11 replies to this topic

[maestrojai]

I've had my RIS for about a month now and am having a blast.  The other day I took it apart to check everything out and I have a few questions regarding the piston.  I noticed that the piston moves VERY free in the cylinder to the point that it will just drop through.  There doesnt seem to be a seal there.  I understand that during the course of cycling the oring expands and seals blah blah blah, but what I'm wondering is, would there be any benefit to changing to a ported piston?  If so, what would be recommended?

The gun chrono'd last night at 384-389ish w/.20s at my local field but I'm using .25s.  I'm shooting 11.1v lipos with a mosfet and was just wondering if the piston upgrade (if its considered one) would be worth it.  Also, would there be an increase in fps w/ported (I would assume so) but how much are we talking here.  Gotta stay under 400 w/.20s to play.

The other thing I noticed is that the gun seems to cycle smooth but its somewhat loud.  Personally I think its the sound of the piston making its full stroke because it feels so loose in the gun thats why Im asking these questions.  

My last thread provided me with excellent advice and thats why I figured I'd ask here, Ill take the advice of the KWA guys over my local store/field any day of the week.

[maestrojai]

Now I'm totally confused.  I just removed the rear pin and split the gun, cycled it a few times and the piston will only fully return once about every 3-4 shots.  Im guessing thats because of the variance of air left in the cylinder during the backstroke?  As free as the piston moves in the cylinder per my original post, I would think it would return fully each time...how do I go about getting more consistency?

[niko_gpsy]

maestrojai, on 03 August 2012 - 11:05 AM, said:

Now I'm totally confused.  I just removed the rear pin and split the gun, cycled it a few times and the piston will only fully return once about every 3-4 shots.  Im guessing thats because of the variance of air left in the cylinder during the backstroke?  As free as the piston moves in the cylinder per my original post, I would think it would return fully each time...how do I go about getting more consistency?

A MOSFET with active braking would always set your piston in rest position everytime in semi so there must be a setting on your MOSFET that has been deactivated or is malfunctioning.

[vanevery]

When you are doing the hand compression test, you need to place a finger or thumb over the cylinder nozzle.
If you just drop the piston, it is not going to have resistance.
Also move the piston with some force, a little bit of speed when doing this.
Don't just drop the piston and let it free fall.

It is always a good idea to add a brand new #14 Danco O-ring on your piston head whenever you have the gearbox opened. This will improve your air seal over the stock O-ring.

You do not need a ported piston head if you are remaining with the stock set-up.
A ported piston head will raise your fps but it is hard to say exactly how much.
A lot of things can affect fps.
5-10 fps is a good estimate to go by for a ported piston head, I would say.

I would add one last thing.
Drop in a .02mm shim underneath the Spur Gear and shave off the second tooth of your stock piston,
These are small things you can do that can smooth out the function of your gun.

Edited by vanevery, 03 August 2012 - 02:37 PM.

[maestrojai]

Thanks for the replies guys.

@niko - yeah i know for a fact that the mosfet I have does not have active braking.  Kinda wish i got one that did now that i can actually see how the non braking one performs.

@van - Ill definitely try all of that..I was already planning on doing the tooth on the stock piston as I understand that adjusts the angle of engagement.  I just figured there would be a little more resistance from the piston head when dropping it down through the cylinder.


Thanks again guys, as usual these forums are the best for obtaining info and learning new things.

[vanevery]

maestrojai, on 03 August 2012 - 05:22 PM, said:

@van - Ill definitely try all of that..I was already planning on doing the tooth on the stock piston as I understand that adjusts the angle of engagement.  I just figured there would be a little more resistance from the piston head when dropping it down through the cylinder.

Shaving the second tooth off the piston does not adjust the AOE (Angle of Engagement).
it is necessary to do when AOE is corrected and a good idea to do with any stock AOE.

The second, third, and fourth tooth on a piston can take a beating with any stock AOE at the 1 O'clock position.
What happens is that the sector gear can spin so fast that it engages the piston teeth before the piston has fully returned to its resting/starting position. So it can scrape, snag, or grab the second, third, and fourth tooth.

This not only damages the piston, but the broken piston teeth or piston teeth shavings can get into other parts of your gearbox - namely your gears - and cause more damage.
Shaving off the second tooth can often eliminate these problem with stock AOE.

Keep this in mind.
The second tooth on the KWA piston is encased.
This means you will need to take care and patience as you work the dremel and grinding bit in order to not knick or damage other piston teeth. I use a metal oxide dremel bit with a flat top to it as opposed to common rounded dremel grinding tips.I stay on Medium speed on the dremel for this. It takes longer, but you maintain control without issues of the dremel slipping and damaging other piston teeth.

[maestrojai]

@van - correct.  I apologize for not typing clearly on the AOE...just to make sure I'm on the same page as you, shaving the second gear basically allows clearance for the sector gear when setting the AOE by putting spacers under the piston head...I think thats right lol.  

Forgive me, I'm learning as I go here.  Im still figuring out all of the proper terminology so I can ask questions accurately.   I appreciate the tips on the technique you use for accomplishing this, I'm certainly going to do it.

Thanks again for the help.

[maestrojai]

Ok guys I need more advice (imagine that haha).  Ill try my best to be brief but that may be tough.  

1) took the advice of the posts above and shaved the 2nd tooth off my piston - no problems there.

2) set the AOE but used too small of a washer so the metal insert in the piston by the piston head slid out, broke and basically demolished the piston.  Gears and everything else okay.  No biggy, that was my fault and I know it.

3)put in new piston along with prometheus (sp?) ported piston head along with Danco #14 0-ring.  Here is were the trouble arises.

The gun shoots and sounds fine but now both the motor and battery (11.1v) get really hot after about 100 or so rounds.  The motor gets waaay hotter than the battery.  I took it out, cleaned the brushes and comm etc. put it back in and same problem.

Motor moves freely in the handgrip and the gun cycles great.  My question is this...is the Danco #14 considered an oversized oring compared to the stock one and should the stock KWA motor in my M4 RIS be able to push it with that oring? If it is an oversized oring then perhaps its a combination of the oversized ring and the ported piston head being too much load for the motor?  Please help.  Thanks guys.

Edited by maestrojai, 22 August 2012 - 04:30 PM.

[niko_gpsy]

Your motor shouldn't heat up like you describe after such change. But I'm wondering how well you cleaned your GB and gears of any debris left over from shattered piston. I would also check the bearings to make sure they are not damaged and are rotating freely. After any GB lockup or failure, you should always check the bearings to make sure they are not damaged which can lead to major failure.
Also check along your wiring to make sure it is not being pinched anywhere. This can also lead to over heating.

[maestrojai]

I took the GB completely apart and cleaned it.  I even took a toothbrush to the gears to make sure I got everything out of them as well.  I didnt really check the bearings though.  Ill definitely look at those and the wiring as well.  If I dont find anything I may just put the stock piston with the Danco ring back in it and see what happens.  Thanks again niko, Ill post up what I find if anything.

[aaps59]

You havent touched the mosfet or the wiring since you opened the GB right?

[maestrojai]

@aaps - nope havent touched a thing.  In fact I just now came back in from disassembling/reassembling it again.  No pinched wires, no binding of the gears, nothing.  In fact when I close the gb with just the gears in it, they literally freewheel when I spin them which says the bearings are still okay.  I honestly don't know what else to try.  Guess the next step is to take out that ported piston head and put a stock one back in it.