zephurah
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Post by zephurah on Oct 14, 2014 17:47:15 GMT -5
I'm no idiot when it comes to teching, I know what I'm doing. However, this case is extremely difficult to figure out from my perspective.
Here's the story, I bought a PTS Masada SV from airsoft Atlanta. Upon opening it, and shooting it for the first time, it was fine. It fed decently, and had the correct amount of range and accuracy. However, the gears were loud, and the engagement was not exactly that good. I corrected AoE, (sorry cam), I re-shimmed, and finally bought a new bucking, barrel etc. Not up until recently have I had issues with it feeding. It started happening right around the time I painted the gun. After that happened it magically decided to not want to feed in any way. So I took a look at the paint around it, no visible issues. To be sure, I filed the paint off of the hop-up area. Keep in mind that this gun has a two piece hopup. This did not really change anything at all.
Only recently did I make some small adjustments. I switched the sorbo pad on the cylinder head, lubed the gearbox with white lithium grease, and switched around the shims for correct bevel to pinion. The last change I did was to stretch my tappet plate spring just a tiny bit. My thinking was that if the tappet plate required less force to pull it from the sector gear, then maybe it would be able to pull backwards more. Now for a while, that fixed my feeding issues. However, my fps dropped to maybe 5. Thus making me think that I had caused an air leak when taking the replica apart.
So I re-open it, for maybe the 3rd time in a week... looking at my piston and observing what could have happened. I tested the compression, which was solid, I pushed the piston in, and I got a good amount of feedback. It was possible to push it through to the cylinder head, however. So I checked that off my list.
But now i'm completely stuck, as I tried shoving a BB into a standard M4 one peice hop-up and barrel I have. I put this on the nozzle, and it shot at perfect FPS. So I can't tell whether I should be looking at my hop-up, gearbox, or both.
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Post by Squirrel on Oct 14, 2014 18:50:48 GMT -5
Stretching the tappet spring doesn't seem like the greatest of ideas. Regardless of tension, it should go full cycle back because the post on the sector gear has to pull the tappet full back in the gears cycle. Stretching this spring will only hinder the forward return of the tappet and air nozzle.
The new bucking you put in would be the change that comes to mind that would effect your feeding and FPS. Was it a harder bucking you put in? Did you check to see if the lips of the bucking are protruding into the hopup chamber, hampering your feeding?
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zephurah
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Post by zephurah on Oct 14, 2014 19:17:17 GMT -5
Consider the bucking a non-factor, as it was installed way before these problems started occurring.
But how would stretching the tappet spring, even the smallest amount, affect FPS?
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Post by Squirrel on Oct 14, 2014 19:33:50 GMT -5
Like I said, it could theoretically slow the forward return of the air nozzle. If you do not have a solid bucking to nozzle seal at the moment after the piston is released forward, your FPS can drop. Also, your nozzle may not be moving forward with sufficient velocity to seat a bb before the puff of air comes. Theoretically this could also be what is causing the feed issue.
Now, there could be other factors here, but as stretching the tappet spring doesn't seem like a common thing to do, I wouldn't rule it out as a possible problem.
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zephurah
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Post by zephurah on Oct 14, 2014 19:42:43 GMT -5
You are probably right, however I'm not sure that is the cause of the feeding issue. When I look in the feeding tube, the bb is resting below the nozzle. It wont push through the nozzle into the hop-up chamber, unless forced.
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Post by Squirrel on Oct 14, 2014 19:55:45 GMT -5
That is a strange issue. So are you saying the BB doesn't make it past the lower half of the 2 piece hopup?
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Post by Deacon on Oct 14, 2014 20:29:15 GMT -5
Stretching the tappet plate spring would affect feeding by not allowing the nozzle to fully return and seat in the hop up rubber correctly. Have you inspected the bucking for excess lube from the lube job?
If your Compression is fine but is not fine when firing.. check the meshing between the upper hop section and the gearbox. The springs are notoriously weak and bounce away from the gearbox often.
It also just occured to me that you said you can press the piston fully against the cylinder head. Are you getting no resistance with your finger blocking the nozzle? In all of my builds I get just passed the port and my piston wants to pop my cylinder heads out of the cylinder.
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T6e9a
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Back in business
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Post by T6e9a on Oct 14, 2014 22:33:22 GMT -5
Make sure screws that secure the hop up unit in are all fine, and that the upper hop up and lower hop up align well.
I would check to make sure there isn't anything jamming the tappet plate from going all the way back. This is probably a given, but make sure the air nozzle is properly mounted on the tappet plate.
Also, make sure the airnozzle can go all the forward and backward on the cylinder head without too much friction.
And either shorten your tappet plate spring a little, or replace it with a stock one. Stretching did it no good.
Also, a general rule for PTS masadas(not A&K) is when ever you take out the barrel, ALWAYS make sure the hop up is all the way off, otherwise you can potentially ruin the bucking, or nub, or both.
Also, something else to try if resources permit, is try putting a sector chip in, and see if that might help it any.
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zephurah
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Post by zephurah on Oct 15, 2014 12:36:34 GMT -5
To answer all questions,
Squirrel: The bb occasionally makes it through, but it does not often happen.
Deacon: The bucking does not have excess lube on it. The cylinder does offer resistance when pushed forward, but the compression does not block the piston from moving forward. Therefore it is possible to push the piston all the way through to the cylinder head. Also, there is not really a way to change the meshing of the lower and upper, as it swings on like a real AR-15.
T9e6a: I checked the tappet plate when the gearbox was assembled, and it seemed like it was fully able to move forward and backward. I lubed the air nozzle just slightly, so it does not have much friction there. I may have to replace my tappet plate spring after doing that, so that may be a factor. Finally, there is currently a sector chip inside of the gearbox. And yes, I make sure to check that my hop-up is always off when removing the barrel (Madbull 363mm x 6.03mm)
One final thing, the reason I stretched my tappet plate spring was because I saw that the tappet plate was easily bendable. Leading me to believe that it was bending out of the way of the sector gear, and sector chip. This may be due to the way that the gearbox is shaped.
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Post by Deacon on Oct 15, 2014 15:20:01 GMT -5
I was speaking about the gearbox and upper section of the hop up unit not meshing properly. What frequently happens is the spring attached to the upper hop up section is weak and will allow movement away from the gearbox. When this happens a space is created between the hop up, the air nozzle and the gearbox which generally results in poor compression and feeding.
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zephurah
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Not sure how I feel about my status.
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Post by zephurah on Oct 15, 2014 17:19:41 GMT -5
There is no spring on the upper part of the hop-up. Keep in mind, this is not a normal two piece hop-up. I can post pictures on request.
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Post by Deacon on Oct 15, 2014 17:28:23 GMT -5
So there's no spring sleeved over the barrel to put pressure against the gearbox like this:
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zephurah
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Not sure how I feel about my status.
Posts: 187
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Post by zephurah on Oct 15, 2014 17:59:41 GMT -5
Oh, no there is. I thought you were talking about the spring that is usually on a normal M4 hop-up.
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Roger Monk
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Post by Roger Monk on Oct 15, 2014 19:13:01 GMT -5
When you just stated that your tappet plate is easily bendable, that set off a lot of red flags for me. I had a similar feeding issue and the tappet plate and spring were my main problems. I would suggest putting in a new tappet plate and spring. You say it will occasionally feed a bb witch is probably the occasional time where the tapped plate goes fully back. Look for up and down bend in the tappet, if it's very easy to do this then I would invest in a new SHS tappet play witch should only be $8.
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Post by Stinger on Oct 15, 2014 21:07:55 GMT -5
Check to make sure it isn't your magazines pushing on your hop-up in any weird way. I say this because I have spent the last three months changing out all kinds of parts in my M4, only to find that the issue all along was that my magazines had worn down and weren't fitting right anymore.
If you can, follow a basic troubleshooting technique: Isolate the problem to one area of the gun. Identify problem. Figure out how it needs to be fixed.
Also, make sure that the compression in the gearbox is good: Take the cylinder, cylinder head, air nozzle/tappet plate, and piston out. Assemble them together, and then cover the air nozzle opening with your finger. Pull the piston out, then thrust it into the cylinder like it would while firing. If air leaks out, you have a bad seal. The piston should resist your pushing.
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