[mr. potatohead]

Haven't been able to get into my gb and won't be able to til next week but I keep trying to visualize what the problem could be...if my tappet plate is long enough to fully pull back the nozzle, but still "pretty short," could that cause problems, specifically air leaks? Other thing could be my nozzle, which is stock and wiggles mildly but I guess I won't know for sure til I open the gb up...this problem has just been eating me up these days (past few months actually), but I know I'll feel great once it's resolved.

 

[mr. potatohead]

Would appreciate some feedback on my gb...might be something I'm not seeing.

 

[rm105]

Tappet fin looks a little sketchy but if its feeding that's probably not it. How's the spring on your tappet look? I forget if you shortened it already- if not, might take a coil or two off and see if that helps? When your nozzle is a bit sloppy having a stronger spring can help it seal more consistently

 

[mr. potatohead]

It feeds fine and my tappet spring is shortened...I cut my tappet pretty short bc I wanted to make sure my nozzle was seated before my piston assembly slams forward.

 

[mr. potatohead]

Switched my stock nozzle for one with an o ring...did this to see if it would help the nozzle stabilize...on semi it chronos ~320 and then ~310 every other shot. I have no idea how to go about fixing that. Full auto is still around ~200 fps. Only thing I haven't considered is my hopup bucking, maybe it doesn't like to seal well?

 

[Guges Mk3]

Leave your upper off. Watch piston position after each shot. Does it stop in the same place each time?

 

[mr. potatohead]

Leave your upper off. Watch piston position after each shot. Does it stop in the same place each time?

Hmmm I've actually done this before and no, it doesn't...it sometimes does, but other times it will be in a slightly different position. Does that signify anything beside mild PME or overspin?

 

[Guges Mk3]

For the piston.

It could stop in a non-zero home position. This is dependent on what part of the cycle it stopped on. It may be a "retarded" release, i.e. the piston was "caught" on the forward stroke and the piston drops say 1/5 of the way forward. Then when you pull semi again it drops the rest of the way at 4/5th stroke and your air pressure is lower than a full stroke...thus your every other high, low, high, low, readings.

My E&C was doing that 3 weeks ago due to over spin...every other shot was a low fps shot in SA. I switched to a LIFEPO4 battery and that remedied the situation until I had to use the 3S LIPO again. Then when the LIPO drained a fair bit my high, low, high, low fps went away.

 

[mr. potatohead]

When hooked up to a 14.8 v lipo, my semi readings dropped to ~250...also there was massive overspin...this supports your diagnosis, right?

 

[Guges Mk3]

Yes, it is leaning that way. Up the spring rate to the next level and it may go away.

 

[mr. potatohead]

Interesting. At least I kinda have an idea of what's causing these issues now. I don't think this explains the massive fps drop in full auto, so I guess there's something else in addition to the overspin that's a problem.

 

[rm105]

Check for wear or rubbing on the piston rack, can help point us in the right direction.

If the piston is being caught mid cycle or has PME every other shot during semi the issue will be more pronounced in FA. A stronger spring as Guges suggests will definitely get the piston home quicker but it will also increase FPS an arbitrary amount. Alternative options are to add some spacers to the spring guide to increase tension while maintaining some control over FPS, using a even lighter piston assembly, or running a slower motor. Forget which motor your using but been seeing a lot of issues lately due modern motors being marketed as 'faster better'.

 

[mr. potatohead]

Will do. Currently I'm using a Guarder sp140 with an ASG 30k boost...I've experimented with stronger springs and spacers and still had massive fps loss in FA.

 

[mr. potatohead]

Well @rm105 to answer your question, the last piston tooth is just fine, so I doubt PME is at work here. Furthermore, my entire piston assembly is 17 grams.

My accuracy is...tolerable. One thing I can't figure out is my low rps...I'm using an 18:1 DSG gear set with a 30k motor and an sp140 and getting ~35-40 rps on a half charged 11.1v, and my 12:1 SSG build before this was getting ~35-38 rps on a crappier 11.1v lipo...I'm pretty sure my build should be faster, but can't figure out why. Would appreciate any ideas thrown out there.

 

[rm105]

Something in there is leaching, an 18:1 DSG is 9:1 as compared to 12s... I'll read through the thread and speculate once I get back, out camping for a couple days.

Did you turn ROF control on earlier? 30k so probably 16tpa, wonder if the motor isn't hitting peak rpm before the cycle completes due to load etc... Noticed the battery draining quicker than usual?

 

[mr. potatohead]

ROF control is off, and I'll have to do a test with the battery to confirm if a heavier spring is causing the motor to flounder.

 

[mr. potatohead]

Well if anyone's been following the thread, I'll give ya a quick update. Going to be doing some experiments with a ASG 30k motor vs. a ZCI high torque with varying spring strengths (ordered too weak of a spring so I'm gonna have to wait a bit on this experiment).
I have diagnosed my drastic FPS loss in FA as tappet PME...It appears I still do not quite understand how to trim a tappet properly; I've reviewed the advice I've gotten and will try again with another SHS tappet (I have an SHS DSG gear). I have a couple questions: I know that cutting a tappet too short (I did in my case) is not great (except in a TSG), but why? How does that still create air leaks? Since my nozzle is already being yoinked back before my piston returns fully, would I be able to fix that with a tappet plate that has a longer dwell time (was it Lonex or KA?).
On the topic of ROF, I ordered some 16:1 gears and 8mm bearings...I suspect metal dust got into my bearings during a dremel session (I was too stupid to knock them out or cover them) and may by slowing my build down. Anyway, that's all that's new.

 

[rm105]

Cutting the fin to short means it will come off the pin earlier than is ideal - in theory at least, should only cause feed issues. The shape of the fin might be more at fault here if you're suspecting the tappet - if it's release is to gradual it'll slow the nozzle down and possibly prevent it from sealing very well during FA. I like to round the front corners on mine a tiny bit to reduce 'over feeding' (when the spring snaps forward so quick it pushes the BB into / past the bucking mound) but it's a subtle difference. Maybe try just sanding the bottom of the fin flat this time, not touching the front or rounding the corners at all, and seeing if that improves your FA FPS?

Note how abrupt the transition is from the front of the red fin vs how gradual it is on yours.

From the back forward: SHS, KA, Lonex. The slightly different fin positon + shape effects pickup timing which can be useful to fine tune your build - IE, if your pickup a bit to early, try a KA or Lonex.

With a TSG the space between pins on the sector gear is so tight you have to make sure the tappet is able to fully return between them - in this pic the fin just came off the left pin but as you can see the upper-right pin in is almost picking it back up again; if the fin was a hair longer it would bounce from one pin to the next without ever allowing the nozzle to seal.

 

[mr. potatohead]

What's interesting is that I haven't had any feeding issues (~40 rps) except towards the end of a magazine when spring tension is low.

 

[mr. potatohead]

Well, well, well I popped the mechbox open and lo and behold, the spur gear is missing teeth . I will try attaching a few pics for your guys' amusement tmw. I forgot where these gears came from except that they were stock 18:1 and from either a dytac, lancer, or cybergun (yes I'm ashamed of myself for even thinking this would be a good idea). Glad nothing bad happened. I also found my neoprene flapping around completely free in my cylinder so that's cool . Bearings (new ones are 5KU 8mm) are replaced but they stick out a lot compared to the previous ones, causing friction with the selector plate.

EDIT: SCREW this no standards industry . Good grief I spent about 20mins shimming my gears to the new bearings. Turns out I can't even get my gearbox back into the lower because the darn bearings can't get past the fire selector gears! WOW. I don't know what to do from here, maybe I'll just go order a set of 8mm low profile bushings as it's harder to find low profile bushings. I'm sorry wallet