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Spinxtercell

Compression and range problems after repair AEG

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I have a JLS Beretta RX-4 Storm (M14 version 7 gearbox style), the piston broke after two years of good performance. The pistons metal tooth broke and scuffed up my cylinder so I replaced the cylinder with a G&G one and the piston with a TM or Classic army not sure. The stock spring wore out thanks to anti-lock up so I put a G&G F2000 spare stock stiff spring in and it still wont penetrate cardboard! The range is poor and drops after about 20 yards or a half inch below what ever I aimed at. The compression feels strong if you dry fire on your hand. Adjusting the hop does nothing for accuracy and range. If it helps I have a 11.1v 1600mAH Li-Po with Deans plugs and I was doing these tests in semi. I need recommendations for compression parts for a Ver. 7 gearbox, or a fix to my compression/range issue.

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Edited by Spinxtercell

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Check and make sure the cylinder port is facing the right way( if there is one) and make sure your cylinder head is still ok. Put your finger over the nozzle and press the piston down into the cylinder. Should let you see if you have good compression or not. Just dry firing won't tell you much

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Check and make sure the cylinder port is facing the right way( if there is one) and make sure your cylinder head is still ok. Put your finger over the nozzle and press the piston down into the cylinder. Should let you see if you have good compression or not. Just dry firing won't tell you much

My cylinder did take some damage when the piston broke and I ordered ASG Ver. 7 cylinder head that didn't fit (P.S. that cylinder head is for sale if you want it.) while I had it open I tested the compression like you said before I put the gun back together with the assorted parts, it had okay compression as far as I could tell. The G&G spring I put in could have been worn out to since it was replaced in the F2000, I hope its as simple as that. Thanks for the advice!

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I put around 100k rounds through my old g&g plastica and never had a range drop off like that or even have a spring wear out. Something else probably got messed up when that tooth broke. I HIGHLY doubt your issue is spring caused. I would keep checking your compression parts and even your hop up unit. Even with bad compression your hop up u it should add a little more range if you over hop it

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Agreed, Check the porting, how long is your barrel?

I've never really used an FN2000, but if I had to guess, being bullpup, the length should be similiar to an AUG, So 400-500mm?

 

At that point you need a 3/4th cylinder, or even a 4/5ths cylinder.

~~~

 

How I test my compression is taking out the cylinder, put the cylinder head, piston assembly, and air nozzle in, then plug the air nozzle witrh your finger and push the piston back and fourth, it should stop once it passes the cylinder porting hole.

 

The faster you press the piston in, the better the seal, due to the piston head porting design allows the o-ring to expand.

~~~

 

Lastly, once thats all in, I dry fire with my finger at the end of the barrel, and check the hopup chamber if air flows downward [meaning air is redirected down into the feeding tube, and not into the barrel. Some air is fine, a lot no...

 

I also do this test where I put 3-4 BBs down the magwell hopup, have the gun upside down and fire. If the BBs jump from the magwell a few inches, its 'generally' okay and I consider it acceptable-good compression. If they fly to your ceiling/fly a couple feet up in the air, thats horrible compression!

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aw man, wish I had one of those jls storms

 

if your cylinder isnt in there wrong then id check the o-ring on the piston head to make sure its not too hard or too small

give that cylinder head a good check. see if its metal tube is loose or if its o-ring is worn out

 

might also be something with your air nozzle or the hop up. make sure your hop up is close enough to the gearbox

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Agreed, Check the porting, how long is your barrel?

I've never really used an FN2000, but if I had to guess, being bullpup, the length should be similiar to an AUG, So 400-500mm?

 

At that point you need a 3/4th cylinder, or even a 4/5ths cylinder.

~~~

 

How I test my compression is taking out the cylinder, put the cylinder head, piston assembly, and air nozzle in, then plug the air nozzle witrh your finger and push the piston back and fourth, it should stop once it passes the cylinder porting hole.

 

The faster you press the piston in, the better the seal, due to the piston head porting design allows the o-ring to expand.

~~~

 

Lastly, once thats all in, I dry fire with my finger at the end of the barrel, and check the hopup chamber if air flows downward [meaning air is redirected down into the feeding tube, and not into the barrel. Some air is fine, a lot no...

 

I also do this test where I put 3-4 BBs down the magwell hopup, have the gun upside down and fire. If the BBs jump from the magwell a few inches, its 'generally' okay and I consider it acceptable-good compression. If they fly to your ceiling/fly a couple feet up in the air, thats horrible compression!

 

Well the F2000 barrel in my gun only extends by a few inches nothing much, my cylinder is G&G GR16 EBB with one small hole on the top for the blowback. With the hole facing the cylinder head I get terrible compression with BB's falling very short, I put electrical tape over it and the BB's started to fly a lot farther but its still just to weak and can't reach most engagement distances. I did try testing the finger over the nozzle and it seemed fine. I'll check out the feeding tube test.

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you NEED to get rid of that blowback cylinder duh.

or if it has no side porting flip the cylinder so the hole is in the back. .....you cant just put tape over it

That's the thing if I were to flip the hole to the back there's a notch cutout that would be touching the cylinder head.

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The hole even if blocked will lose compression. The problem is the o-ring cannot form to it very well as it passes. FPS loss? Not sure but I can tell you it does that. You need some tech advice on checking compression?

After some time up to last night I opened it up and tested for compression with two different cylinders, the G&G blowback one worked the best. I turned it around as advised by someone on the thread (I Apologize I don't remember who) and it was the same until I put a lose fitting O-ring on the piston head and man was it good, really hard to push the piston down while covering the nozzle. So at this point the compression is looking good and the spring is way to long for this gearbox and way to stiff so its pushing that piston even with all the compression. I assemble it (the whole process takes over an hour, its a really :censored2: to work on) and take it out in the Moring to see that it does the same thing! I'm going to test a different hop rubber later today but what are your thoughts on this?

 

 

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you NEED to get rid of that blowback cylinder duh.

or if it has no side porting flip the cylinder so the hole is in the back. .....you cant just put tape over it

I'm telling several people on this thread what happened. After some time up to last night I opened it up and tested for compression with two different cylinders, the G&G blowback one worked the best. I turned it around as advised by someone on the thread (I Apologize I don't remember who) and it was the same until I put a lose fitting O-ring on the piston head and man was it good, really hard to push the piston down while covering the nozzle. So at this point the compression is looking good and the spring is way to long for this gearbox and way to stiff so its pushing that piston even with all the compression. I assemble it (the whole process takes over an hour, its a really :censored2: to work on) and take it out in the Moring to see that it does the same thing! When I came back inside I put a BB in the feed tube and covered the end of the barrel and the BB shot up to the celling. I'm going to test a different hop rubber later today but what are your thoughts on this?

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Agreed, Check the porting, how long is your barrel?

I've never really used an FN2000, but if I had to guess, being bullpup, the length should be similiar to an AUG, So 400-500mm?

 

At that point you need a 3/4th cylinder, or even a 4/5ths cylinder.

~~~

 

How I test my compression is taking out the cylinder, put the cylinder head, piston assembly, and air nozzle in, then plug the air nozzle witrh your finger and push the piston back and fourth, it should stop once it passes the cylinder porting hole.

 

The faster you press the piston in, the better the seal, due to the piston head porting design allows the o-ring to expand.

~~~

 

Lastly, once thats all in, I dry fire with my finger at the end of the barrel, and check the hopup chamber if air flows downward [meaning air is redirected down into the feeding tube, and not into the barrel. Some air is fine, a lot no...

 

I also do this test where I put 3-4 BBs down the magwell hopup, have the gun upside down and fire. If the BBs jump from the magwell a few inches, its 'generally' okay and I consider it acceptable-good compression. If they fly to your ceiling/fly a couple feet up in the air, thats horrible compression!

I did the test you were talking about after getting good compression like you said. It stopped after the port which I switched around to face the back, 1 BB in the feed tube and finger over the barrel and the BB shot up to the ceiling.

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