Compression issues

[kaponk]

As some of you may remember, i had a malfunctioning A&K Mk43 Mod 0 LMG, since that older post I have personally fixed it, had a shop fix it, and now I have pin pointed the main reason for my bbs not firing right. The compression is far from good, it pushes in with little to no resistance, i have wiped out all the grease and other stuff that had gotten into the cylinder sleeve and even wiped the O-ring down. Also noticed it doesnt really compress till about, actually over half, way into the sleeve. Now I know there are mods for this, but couldnt find any using search and google. Does anyone have an idea of how to fix this?

[ctres]

You will need to determine where the air leak is occuring. I'm not sure what you mean by the sleeve, but there are several places that could potentially cause air leaks in the gearbox.
1. Piston head O ring. Can be replaced with a #14 or dash #116 I believe from McMaster
2. Cylinder head o ring I think I'm the product of two siblings sleeping together.. doy! on the o ring size, but it can easily be sealed with teflon tape
3. nozzle to cylinder head o ring (or lack thereof if it is stock) which can be fixed with an upgraded nozzle, although I don't know for sure what type the m60 uses.

Most likely you will just need to swap out the o ring on the piston head. I would reccomend part #9263K247 at www.mcmaster.com/#
As well as some 10 weight rc silicon shock oil.

[TheEnd]

Dec 5, 2011 16:36:53 GMT -5 kaponk said:

....I have wiped out all the grease and other stuff that had gotten into the cylinder sleeve and even wiped the O-ring down.

Did you remove all the lube from the cylinder? If so, that is going to kill your compression. The cylinder is supposed to have lube in it to help the O ring seal. When you test your compression are you putting your finger over the cylinder head brass nozzle, or your plastic nozzle? As ctres said if your plastic nozzle has no O ring it won't seal very well.

Why do you think you have a compression problem?

[kaponk]

Yes, I made sure to take the plastic tip off and test it, i tested it before doing all that I said, and the compression was awful. I think I have a compression problem, cause my gear box is now working fine, the bucking is in great shape, yet when I fire, the bb`s will just go everywhere, some go so so distance others just kinda fly out and go randomly, needless to say from this random firing makes the gun not usable cause it barely shoots to 20ft. When I first got it and it worked, it was a nice straight line. If it will help I can make a video to show the random firing i`m talking about.

[kaponk]

Sorry for the double post, seen I missed a question, yes the plastic nozzle has no o-ring and i am going to crack the gear box back open, re-lube the cylinder, but even lubed the bbs dont go far. I am going to look into getting different o-ring. Also, I know this will sound stupid, but as I push down, the air simply, i can feel it, goes out the back of the cylinder, it has compression, but as I said, it`s very bad and I think is my issue for the bbs not going far.

[TheEnd]

There is an "edit post" button in the top right corner if you need to edit your previous post.

Most times clone AEG piston O rings are pretty crappy. It would be wise to swap out your O ring. It is also important to make sure to lube the cylinder properly. When you checked your compression did you force the piston in or slowly push it in? You have to force it in like the spring would or else the O ring won't work.

I'm pretty sure the A&K MK43 uses the same hop up as the M249. Do you know about the nub problem that hop up has? The nub is cut too short and doesn't actually apply any hop. It's possible your issue is in the hop up and not actually a compression issue. Try searching "A&K M249 hop up fix" on Google and you should find plenty of fixes.

[kaponk]

Thanks for that, and I was just sliding it in, thanks for the info about that, and i`ve heard of hop-up possibly being an issue, just didnt think the hop up would make the bbs come out and some drop just like a foot or two infront of me. I`m defiantly going to look into a new o-ring cause the one in it now is very loose, also I just re-lubed it and but some teflon tape around the, sorry for my poor terminology, but the nozzle, piece that slips into the opposite end of the cylinder, has the nozzle on it, and i felt like it has more compression as is, but still want to get a better o-ring and defiantly will look into the hop-up. I can`t test fire, due to it being night, but i will try tomorrow and see if it is any better.

[TheEnd]

It sounds like you have a minor compression issue, and also a mechanical issue. I would recommend you pick up a #14 O ring. You can find them at a hardware or auto parts store, or order one with the number ctres posted. That should fix your compression issue. Use a quality silicone oil to lube the cylinder, not white lithium.

Even if you removed your O ring completely your bb's should go beyond a couple of feet (don't actually try it. It's bad for everything). I think your hop up has a problem. My A&K M249 had a hop up bucking without a sealing lip. The nozzle just rammed into it to create the seal. I would take a close look at your bucking and see if it is as loose on the barrel as mine was. If it is the flat faced type replace it with one that has a sealing lip. After replacing my bucking and sealing it to the barrel I picked up 40 fps.

Also make sure your barrel is clean. A dirty barrel can do some terrible things to range and accuracy.

[Grimm(3.14)]

To me, it sounds like if you've done the compression tests with your cylinder and piston and had the test pass, then I would say your hop up is at fault.

Even though I don't have the type of rifle the thread is about I just had a similar experience with my TM m4. I had my nozzle and gearbox shell break, replaced all said parts, and then was having some sort of compression issue. My m4 was only shooting roughly 100 fps and going maybe 10-15 feet. After taking everything back apart, regreasing and reshimming, compression test after test, I finally replaced the hop up completely (bucking and all). Once it was back together, no more compression issues. Come to find out, the previous hop up I purchased was not compatible with mine.

Id recommend re-checking the compatibility of the hopup or if it is possibly cracked somewhere, before purchasing expensive parts. Just my two cents for you! Good luck, and hopefully this helps!

Sent from my DROID2 using ProBoards

[kaponk]

Thanks, well i`m at my wits end and might just be selling the gun, I know I wont get much, but the gear box repeatedly locks up, already sent it to a shop, they fixed it ,but even when it was working it still fired weird. Actually the day I got it back, the spring guide blew out the back and I had to push it back in only to have the gear box lock back up. So i`m gonig to more then likely just sell it as is, i`m sick of this issue, no idea why the gear box keeps locking up and apparently even the mechanics don`t know. Thanks for all the help, but I truly just think this is a complete mess, no way i`m buying a new gearbox only to have the same risk of another big mess.

[TheEnd]

Are you located in Michigan? If you are there are a few shops around the state that should be able to fix it for you. The SAW box is very simple and it shouldn't cost you much to have it fixed.

What shop did you send it to?

[kaponk]

No, i`m in Kentucky, and sent it to the closest one, Nashville airsoft, but when I took it there, it fired, didnt have the screws that held the gear box in the gun in, and they said that was the issue, but I argued it didnt fire and locked up even with screws holding it in place. I think they didnt do all that I asked and simply said it was that, needless to say they wont be repairing any of my guns anymore. I have just reopened my gear box, adjusted the shims a little on some of my gears and adjusted the motor height and the compression, when doing it as The_End said, it does seem better, going to take pictures of my hop-up to let you guys see, i`m pretty sure the hop-up is different from that of the m249.

[TheEnd]

Sometimes people list their hometown as their location while they are here at school or something, so I thought I would ask.

When you say it fires weird, what do you mean? The trigger switch in the A&K SAW box is known to have a few issues. Do you have a lot of rounds through it? What kind of battery are you using? My A&K motor burned out really fast. It became really weak and loud, and then one day started smoking.

So now we are up to 3 issues.

- Possible compression issue
- No range
- Fires weird (needs explanation)

Rather than sell it at a loss, take a break from it. Leave it be for a day or two and then get back to it. It might seem like everything is going wrong, but it's fixable.

If you are ready to trouble shoot, it's best to tackle issues one system at a time. I think the best way to approach this is to get the gear box firing correctly. Fixing anything else won't matter if your gearbox isn't working right because you can't test it reliably.

Explain what you mean when it's firing weird.

[kaponk]

Alright, sorry, what I mean by firing weird is the same by no range, the bbs just spit out randomly.

Now as far as my gearbox issue, it`s beyond me, cause i`ve reshimmed and done everything possible without replacing anything and it still locks up. I`m starting to think it`s the motor.

[TheEnd]

It could be your motor. Try taking the motor out of the box and push the switch. See if it sounds normal or sputters or anything. If you have a spare motor swap it in and see what happens. I wouldn't be surprised if it is the motor.

It could also be the spring is overpowering the drive train, the shims are too tight, or the switch is bad. After a while the contacts in the switch corrode and begin to fail.