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King Arms M4A1, Factory Defect or Unlucky?


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Old August 13th, 2012, 00:25   #1
IroningMan's Avatar
Join Date: Apr 2012
Location: Toronto
Arrow King Arms M4A1, Factory Defect or Unlucky?

After getting suggestions from my friend, and reading multiple reviews on Airsoft Canada, I got my King Arms M4A1 from TA when it was on sale! cheap! Less than $275.

Got my gun downgraded because it was shooting 407FPS. After the downgrade it was shooting 300, with a 110 or 100 spring (forgot). I was fine with it since I could use it indoor. Get to Ultimate Airsoft's Field, shoots 380FPS-390FPS.

THEN got it downgraded again to hopefully shoot less than 350FPS.

SO here is the actual problem. When they opened the gearbox again we found strings of debris in it. Didn't know what it was. Turns out if was the motor gear that was striping. Changed it but still doesn't work.

Factory Defect? or Generally Unlucky? Does anyone else with a KA M4A1 (licenced colt) have any problems with it at all?

Any input, stories or anything would be greatly appreciated!
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Old August 13th, 2012, 00:28   #2
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Join Date: Sep 2010
Location: Calgary, Alberta
By motor gear, do you mean pinion gear?
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Old August 13th, 2012, 01:11   #3
Join Date: Mar 2008
Location: Calgary
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The pinion gear is the one on the motor. The bevel gear is the one in the mechbox the pinion gear engages. My guess is the motor height was set improperly which caused either the pinion or the bevel gear to wear over time. This is probably why it still worked for some time. Does it just do nothing when you pull the trigger or does it make a grinding sound?

Are you sure the pinion gear was the one that was worn? In my experience the bevel gear strips much faster than the pinion but I have never owned a KA M4. It was likely not a factory defect. You'll need new gears and seeing as you've already replaced the pinion, the bevel would be the next one to try but in all honesty, just get yourself a complete set of quality gears from Modify and they'll last forever.
JG HK416
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Old August 13th, 2012, 02:19   #4
a.k.a. Greedy
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Join Date: Dec 2010
Location: Toronto
+1 sounds like your motor height was not set correctly. Make sure it is set properly now or you'll just wreck another gear. No need to get a new set of gears IMO if yours are still in good shape KA makes decent gears.

Make sure you're cronying with the same weight bb every time. If your FPS is inconsistent check your compression, a metal shard from your stripped gear could have wrecked an o ring. An M110 spring should put you at give or take 380 fps, M100 360ish FPS. It's possible the guy who changed your spring in the first place got a bad crony. You'd need a weak spring or a heavy bb to get 300 FPS unless your compression is bad.
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Old August 13th, 2012, 09:52   #5
a.k.a. Palucol
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Join Date: Mar 2008
Location: MTL
Here you go, this might help!

Airsoft Megastore TV - "How To" Motor-Height-Adjustment Video - G36/M4/AK47 - YouTube
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Old August 13th, 2012, 11:10   #6
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Join Date: Apr 2006
Location: Toronto
Need a bit more specific information....
As others have described there are a number of different gears, each with their own name. It'll help diagnose problems.

More to the point is "Changed it but still doesn't work" is the most important. What was changed?...and more description of what "doesn't work" is needed. Plain language laymans description is long as there's enough detail.

For example...there's a world of difference between...
"it shoots but makes a horrible whining sound"...and..."when I pull the trigger nothing happens"...and..."the gun cycles but no BB comes out"...etc...

Re. FPS...if you want to be sure that you're under 350fps with 0.20g BBs then stick to a 100% or M90 spring (a Modify S90+ is a good spring). In that mechbox it's likely to shoot 310-340fps. You'd still need to chrony to be sure.

Re. who's doing the upgrades/downgrades/ might want to find someone else to help you because any decent gun doc would have:
1) chronied the gun to tell you what it was shooting
2) picked an appropriate spring so it'd be in the right range
3) set the motor height properly and made sure it was going to stay there

Re. stuff breaking....happens all the time, sometimes suddenly. A good setup will simply last longer than a poorly assembled setup.
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Old August 14th, 2012, 10:19   #7
Join Date: Jul 2012
i think you should trade it
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Old August 14th, 2012, 19:07   #8
IroningMan's Avatar
Join Date: Apr 2012
Location: Toronto
They chrono-ed before hand and got 407fps (MAX) then after the spring change it was 300FPS range. They just tried the spring that was one level lower.

It was the gear attached to the motor that was stripping. Also another problem was the seal. They tried adjusting the motor height but nothing worked (clock/counterclock). There was no sound in either case.

In any case to fix everything so that it works (probably) would take just under $200.
As the guy said, just going to trade in.

Thanks for your input! I hope no one else will have problems with their King Arms M4 but if they do, I hope the post here will help!
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Old January 26th, 2021, 17:08   #9
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Join Date: Oct 2007
Location: Cranbrook, BC
Sorry for the unrelated post...

Jhhoo, your inbox is full, I can't send you a message untill it gets cleared out a bit...
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