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> Correcting Angle of Engagement (Necro Exempt), Also known as AoE
Star_folder
post Jun 12 2011, 11:09 PM
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Alright, so remember that M4 that I showed you guys how to Pop the ARL? Well, it's not working, so it's still my guinea pig, and now I'm going to show you guys what AoE is.

I know there are many, many guides on how to adjust and correct the AoE, some are probably a good bit better, but this is just my go at it.


We're going to say you can get to this point from one of the Numerous guides on how to take apart a gun, in this case, an M4. Now, what's nice about AoE is that it can be adjusted in any gearbox, not just M4s. Every gearbox has a piston/gears and this mod will work for every gearbox.


Alright, the picture isn't all that great, but it's good enough to see what I'm talking about. That first tooth on the Sector Gear, the on at the top, see how it is hitting the first tooth on the piston, the really big one on the left? This is called improper Angle of Engagement, or AoE.

Think of it like a knife, the reason knives cut stuff is because they come to a point, and all that pressure is applied at the point of the blade. If you try and cut with the wrong side of a knife, it won'tg cut because it's not sharp, and the pressure is spread out. The same principle applies with AoE, just backwards. Because the gear is engaging the piston at a point, it will wear down that tooth until it just can't grab it any more. Adjusting the AoE is where you make the first tooth of the gear line up evenly with the first tooth of the piston. You spread out the pressure along the whole tooth, instead of that small point.


This is a picture of the damage that bad AoE can do to a piston.


This is what it should look like, or about what it should look like. It's not quite perfect, but it has been adjusted. Perfect AoE will have the first tooth of the Sector Gear lined up and parallel with with the first tooth of the Piston. If you notice, it's a little off. Now, this is still better from the first example, but not perfect. I left it as is, because this M4 is a loaner shooting 320fps in a stock gun, not very challenging at all.

Now, to push the piston back, you'll need a spacer of some sort to allow for the piston teeth to mesh correctly with the Sector Gear teeth. I used the stock rubber padding and some mouse pad foam to allow me to achieve the proper spacing.


Here's my mouse pad, I've already used it a few times, obviously.

I start by taking the cylinder of the gun and pressing it into the mouse pad. Pressing it hard enough to make an impression on the foam. Like this:




Then I cut the circle out of the foam.


Next, I use a hole puncher to put a hole in the center of the circle to allow for proper air flow into the air nozzle. The hole that you put into the padding at this step should end up being right over the air nozzle hole.


A picture of the foam pad over the cylinder head, note that you can easily see straight through the air nozzle.


Next, I remove the rubber padding out of the back of the cylinder head. It's kind of hard, and messy, but do-able. Just be sure you scrape out as much as you can and try to get the rubber pad off in one piece.


Next, you replace the rubber pad with the foam pad that we made earlier.

*note* It is a good idea to trim up the foam pad so that it fits better into the cylinder head.

For reference, this is the glue I use:


And now glue the rubber pad back onto the foam. The reason I do this is because the foam is soft and gets torn up very easily, the rubber pad helps to protect the foam so that it lasts longer.


A Side view:


The padding needs to be just right so that the first tooth of the piston and the first tooth of the Sector Gear are parallel to each other, You need to test this with your spring in. Foam Compresses under pressure, what the angle of engagement is without the spring will be different from the angle with the spring. Be warned, and be careful, you can screw up a piston if you don't check to make sure it's correct.

Alright, now if you'll notice, after putting in the padding, when you try to turn the sector gear it will hit the second or third tooth on the piston instead of the first:


Simply remove them, I use a dremel now that I have one, but I used files before that.


And now you'll notice that it all meshes correctly, and when the sector gear turns, it comes into contact with the first tooth of the piston first, and not one of the other teeth.

That's how I adjust my AoE.

--------------------------------------------------------------
I realize several of these pictures are rather sub par, so I want to invite anyone who cares to to one up me and make a better guide. We'll probably post many different ones. There are many ways to adjust the AoE, this is just one way. It is also rather late for me, so, please, let me know if I have misspoken, or made some sort of critical error. Thanks guys.
--------------------------------------------------------------

An update, but this time using sorbo padding as an example. The process is very similar to the foam, except I find that sorbo is strong enough that it doesn't need the rubber pad to protect it.


This is what it looks like after about 30k rounds. Yes, it took a few tries to get the hole right in the middle of the padding. Ended up looking like some triforce knock-off, but it still works.


This is what the cylinder head looks like from the side. You can see the sorbo is glued right on top of the rubber padding. Just be sure it is cleaned of all grease to be sure that the glue will do it's job. It doesn't need to be perfectly cut, as long as it fills up most of the cylinder head, has a hole for the air port, and evenly fits into the cylinder, then you are golden.

This post has been edited by airborne101: Aug 12 2011, 10:23 AM


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The Jam
post Jun 12 2011, 11:17 PM
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This is from DisguisedEnemy on ASM. http://m.youtube.com/index?desktop_uri=%2F...h?v=fNo8Go0Gd5c

Should be helpful for those who need a video.


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Behave
post Jun 12 2011, 11:34 PM
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Great and simple to understand guide. Star you are a very innovated and helpful person. Im sure we all appreciate the information you give to us, especially to us newbies!
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Cardboard Box
post Jun 12 2011, 11:36 PM
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Once I get a new piston, I can put up a guide to correcting AoE and premature engagement using washers instead of foam/sorbo.
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soccer77
post Jun 12 2011, 11:39 PM
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Good use of photos and short/simple descriptions.

Its a great guide :) Keep up the good work for airsofters everywhere!


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a4andy
post Jun 13 2011, 12:03 AM
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I would also suggest putting the spring and spring guide in when you are adjusting your AoE because the sorbo/foam will compress causing the piston to be seated forward more, and that's how it will be when your gearbox is closed anyways.

This post has been edited by a4andy: Jun 13 2011, 12:04 AM


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Behave
post Jun 13 2011, 12:11 AM
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QUOTE (a4andy @ Jun 12 2011, 11:03 PM) *
I would also suggest putting the spring and spring guide in when you are adjusting your AoE because the sorbo/foam will compress causing the piston to be seated forward more, and that's how it will be when your gearbox is closed anyways.


He did mention that.
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a4andy
post Jun 13 2011, 12:13 AM
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QUOTE (Behave @ Jun 12 2011, 10:11 PM) *
He did mention that.


Whoops, just lightly skimmed it a-blushing.gif


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Star_folder
post Jun 13 2011, 06:07 AM
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QUOTE (a4andy @ Jun 13 2011, 01:13 AM) *
Whoops, just lightly skimmed it a-blushing.gif

But it's worth mentioning twice. :D

Thanks for all the support guys, I'm glad you like it.


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shlunka
post Jun 13 2011, 07:32 AM
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Very helpful guide, no wonder my M16 wasn't firing right. Also, a warning, be very careful with loctite, I was doing some reinforcement on my M16 and then, I put waaay too much on it, so, not thinking clearly and rushing to get it off, I removed it with my thumb. Problem was, loctite is nasty stuff, and it burnt through the first two layers of my skin, I then had to remove it with a knife, which hurt A LOT since I had to cut below it to get it off, and that meant going through that last layer of skin, ouch.


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Star_folder
post Jun 13 2011, 07:58 AM
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QUOTE (shlunka @ Jun 13 2011, 08:32 AM) *
Very helpful guide, no wonder my M16 wasn't firing right. Also, a warning, be very careful with loctite, I was doing some reinforcement on my M16 and then, I put waaay too much on it, so, not thinking clearly and rushing to get it off, I removed it with my thumb. Problem was, loctite is nasty stuff, and it burnt through the first two layers of my skin, I then had to remove it with a knife, which hurt A LOT since I had to cut below it to get it off, and that meant going through that last layer of skin, ouch.

yeah, this stuff is crazy powerful, you really don't need much to glue the foam onto the cylinder head. I've glued my fingers together many times, or given them coatings of glue. I would use my dremel to remove the glue from my finger, isn't as painful, but if you aren't careful, you can hurt yourself.


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shlunka
post Jun 13 2011, 08:01 AM
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QUOTE (Star_folder @ Jun 13 2011, 08:58 AM) *
yeah, this stuff is crazy powerful, you really don't need much to glue the foam onto the cylinder head. I've glued my fingers together many times, or given them coatings of glue. I would use my dremel to remove the glue from my finger, isn't as painful, but if you aren't careful, you can hurt yourself.

Ahh, I used a hunting knife. I accidently squeezed it too hard. Also, how does this hold up to the constant impact of the piston?


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Star_folder
post Jun 13 2011, 08:14 AM
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QUOTE (shlunka @ Jun 13 2011, 09:01 AM) *
Ahh, I used a hunting knife. I accidently squeezed it too hard. Also, how does this hold up to the constant impact of the piston?

Good point, thanks for bringing that up.

The mouse pad foam doesn't hold up very well for very long. That is why you glue the rubber pad over it, as it helps it last longer. I suggest the use of Sorbo, as it is much more resilient than this mouse pad foam.


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shlunka
post Jun 13 2011, 08:23 AM
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QUOTE (Star_folder @ Jun 13 2011, 09:14 AM) *
Good point, thanks for bringing that up.

The mouse pad foam doesn't hold up very well for very long. That is why you glue the rubber pad over it, as it helps it last longer. I suggest the use of Sorbo, as it is much more resilient than this mouse pad foam.
Where do I get sorbo?


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Star_folder
post Jun 13 2011, 08:48 AM
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QUOTE (shlunka @ Jun 13 2011, 09:23 AM) *
Where do I get sorbo?

I get it from McMaster-Carr.

The column on the left of the screen has the info in it, just pick the duro that you want and how many sheets you want, and click add to order. The higher the Duro rating, the harder the sorbo. Personally, I use 70D in all my guns.


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thatguyx
post Jun 21 2011, 08:59 AM
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What are the pros and cons of correcting AoE via padding the cylinder head vs adding spacers to the piston?

From what I can tell, padding the CH will alleviate stress on the gearbox and maybe change the sound but at the cost of less cylinder volume ie a small drop in fps. If using spacers there maybe be a tiny drop in RPS if the spacers are heavy and it doesn't provide the cushioning of padding the CH.

Anything else I'm missing?
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Age
post Jun 21 2011, 09:26 AM
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QUOTE (thatguyx @ Jun 21 2011, 09:59 AM) *
What are the pros and cons of correcting AoE via padding the cylinder head vs adding spacers to the piston?

From what I can tell, padding the CH will alleviate stress on the gearbox and maybe change the sound but at the cost of less cylinder volume ie a small drop in fps. If using spacers there maybe be a tiny drop in RPS if the spacers are heavy and it doesn't provide the cushioning of padding the CH.

Anything else I'm missing?


Using spacers will also decrease cylinder volume. There is no difference between using spacers on the piston head or adding a buffer to the cylinder head...Except that adding a buffer will reduce stress, so the buffer is more beneficial.


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EDI 1st
post Jun 21 2011, 12:42 PM
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Question about filing down the teeth...
Any suggestion if they are made out of Stainless Steel(?)

It's this one http://www.airsoftpost.com/product_info.ph...oducts_id=30841

Or should I just put the stock CA-25 piston back....

Running on brand new Guarder SP170...

This post has been edited by EDI 1st: Jun 21 2011, 12:42 PM


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Cardboard Box
post Jun 21 2011, 12:50 PM
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QUOTE (Age @ Jun 21 2011, 07:26 AM) *
Using spacers will also decrease cylinder volume. There is no difference between using spacers on the piston head or adding a buffer to the cylinder head...Except that adding a buffer will reduce stress, so the buffer is more beneficial.

The thing with putting a buffer on the cylinder head is that you'd eventually have to replace the foam, whereas you would probably never have to replace washers.

QUOTE (EDI 1st @ Jun 21 2011, 10:42 AM) *
Question about filing down the teeth...
Any suggestion if they are made out of Stainless Steel(?)

A Dremel should work. I've used sanding wheels and cutoff disks on steel without any issues. Just be wary of sparks and the heat generated.
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paparker21
post Jun 21 2011, 06:11 PM
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Good guide star; I'll be doing this on my brand new UMG in just a few days when it arrives.

I'm going to be running around 25-30 RPS and quite honestly I don't want to be back inside it replacing the spacers all that often. I also don't want to increase the pistons mass by that much. I'm thinking of cutting custom spacer out of some polycarbonate. I'll make a hollow cylinder (as little mass as possible but still giving me a good support face for the piston head) and then sand it down to the precise thickness I need for proper AOE. I'm thinking that will give me a light, yet strong, and non-wearing spacer. I should be good to go as long as, or longer than, my gears and/or piston. :)

Although you could probably get away just as easily with some plasticard or even cut-up twist on bottle tops.


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Star_folder
post Jun 21 2011, 07:09 PM
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QUOTE (paparker21 @ Jun 21 2011, 07:11 PM) *
Good guide star; I'll be doing this on my brand new UMG in just a few days when it arrives.

I'm going to be running around 25-30 RPS and quite honestly I don't want to be back inside it replacing the spacers all that often. I also don't want to increase the pistons mass by that much. I'm thinking of cutting custom spacer out of some polycarbonate. I'll make a hollow cylinder (as little mass as possible but still giving me a good support face for the piston head) and then sand it down to the precise thickness I need for proper AOE. I'm thinking that will give me a light, yet strong, and non-wearing spacer. I should be good to go as long as, or longer than, my gears and/or piston. :)

Although you could probably get away just as easily with some plasticard or even cut-up twist on bottle tops.

Most people use nylon spacers for this. Try looking them up.

And while the mouse pad foam wears down fairly quickly in comparison, if you spend the money to get sorbo, it will last much, much longer. I've heard estimates of 100k rounds before 70D sorbo needs to be replaced, you should be opening your gearbox more often then that, just to make sure everything is fine on the inside.


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Cardboard Box
post Jun 21 2011, 09:07 PM
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Nylon, fiber, or even metal washers are an alternative to adding padding to the cylinder head. I prefer to use fiber washers because they're very light but still durable.

If I'm right, Star_folder was talking about doing something like this (the fiber washers are the gray things):


The fiber washers are used as spacers between the piston head and the top of the piston - the weight they add is negligible and they can be found pretty much anywhere. Nylon washers are a good alternative, but they're a bit more expensive.

This post has been edited by Cardboard Box: Jun 21 2011, 09:08 PM
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Star_folder
post Jun 21 2011, 09:16 PM
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QUOTE (Cardboard Box @ Jun 21 2011, 10:07 PM) *
Nylon, fiber, or even metal washers are an alternative to adding padding to the cylinder head. I prefer to use fiber washers because they're very light but still durable.

If I'm right, Star_folder was talking about doing something like this (the fiber washers are the gray things):


The fiber washers are used as spacers between the piston head and the top of the piston - the weight they add is negligible and they can be found pretty much anywhere. Nylon washers are a good alternative, but they're a bit more expensive.

Yes, those are exactly what I was talking about, thanks Cardboard.


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airborne101
post Jun 22 2011, 11:19 AM
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When you add spacers to the piston like Carboard box did, make sure your screw that attaches to the piston head is long enough. There are already issues of screws backing out and causing the piston head to come loose and damage the gun. With the spacers, you have less threads holding it on. You either need to locktite the crud out of the screw or buy a longer one.


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post Jun 22 2011, 01:10 PM
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Ah, the washers will work for my m4- the last owner installed a systema silent ph and ch. I'll have to check the length of the screw, however I recall it was fairly long. Excellent guide star.
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The Blue Dew
post Jul 8 2011, 12:52 AM
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won't doing this lower your fps quite a bit? And do you have to remove a tooth from your sector gear or no? Good guide!
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Cardboard Box
post Jul 8 2011, 01:05 AM
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QUOTE (The Blue Dew @ Jul 7 2011, 10:52 PM) *
won't doing this lower your fps quite a bit? And do you have to remove a tooth from your sector gear or no? Good guide!

Correcting AoE reduces the volume of the piston slightly, so it will lower your FPS, but not drastically. You shouldn't have to remove a tooth from the sector gear - that's only done for short stroking.
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post Jul 8 2011, 10:51 AM
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Great guide, Star. I put a link to this same guide on my home forums.

By the way if you want some pics of what the Sorbo pads would look like, here are some:



I cut those with my laser cutter, but you can do similar work with an exacto knife and a steady hand.


In regards to The Blue Dew's question:
You can shave teeth for two very different reasons. The first is the one mentioned in this thread- to prevent pre-engagement of the gears. This will not affect your FPS (well, possibly VERY minutely as you did change your cylinder volume very slightly). When you shave teeth from the pickup side of the piston, the stroke of the piston stays exactly the same. You don't cause any jumps or anything over the shaved teeth- you just shave them to keep them from being banged up by the pickup tooth.

The second reason to shave teeth is to short stroke. This shaving is done from the *opposite* end of the piston. When you do this, the piston will slip off of the sector gear earlier than normal, and you won't compress the spring as much, leading to lowered FPS at the gain of a faster response from your piston. This is done as a balance against very fast geartrain/motor combos. In some cases, the gears can actually spin around fast enough that the piston is not yet all the way forward, and you can bang the sector gear into the piston midway through its stroke. In the BEST case, you will lose nearly all of your compression since the piston won't go forward all the way, and in the worst case you will shred the teeth on your piston (the middle teeth aren't made for impacts- notice how the pickup tooth is much, much thicker than the rest of the teeth).

Hope that answers your question. And yes, you can do BOTH things to a piston- in fact, if you are to the point of shortstroking your piston, you should have already corrected the AOE with sorbo or spacers, otherwise you could knock off your pickup tooth with an off-center impact.
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Star_folder
post Jul 8 2011, 11:12 AM
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Don't be a pansy.


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QUOTE (Scatterplot @ Jul 8 2011, 11:51 AM) *

I appreciate it, but I wanted to say something about this picture since you posted it and I can reference it.

Putting padding on your piston head like this is a bad idea. See the ports in the piston head, if you put padding on the piston head, you need to cut holes for those ports, else your compression could suffer. This is why I suggest putting the padding on the cylinder head, where you only need to cut one hole for the cylinder head air port.


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Scatterplot
post Jul 8 2011, 11:39 AM
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Yes, thank you for clarifying that. You definitely do not want to cover up the porting on the piston head- I think I have seen a few that didn't have any holes in it, and in those cases adding some padding to the piston head would be fine. I didn't take a picture of the padding on a cylinder head as I didn't have one sitting around, but I did have a piston handy a-wink.gif
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Star_folder
post Jul 8 2011, 11:47 AM
Post #31


Don't be a pansy.


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QUOTE (Scatterplot @ Jul 8 2011, 12:39 PM) *
Yes, thank you for clarifying that. You definitely do not want to cover up the porting on the piston head- I think I have seen a few that didn't have any holes in it, and in those cases adding some padding to the piston head would be fine. I didn't take a picture of the padding on a cylinder head as I didn't have one sitting around, but I did have a piston handy a-wink.gif

lol, I figured as much. It's just that that picture can be misleading.


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buppus
post Jul 8 2011, 11:51 AM
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QUOTE (The Blue Dew @ Jul 7 2011, 11:52 PM) *
won't doing this lower your fps quite a bit?

Normally, this is not a big problem, but in some cases it can be a b*tch. It generally will affect your fps to some degree, because besides removing 1.5-2.5 CC's of volume from your cylinder, it also reduces the length of your piston stroke, which means less acceleration of the piston, and ultimately less power.

So, if you're working with a really short barreled gun, the difference will probably be pretty noticeable - I had a 40fps drop in my MP5K, which I'm already struggling to get decent power out of, so I removed it. Longer barreled setups won't likely see much of a difference, unless it's a really long barrel and you are already on the verge of under-voluming it.

I've also seen this procedure knock 20-50fps off a gun when an uneven buffer is installed on the cylinder head. I assume this is because it doesn't fill the space all the way around the cylinder, and so because the piston head doesn't impact a flat, even surface it messes with the power output.

I recommend this procedure on most V2 gearboxes (with sorbothane), and all high-speed setups. Always do it if you're worried about piston longetivity.


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QUOTE (Zemanova @ Nov 10 2011, 11:18 PM) *
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Stealthmaster14
post Jul 8 2011, 03:08 PM
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QUOTE (buppus @ Jul 8 2011, 12:51 PM) *
Normally, this is not a big problem, but in some cases it can be a b*tch. It generally will affect your fps to some degree, because besides removing 1.5-2.5 CC's of volume from your cylinder, it also reduces the length of your piston stroke, which means less acceleration of the piston, and ultimately less power.

So, if you're working with a really short barreled gun, the difference will probably be pretty noticeable - I had a 40fps drop in my MP5K, which I'm already struggling to get decent power out of, so I removed it. Longer barreled setups won't likely see much of a difference, unless it's a really long barrel and you are already on the verge of under-voluming it.

I've also seen this procedure knock 20-50fps off a gun when an uneven buffer is installed on the cylinder head. I assume this is because it doesn't fill the space all the way around the cylinder, and so because the piston head doesn't impact a flat, even surface it messes with the power output.

I recommend this procedure on most V2 gearboxes (with sorbothane), and all high-speed setups. Always do it if you're worried about piston longetivity.


Couldn't you install a cylinder with greater volume to compensate for the fps loss? For instance, if your gun uses a type 1 cylinder, you install a type 0. Or does that give too much air?

This post has been edited by Stealthmaster14: Jul 8 2011, 03:09 PM


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CharlieLimaEchoE...
post Jul 9 2011, 07:52 PM
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QUOTE (Stealthmaster14 @ Jul 8 2011, 04:08 PM) *
Couldn't you install a cylinder with greater volume to compensate for the fps loss? For instance, if your gun uses a type 1 cylinder, you install a type 0. Or does that give too much air?

I don't think that the FPS drop is enough to require a greater volume cylinder.


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buppus
post Jul 9 2011, 08:58 PM
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Sometimes it is beneficial to add more cylinder volume, but the main reason for power loss is that you are reducing the length of the piston stroke, no matter where the cylinder is ported. That means the piston will spend less time accelerating before hitting the cylinder head; so reduced piston acceleration = reduced power output, just like with short-stroking.

And just like short-stroking, it can be offset by using a more powerful spring, or adding a spacer to your spring guide (as long as there is still enough room for the spring to fully compact inside the piston - may not be possible with bearing spring guides in conjunction with bearing piston heads or piston heads with those large retaining lugs like stock TM PH's). I use 1/2" O.D. brass compression sleeves from Home Depot as spring guide spacers and trim then down to a suitable size.

Like this:


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QUOTE (Zemanova @ Nov 10 2011, 11:18 PM) *
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PapaTurtle
post Jul 11 2011, 04:14 PM
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Instead of using foam or sorbo, I used another rubber pad from a cylinder I had lying around. Will that hold up fine?
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buppus
post Jul 11 2011, 04:43 PM
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It should be fine, as long as the thickness of the whole pad is consistent and it lays flat against both the piston head and the stock pad.


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QUOTE (Zemanova @ Nov 10 2011, 11:18 PM) *
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Scatterplot
post Jul 11 2011, 06:16 PM
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The foam that comes stock in piston heads should hold up well (as it's designed to be in there;))
I've heard that mousepad foam will break down over time and you will need to replace it eventually. Sorbo should last pretty much forever- I've never seen a piece wear out. Not saying that it *can't* happen, but that's kind of why people go for it in the first place (high durability).

I've also heard of people using rubber washers from Home Depot (similar to the kind you would see on a faucet or something) but I've never tried it myself.
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Cardboard Box
post Jul 11 2011, 06:41 PM
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I saw neoprene/rubber washers with the fiber washers at ACE the last time I was there. I was thinking about giving them a try, seeing as rubber might help dampen the impact of the piston head a little bit, but they also might deform and mess up AoE. I'll buy some later on if I ever get the chance and see what happens.
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Star_folder
post Jul 18 2011, 07:58 PM
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Don't be a pansy.


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Used my super leet awesome editing abilities to update the picture of how the sector gear engages the piston before the AoE is adjusted. The previous one was just blurry, and I think the new picture shows the problem a bit better.

I forgot to get new pictures for some of the other blurry photos, but they will be replaced eventually.


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