AustinWolv
04-19-2008, 10:11 AM
Sick of ripping off the back pick-up tooth of pistons in that typical "half-moon" failure? Fairly typical failure on high ROF and high-power guns like support weapons which I encountered often back in the TOP M249 with PGC mechbox days, which was not fun burning through pistons.....and most of the time it was always that same half-moon failure. Ever notice the nipped teeth on pistons from improper clearance from the sector gear rotating around and interfering?
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010644.JPG
It is directly related to how the sector gear engages the piston in typical stock position. Don't ask why they have it that way, I don't know. Perhaps it has to do with how companies just copied each other all these years, so it has carried over and is just the "standard". However, it is easy to tell that it isn't the optimal engagement for gears to make contact and causes unnecessary stress. Some of us have been doing this to guns for quite some time, and typical of mechboxes it is just one of those things to take for granted and not think about, especially since most people don't run support weapons. :doh:
Here's the typical engagement you'll see in a mechbox:
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010649.JPG
See how the sector gear tooth is hitting at an angle? Not good, as you want it to get a better parallel surface-to-surface mesh.
To do that, add washers or some sort of spacers between the pistonhead and piston. You'll need to trial and error it to get the better engagement, which you can see an example of farther below. You may need to use a longer pistonhead screw as a result, depending on the number of washers because pistons and pistonheads are not standard lengths in airsoft. Wheeee. You want the washers to be as close to the diameter of the piston body as you can get them without overlapping obviously so they don't catch on anything as well as wanting to spread out the force on the piston face from tightening the pistonhead screw down. Make sure the screw has enough threads to engage the pistonhead threads and always use loctite so it doesn't come loose.
There are two washers in this case to get the mesh desired:
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010642.JPG
That results in a better mesh as seen below (sorry, I need to take a better straight-on picture.....this mechbox is already assembled so I'll get pictures on the next one I do). You'll also see the shaved 2nd piston tooth so the sector gear can clear it. Hold the piston forward while you rotate the gear to make sure it clears those 2nd and 3rd teeth. Shave them down as needed.
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010639.JPG
Even if you don't use the spacer method, which is entirely fine since guns have run for long times like that (over 30,000 rounds with quality parts) on the typical low spring strengths and average ROFs most use on regular AEGs, be sure to always check the sector gear interference with that 2nd piston tooth. You'll often see that tooth and the 3rd one nipped and worn down on the backside because of this. You should enjoy how seemingly low-regarded pistons will hold up.
For a longer, more complete read on the same subject:
http://forums.airsoftmechanics.com/index.php?topic=956.msg6626#msg6626
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010644.JPG
It is directly related to how the sector gear engages the piston in typical stock position. Don't ask why they have it that way, I don't know. Perhaps it has to do with how companies just copied each other all these years, so it has carried over and is just the "standard". However, it is easy to tell that it isn't the optimal engagement for gears to make contact and causes unnecessary stress. Some of us have been doing this to guns for quite some time, and typical of mechboxes it is just one of those things to take for granted and not think about, especially since most people don't run support weapons. :doh:
Here's the typical engagement you'll see in a mechbox:
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010649.JPG
See how the sector gear tooth is hitting at an angle? Not good, as you want it to get a better parallel surface-to-surface mesh.
To do that, add washers or some sort of spacers between the pistonhead and piston. You'll need to trial and error it to get the better engagement, which you can see an example of farther below. You may need to use a longer pistonhead screw as a result, depending on the number of washers because pistons and pistonheads are not standard lengths in airsoft. Wheeee. You want the washers to be as close to the diameter of the piston body as you can get them without overlapping obviously so they don't catch on anything as well as wanting to spread out the force on the piston face from tightening the pistonhead screw down. Make sure the screw has enough threads to engage the pistonhead threads and always use loctite so it doesn't come loose.
There are two washers in this case to get the mesh desired:
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010642.JPG
That results in a better mesh as seen below (sorry, I need to take a better straight-on picture.....this mechbox is already assembled so I'll get pictures on the next one I do). You'll also see the shaved 2nd piston tooth so the sector gear can clear it. Hold the piston forward while you rotate the gear to make sure it clears those 2nd and 3rd teeth. Shave them down as needed.
http://www.lonestarairsoft.com/forums/photopost/data/500/medium/P1010639.JPG
Even if you don't use the spacer method, which is entirely fine since guns have run for long times like that (over 30,000 rounds with quality parts) on the typical low spring strengths and average ROFs most use on regular AEGs, be sure to always check the sector gear interference with that 2nd piston tooth. You'll often see that tooth and the 3rd one nipped and worn down on the backside because of this. You should enjoy how seemingly low-regarded pistons will hold up.
For a longer, more complete read on the same subject:
http://forums.airsoftmechanics.com/index.php?topic=956.msg6626#msg6626