Can someone give me the lowdown on piston AOE?

[crunkathon2k]

I have recently been reading up on Piston AOEs, and I was wondering if someone could give me a guide on how to do it.

 

I'm very sorry if this has been covered before, but the search doesn't seem to work because "AOE" is too short.

 

Based on what I already know, do you have to:

1. put a washer between the piston and piston head

2. Remove the second to last tooth on the piston (using the metal tooth as the reference point for the first tooth)

 

Is this process all-encompassing, or do you have to add different amounts of washers for different setups? Also, how will this affect my setup with a systema silent kit?

[RSM]

This is how I go about figuring out how much my AoE needs adjusting:

 

1) Place 'compression assembly' (cylinder, cylinder head and piston) into gearbox as well as sector gear

2) Using a pencil/sharpie mark a line on the piston by using the back edge of the cylinder

3) Rotate the sector gear until the angle of engagement is so that the first tooth to meet the piston is completely flat against the piston pick up tooth.

 

4) Mark another line on the piston using the back edge of the cylinder.

 

5) Measure the distance between the two points and this will tell you the amount of adjustment required

 

You will need to remove piston teeth 2 and 3 (after the pick up) to prevent premature engagement of these teeth once the AoE is corrected.

 

To sort the AoE you can either fit spacers between the piston and piston head (I made small discs out of airsoft gear packaging) or you can use epoxy and rubber washers to 'stack' the cylinder head. The latter method is more useful if you need to acheive more than 2mm of adjustment as that is all you can get away with in the washer method if you want the locating lug on the piston head to still reach the piston.

 

You might need a slightly longer screw in your set up and the convex nature of your piston head precludes you from the washer method, unless you are running a high speed set up (22rps+) then AoE correction isn't entirely necessary but post the specs of your gun and more specific info can be provided.

[crunkathon2k]

Oh heck, I'm only running a m100 with a 9.4V Nimh battery. It's not even close to a high speed setup, I just thought that AOE was necessary for proper gearbox optimization.

 

Thank you for the helpful and informative post. I'm sure others will find this useful.

[infected]

RSM, good explanation of how to measure that out. I might just need to "borrow" that for an upcoming article on my website, if you don't mind .

 

AOE correction is worth it on most AEG's as it reduces the wear and tear on the first few teeth to come in contact on both the sector and piston. It's not just a ROF thing, but in a high fps gun with a li-poly battery, it will save your piston from losing it's first tooth.

 

I had my m14 running at near 500fps, and then put a li-poly in it. The speed with which the sector came around, snapped the back end off the piston like it was made of glass. I then installed a new piston, and corrected the AOE, and it's yet to happen and it's been running for about 700 rounds. Keep in mind, it's shooting near 500 fps, semi-only, and with an 11.1v li-poly and a mosfet. Trigger response like a dream.

[RSM]

Sure you can post the method I use but can you please credit Docv400 (another member on here) as guiding me toward taking measurements that way to be absolutely sure of the right amount of spacing required - I found that I needed 5mm of adjustment which required a custom cylinder head stacker to be machined.

 

I should have clarified that AoE correction is not totally necessary in stock level guns but as you say, high 'piston impact' set ups (be it high fps or high rps) will need adjusting. I'm in the process of upgrading a mildly high speed (21rps) CA36K thats been running at 320fps for about 8 months now and inspecting the piston there is only a little bit of wear on the pick up, similarly there is an ICS M4 thats 3 years old still on its stock piston/piston head and spring that's been ran at around the 18rps mark at 340fps and there is very minor wear on the pick up tooth.

 

On the flip side though, before I corrected the AoE in my M4 that runs anywhere between 27-30rps depending on the battery condition I could expect to blow through a piston within 2 skirmishes, now with the AoE sorted the piston I dropped in still looks the same as it was when it was brand new about 20,000 rounds later.

[crunkathon2k]

Wow, that's a huge difference.

 

What kind of washers are necessary? Do they have to be metal to ensure piston stability and minimize wobble? Also, I never really understood why you need to remove the tooth next to the pickup tooth- can somebody explain that for me?

[RSM]

Like I said I had some packaging from a set of prometheus gears (the sort of plasticky stuff that a lot of electonics goods come in and is impossible to open without a pair of scissors or knife) I just cut some circular discs from the packaging, drilled a holed big enough to get the piston head lug through and started stacking that way. If you want to stack the cylinder head using epoxy then 20-23mm rubber washers 2mm in thickness could be one way to start.

 

In normal set ups, removing the number 2 (After pick up) tooth helps prevent premature engagement, that is the sector gear coming round and picking up the number 2 tooth instead of the actual pick up tooth, when this happens the piston still gets drawn all the way back but there is still a sector gear tooth to go through the gears rotational cycle, the piston being the weaker of the two (usually) fails as the gears shove themselves through the material.

 

When correcting AoE for high impact set ups, you have to remove teeth 2 and 3 to allow clear passage of the sector gear as these teeth are often where the pick up would be in a normal piston set up.

 

AoE correction has a slight drawback depending on how you go about it, for example in my M4 when I dropped in a 5mm spacer it reduced the overall volume of air in the cylinder - this resulted in a 30fps loss in muzzle velocity.

 

The way of correcting this was fitting a cylinder designed for 455mm barrels (as opposed to 363mm, remember there is no risk of suck back or premature release of the BB because the spacer reduces the overall volume in the cylinder) and a bearing spring guide to preload the spring a little bit as well as improving its life span - result was 350fps at 30rps.