news is that with my Prometheus barrel, a Firefly bucking fits perfectly.

The un-related portion of my issues was something attributed to my take down and re-assembly of the gear box.  The sector gear sounded like it was spinning freely against the piston.  At the game, I took the gear box apart and found nothing was damaged so I reassembled it the best I could.  However, in my haste, I didn't install the trigger back in correctly where it engages the trigger switch, so I never got to fire my gun again.

So, that being said, I do have a new hop-up unit in the mail and I am getting pretty good at taking apart my gear box :)

I just need a backyard to fully test all my work.  More to follow.

#7 vic_man4

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Posted 05 October 2008 - 04:49 PM

View PostDoctor Kajita, on Oct 4 2008, 10:26 PM, said:

I had some issues with my gun some related and un-related to this mod.  The related part is that the hop-up unit I got was damaged to begin with - the middle gear's axle snapped off and my attempt to super glue it back on was not really a good solution since it wasn't aligned properly.  This resulted in poor fit into the gun and eventual re-break of the axle.  I played the game with no gears except the one that moves the hop-up lever up and down.  Every time I shot, it pushed the lever up, decreasing the hop-up effect.  The good news is that with my Prometheus barrel, a Firefly bucking fits perfectly.

The un-related portion of my issues was something attributed to my take down and re-assembly of the gear box.  The sector gear sounded like it was spinning freely against the piston.  At the game, I took the gear box apart and found nothing was damaged so I reassembled it the best I could.  However, in my haste, I didn't install the trigger back in correctly where it engages the trigger switch, so I never got to fire my gun again.

So, that being said, I do have a new hop-up unit in the mail and I am getting pretty good at taking apart my gear box :)

I just need a backyard to fully test all my work.  More to follow.

Sounds good, when I get my Fire Fly bucking, if it doesnt fit then Im going to get a TM Hop Up unit.

#8 SpaceMonky

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Posted 13 October 2008 - 05:25 PM

i'm curious what air nozzle you used? i'm going to be getting the same hop up unit and want to make sure the air nozzle will be compatible.




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