Full Auto Droop

764 Views 21 Replies 4 Participants Last post by Jimps, 5 mo ago

MrJeff

Discussion Starter · 5 mo ago

Current Build:
SHS 18:1 DSG (8tooth)
G&G 18:1 Bevel & Spur
SHS swiss cheese piston (teeth cut off, 3rd tooth lightly shaved down, AOE corrected)
Lonex POM Piston Head (bearings removed, spring guide has them)
Lonex Full cylinder
Lonex Cylinder Head (one with the pads at the front of the gearbox)
Retro Arms 8mm GB
Matrix Meteorite bushings
Maxx 21.25 nozzle
Tappet plate cut to 11ish mm (Guarder)
Real Deal Tappet Spring
ASG 30k (not the fancy CNC)
Perun Hybrid (in DSG mode, no AB in semi or in full auto, no precock, no ROF control)
Maxx ME Pro Hop-up
6.03 155mm brass Krytac barrel
G&G green bucking
SP150 (Guarder)

Semi is consistent at 355-360, full auto drops to ~330 and then the last shot ends around 360fps yet again. Any thoughts where i'm losing the fps in full or why the last shot returns to normal fps?

1 - 20 of 22 Posts

rm105

· #2 · 5 mo ago

What kind of RPS is it shooting? Shortened the tappet spring? Sounds like a timing issue but could be PME. Try the paper test in auto vs semi (cut out a small square of tissue paper and place it on top of the hop chamber feed tube, see if it gets blown off when shooting - if it does, you've got an air leak). Also try cycling with a weaker or discharged battery and see if the FPS loss in auto goes away (if so indicates issue is speed related; could be PME, could be tappet spring is to weak, etc)

If you've got any pictures of the open gearbox, might help us point you in the right direction

MrJeff

Discussion Starter · #3 · 5 mo ago

~48rps with 11.1v It has real deal tappet springs, would I need to cut them at all? When you say place it on hop feed tube, am I supposed to turn the gun upside down and place it in the magwell practically? If so, it did not move in semi or full. Does this indicate pme? I believe it was quite consistent around 350-355 at 30rps on a 7.4v (will rechrono and post again if it wasn't consistent on 7.4)

mr. potatohead

· #4 · 5 mo ago

Real deal springs are supposed to be stronger than stock springs, so you're probably fine there. And yes, flip the gun upside down for the tissue test.

MrJeff

Discussion Starter · #5 · 5 mo ago

Well it "passed" the tissue test and no air blew it off, so good seal where? Just nozzle to bucking/hop or also nozzle to cylinder head? Just trying to understand what was accomplished passing the tissue test. Where am I losing the fps then?

Jimps

· #6 · 5 mo ago

Run a 7.4v lipo to see if the FPS drop goes away in full auto. That will tell you a lot.

rm105

· #7 · 5 mo ago

Paper test checks for an air leak between the nozzle and bucking - in this instance it tells us you aren't loosing FPS there which tends to rule out a timing issue, weak tappet spring, etc.

~48rps is well within PME territory, do you know the weight of your piston assembly? If it's stable at a lower voltage, try turning on ROF control with your 11.1v and see if that also fixes it. If so, almost certainly experiencing mild PME. Solution is typically to lighten the piston some more. Doesn't take much, half a gram can make a difference. Can also run a spacer on the spring guide to increase the tension slightly (~5mm increments), FPS permitting.

MrJeff

Discussion Starter · #8 · 5 mo ago

Rof control seemed to work great, does this mean that just some piston lightening should do the trick? Is there a good way to further swiss cheese the shs swiss cheese piston. What about expanding the holes on the lonex pom piston head? Could this shave any significant amount of weight or help the o-ring expand faster? IIRC it was about ~17g, will weigh it again tomorrow and post exact weight.

Is 350fps (.20) in correct range for a krytac brass 6.03 155mm barrel with an sp150?

See less See more

Jimps

· #9 · 5 mo ago

I don't think that is the issue. If your piston weighs 17 grams all together, I cant see getting much lighter or it mattering. I have a build at 47RPS with a 20 gram piston and no loss of FPS in auto SP150 at 370FPS.

MrJeff

Discussion Starter · #10 · 5 mo ago

Any thoughts then? Is there a good way to test nozzle tightness, could it be too tight? Is it a possibility enough air can't refill the cylinder in time? Trying to think of everything here I can possibly test.

rm105

· #11 · 5 mo ago

If slowing the cycle down resolves FPS loss in FA and you're not detecting an air leak at the hop chamber, options are limited outside mild PME... Any chance the piston is a little tight in the GB rails or cylinder? Does it mesh OK with the sector gear? Could your AOE require a little more be taken off the 3rd tooth? Can't immediately think of another test or check to rule it out but I agree - PME wouldn't be my first guess with an sp150 and a ~17g piston... If you pull the piston, take a real good look at the pickup on it and hopefully it'll tell us something. What's your battery spec btw?

16:1 DSG SP140 147mm 6.03 ~45rps ~345fps on a lil 3s buffer tube stick

MrJeff

Discussion Starter · #12 · 5 mo ago

Piston slides freely in rails, and I wouldn't say it's tight in the cylinder. May be hitting 3rd tooth but I smacked it a bunch with heavier piston head and m150 so it should mostly be shaved down 😂. Waiting to correct everything before replacing piston body/rack.

Jimps

· #13 · 5 mo ago

When I put a SHS tappet plate in a DSG after 38RPS the FPS would drop in auto. The SHS tappet was shaped wrong causing tappet PME. I swapped to a guarder tappet and the issue went away. You are already using a guarder tappet right? Just double check the tappet spring. I always remove as many coils as I possibly can before compromising the spring/tappet. Put a little lube in the nozzle to be sure it has a smooth action. I was convinced that I had a vacuum issue. I found a clear hose that fit on the end of my nozzle and added some red water in the hose. I then would pull the piston out of the cylinder as fast as I could and measured how much the water moved. I widened the holes in my cylinder head and used a thinner o ring. I tinkered with it until the water did not react to me pulling back the piston. So no vacuum at all. I got around 6-8 FPS gain in auto. My main issue was the tappet plate PME.

MrJeff

Discussion Starter · #14 · 5 mo ago

10

Piston weight 18.7g

I also have already discovered the SHS tappet plate PME haha, hence the guarder I am currently using. Nozzle is lubed, I think it may be a vacuum issue as well, is there a way to know for sure if it's PME or vacuum? What did you use to enlarge the holes on the piston head? (No AB used ever, the slight overspin makes perfect precock haha)

FPS is consistent with ROF control lvl 2, practically no loss in full auto compared to semi at ~42rps. ROF control lvl 1 puts me at nearly 46 rps, but I get ~20fps loss. ROF control OFF gives me 48-49rps but fps drops all the way to ~300.

Anything look off in the gearbox? Seems like theres some wear on the rails where the piston rides, yet it slides freely without cylinder up and down in shut GB. Anyway to fix this? Sand GB? Sand piston rails on piston?

I also believe I have a slight nozzle to cylinder head leak. How should I go about fixing it? I tried to stretch the nozzle o-ring and still seems the same. Should I just switch to Maxx cylinder head? It seems to fit great with the Maxx nozzle. Just opened a friend's GB with Maxx cylinder head/nozzle combo and seemed solid.

Nozzle seems to sit slightly lower in the tappet plate, it's ~1mm "unseated," is this normal?

Also cleaned, re-shimmed and re-greased gears after pics were taken, same result. Used Molykote33 on gears, tappet plate, and piston rails. Used superlube on piston-head o-ring, and nozzle/cylinder head.

See less See more

MrJeff

Discussion Starter · #15 · 5 mo ago

rm105 said:
If slowing the cycle down resolves FPS loss in FA and you're not detecting an air leak at the hop chamber, options are limited outside mild PME... Any chance the piston is a little tight in the GB rails or cylinder? Does it mesh OK with the sector gear? Could your AOE require a little more be taken off the 3rd tooth? Can't immediately think of another test or check to rule it out but I agree - PME wouldn't be my first guess with an sp150 and a ~17g piston... If you pull the piston, take a real good look at the pickup on it and hopefully it'll tell us something. What's your battery spec btw?

16:1 DSG SP140 147mm 6.03 ~45rps ~345fps on a lil 3s buffer tube stick

Battery spec 11.1v 3000mah 50C Zeee

Jimps

· #16 · 5 mo ago

The ASG Ultimate cylinder head is OP. The OD of the stainless nozzle rail insert is greater than most cylinder heads. It allows for a tight fit on the nozzle. Less worry about midcap syndrome. Don't use the Maxx cylinder head in the RA gearbox. It will knock the guide pins off. You don't even really need an o ring nozzle. Air wont leak there unless it is REALLY loose. I would remove 2-3 coils from the tappet spring. You have plenty of coils to remove some. Yes is is normal for the nozzle to not seat all the way in the tappet. Is it good, no. Not much you can do about it unless you have an injection molding factory and knowledge of CAD, a CNC machine would work as well. LOL. Some tappet plates are different and the nozzle will seat further down the tappet. I have designed a 3 piece tappet in CAD that fixes that issue. I need to cut it on my friends CNC mill for testing. I used a hand drill that came with a micro drill bit set to widen the holes in my piston head. Probably 0.3-0.5mm bigger.

See less See more

Jimps

· #17 · 5 mo ago

This is the ASG Cylinder Head. Sold at Brill. I also like the Tienly Cylinder Heads.

Rectangle Gas Electric blue Magenta Metal

See less See more

Jimps

· #18 · 5 mo ago

Not sure what piston you used. I had a bunch of the SHS 15 tooth pistons have issues. The rack is a little off alignment. Not sure if it was a bad run or if all of them were bad. I use Rocket 14 tooth pistons and have not had issues. Look closely at the gap between the teeth and rack when the gear spins. I had like 15 piston racks I had to trash, this was one of them.

Reactions: 1

MrJeff

Discussion Starter · #19 · 5 mo ago

Jimps said:
The ASG Ultimate cylinder head is OP.

OP?

Jimps said:
This is the ASG Cylinder Head. Sold at Brill. I also like the Tienly Cylinder Heads.

I have this ASG one

Automotive tire Automotive lighting Rim Auto part Font

Should I order the other one or is this one ok?

Jimps said:
Not sure what piston you used.

I used the SHS swiss cheese 15T, will check for the teeth not meshing properly tomorrow, but I feel like I would have noticed that, especially considered how long i stared at the damn thing today going back and forth.

Jimps said:
I found a clear hose that fit on the end of my nozzle and added some red water in the hose. I then would pull the piston out of the cylinder as fast as I could and measured how much the water moved. I widened the holes in my cylinder head and used a thinner o ring. I tinkered with it until the water did not react to me pulling back the piston. So no vacuum at all. I got around 6-8 FPS gain in auto. My main issue was the tappet plate PME.

I think this could potentially be adding to my problem, but do you think it'd be a big enough vacuum to lose 50fps on full? Considered with ROF control on lvl 2, at 42rps, it is lossless on full.

Anything else you can think to check for? I know damn well I'm going to be mad when I find out it's something so simple...

See less See more

Jimps

· #20 · 5 mo ago

I like the ASG with the stainless steel insert. It is slightly oversized and nozzles fit snug. That prevents the bbs pushing the nozzle up because the is very little play between the cylinder head and nozzle. You probably don't need to change the one you got really. If you do I like the one I pictured. They are $13 on Brill Armory. I would still shorten the tappet spring coil. At least 2-3 coils. OP= On Point. I still don't now if I'm a believer in the vacuum thing. I do it on all my builds because it does not hurt anything to do it. I did bump up a few FPS after but I bumped up FPS at 38RPS and 48RPS. Tappet timing was my main issue. Yea best to check the piston. One way is to spin the gears by hand, without the spring in obviously, with the gearbox together, and see if you feel a slight snag. I use a metal pick to spin the bevel gear, see if you feel it snag right after the pickup tooth. Probably not related to FPS issue but could be an issue nonetheless. You can check it like in the video as well.

See less See more

1 - 20 of 22 Posts