King03sh Posted November 24, 2017 Share Posted November 24, 2017 Hey guys, im having an issue with my king arms m4a1 I hope someone can help with. I brought my aeg new with an advertised fps of 350-370, I installed an m100 spring so I knew it would be field legal for my first game (dont have access to a chrono) whilst doing a few mods/upgrades inc radius gb, aoe and metal bb spring guide, this ran fine on 8.4v battery for the whole day but was a little disappointing at only 250fps on .20s. Subsequently I have reinstalled the oem spring but now it will not run on 8.4 nimh and drains a fully charged 9.6v nimh in 40 rounds. The battery is brand new so should not be faulty as is the motor (no identifying marks on motor), is it possible the standard motor is unable to cope with the increased pressure from the bb spring guide? Or is the battery likely the issue? Ps if an 8.4 nimh is installed it will not rotate the gears at all and the battery gets rather hot, there are no issues in the gear train, all move freely and are correctly shimmed. Any help much appreciated. Thanks Link to comment Share on other sites More sharing options...
Supporters Samurai Posted November 24, 2017 Supporters Share Posted November 24, 2017 Really bad shimming and/or motor height is my first guess. KA guns are really nice both internally and externally. You tried to fix it. Link to comment Share on other sites More sharing options...
King03sh Posted November 24, 2017 Author Share Posted November 24, 2017 Shimming and motor hight is spot on, I've tried the original spring and guide n it runs flawlessly, the m100 n bb spring guide works fine, just issues with the m110 and bb guide, im guessing the extra compression from the bb guide is to much for the motor to overcome or the battery is naff but thats just an educated guess at this point, dont have funds available to change both motor and battery atm so hope someone may have a better idea than me. Quality of the gun is really good apart from the faulty cut off lever out the box, just gutted its out of action again atm Link to comment Share on other sites More sharing options...
Hangtight Posted November 24, 2017 Share Posted November 24, 2017 If you only got 250fps on a M100, there's your first problem. You have a poor air seal somewhere. Trying to compensate for that with a stronger spring isn't going to help matters. If the battery is getting hot when it wasn't before then it is being overloaded, either by electrical resistance or mechanical load. A bearing spring guide is superfluous if the piston has a bearing. You should have more headroom than you appear to have for fitting a heavier spring. I suspect the shimming and motor height are a little less than 'flawless'. Has angle of engagement been sorted? Link to comment Share on other sites More sharing options...
King03sh Posted November 25, 2017 Author Share Posted November 25, 2017 Iv spent a few hours shimming the gearbox and the motor is right in the middle of the sweet spot so Im quite confident thats not the issue, I do have an air leak from the air nozzle but have a double o ring ready to fit, cylinder head and piston seal really well. I am aware tho that my cylinder is a type 0 on a 363mm barrel so think over voluming is part to blame for the low fps Link to comment Share on other sites More sharing options...
Hangtight Posted November 25, 2017 Share Posted November 25, 2017 Type 0 on a 363mm barrel with 0.28g BBs is about spot on. How tight is the O ring in the cylinder? How are you measuring your 'sweet spot'? Current meter? Link to comment Share on other sites More sharing options...
King03sh Posted November 25, 2017 Author Share Posted November 25, 2017 Im using .20s at the moment n getting 250fps, o ring seals nicely, gives good compression but moves freely in the bore. Iv not measured the current tbf, just listened to the noise of the gun whilst adjusting the motor, where do you measure across and what procedure do you use? Iv not heard of current meter being used to adjust motor height before Link to comment Share on other sites More sharing options...
Hangtight Posted November 25, 2017 Share Posted November 25, 2017 https://www.ebay.co.uk/itm/60V-100A-DC-RC-Helicopter-Airplane-Battery-Power-Analyzer-Watt-Meter-Balancer-R-/112564720007 Or anything similar. It just goes inline between battery and gun. have you checked the air seal at the hop? Turn the gun upside down and place a small piece of paper over the feed tube in the magwell. When you fire the gun it shouldn't move. Have you checked that the piston is free to run on its rails when the gearbox is screwed closed? That the guide is fully seated and not jamming the piston? Link to comment Share on other sites More sharing options...
King03sh Posted November 25, 2017 Author Share Posted November 25, 2017 Thanks for the link, I shall get one asap, I hadnt come across this way of testing the hop for leaks, il give it a go when I get home n update you. Piston seems to move freely on the rails and the guide is definitely seated correctly, I will double check everything again when I split the box just to be sure, probably something really basic im not doing right lol, its the first gun iv tech'd on so a bit of a learning curve Link to comment Share on other sites More sharing options...
Supporters jcheeseright Posted November 25, 2017 Supporters Share Posted November 25, 2017 First gun you've ever done, yet the shimming and motor height definitely aren't to blame for it nailing a whole battery in 40 shots? its either the shimming or the motor height, also, don't bother using an M110 to compensate for poor air seal, you should be able to get 300+ with an M90. Sort the air seal first, use a weaker spring and double check (or have someone competent check for you) the shimming. Link to comment Share on other sites More sharing options...
King03sh Posted November 25, 2017 Author Share Posted November 25, 2017 I understand you scepticism, however im no foolhardy over enthusiastic teenager with a screwdriver, I have spent a long time learning each process before I attempt it with a logical and methodical approach, I shimmed the height of my bevel gear to the pinion, then each gear from there on, each has approx 0.7mm lateral movement and good clearance between each gear. My shim job has been checked by a much more experienced tech than me and given the thumbs up so im quite confident I did a good job, motor hight is a possibility but again it fired well with the downgraded spring hence my current confusion... im open to the suggestion I made a mistake somewhere but trust my friends assessment that it was satisfactory. Il be sorting the air seal tonight hopefully with an shs double ring nozzle n checking the hop unit, will of course double check my other work again n see if I can find any other issues Link to comment Share on other sites More sharing options...
King03sh Posted December 18, 2017 Author Share Posted December 18, 2017 Thanks for everyone's replies. Iv had my gun looked at by someone more knowledgeable then me, the issue was the motor. Have swapped to a jbu high torque and solved the problem. My friend also swapped out the gear set for a 12:1 combination of shs and g&g gears, and changed the piston and head for prometheus blue items, shes running beautifully and I look forward to playing with it soon. Also the air leak was coming from the hop chamber, iv whipped the bucking with dental floss and its significantly improved. Now to move on to barrel and hop upgrades :-) Link to comment Share on other sites More sharing options...
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