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Discussion Starter · #1 · (Edited)
Hello all. I need help from the collective here.
I've been having some issues with my UTR45 build.
11.1v quality batteries
Perun Hybrid V2
Lonex blue piston and POM head
Lonex cylinder head and MAXX cylinder
MAXX 21.25mm nozzle (same length as stock nozzle)
13:1 gears, short stroked 4 teeth
Krytac hop up with ML macaron 60" packing. ( 1st 2 outings krytac orange)
Lambda 6.03 barrel
22k 22tpa ASG Infinity motor.

It's first day on the field everything worked fine. The thing shot lasers. If I recall correctly, I may have been running lesser quality batteries.

The second time I took it out, I would get some random shots that would drop too early.
I suspected compression/seal issues, so I replaced the bucking from Krytac orange to ML macaron 60*

Took it out for it's first day back on the field yesterday and was still having the exact same issues.

This time I tried to pay closer attention to what was going on.
Some shots would drop way too early and sounded weak, like the compression was off.
It was random. During spam and slow fire. No rhyme or reason.

Listening back on the video, I think it could possibly be PME, as some, but not all of the weaker shots I would hear a slight clicking sound.

When I built it, I only removed a few teeth from the piston. Should I remove the remaining unneeded teeth?
What would you do?
Possibly remove the extra teeth from the rack and double check airseal, stretch of the oring a little?

ETA: This is a pic from when I built the gun.



Here is a short video where you could hear it the most. SOme of the shots were hitting so low, they were hitting the barrier I was shooting over.

If I left anything out that is pertinant to the troubleshoot, let me know.

 

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Discussion Starter · #3 ·
Not seeing the typical signs of PME (chewed up pickup/rack). Did you see the same issue with a lower powered battery (7.4v instead of 11.1v)? What spring are you using?
Sorry, that picture is from when I built it. I haven't taken it apart yet. Was going to try to rip into it tomorrow.
Previous batteries were also 11.1v, just lower quality ones.
Spring is an M105 asg I believe.
 

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Discussion Starter · #6 ·
Okay. Sounds like a plan.

Since I pretty much exclusively shoot semi-auto, would a potential fix be removing one more tooth from the sector pick up side, and using an m115 or m120 spring?
 

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Discussion Starter · #10 ·
M115 or M120 would almost certainly eliminate PME being a possibility. Ona side note, don't maple leaf macaron packings require a bit of modification to work properly?
Yeah, they definitely require a little bit of trimming. I found a pretty good method to take care of that. It drops about 5 or 10 FPS but it feeds 100%. What I do is use a one and a half inch Dremel cutting wheel, and just barely kiss the lips to the face of it. It removes material very evenly and smoothly.
 

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Discussion Starter · #11 ·
Potentially, although 5t SS could start messing with your timing - may want to take one off the release side instead. What's the current FPS (before it started acting up)?

Personally, I'd start by using ROF control and/or a 7.4v to ~confirm if it's PME. If it looks like it is, you may be able to get away with just lightening your piston assembly some more - every g you remove gives you more headroom and you might be right on the edge if it cycled ok previously. Get that piston assembly under 20g one way or another lol. If that doesn't do it then I'd try adding a spacer to the spring guide to give it a bit more oomph if you can gain a few fps while remaining legal - if not, stepping the spring and taking another tooth off may be needed. Or be lazy and just use ROF control to keep everything in one piece - definitely done than a few times.
Sorry, forgot to mention. FPS was 350 with the Krytac orange. After trimming the macaron down for proper feeding, it was around 342, which was ok with me.
I try to keep everything around 350fps. Although, I could go up to 400, but MED changes from 10ft to 20ft, but I could probably live with that.

I will try the suggestions with the battery etc before ripping into it and see if anything changes.

I also should have mentioned. The sector came stock with a delayer chip on it. Not sure how much that would play into helping or hurting if I did end up needing to remove 1 more tooth from the sector.

Since i want to take everything apart to see how the insides are holding up, I think I will definitely lighten the piston, and remove any teeth from it that aren't needed. Pretty sure I still need to take off 1 tooth. That should lighten it up a bit. I'll finish the swiss cheesing I started, as shown in the picture above.
I don't remember if I left the bearing in for the piston head. If I did, I may remove that while I'm in there.
 

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Discussion Starter · #13 ·
For sure.
Last time I was at the hardware store, I went prepared with a list of measurements to hunt to nylon spaces for correcting AOE and other various parts. I found some in the exact sizes I would need to replacing the piston bearings. I'll see how those hold up. I believe they are the off white nylon type spacers. They seem pretty stiff and durable.
 

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Discussion Starter · #18 ·
Take off your upper receiver and fire a few rounds in semi. Make sure that the nozzle ends up in about the right place, or it could potentially be causing feeding issues. Active braking can help with this.

I've seen instances where the nozzle stuck, or even the tappet timing was off where the nozzle would return and extend in the wrong places. The nozzle could even be pushing BBs too far past your hop rubber.

Do you own a chrono? Some chrono results would be really helpful.

Look up the silicone cylinder head buffer mod. I've found it to be extremely easy and useful. You can add more material than you need and correct AOE exactly with a razor blade, it's a soft buffer, piston sound is a lot better, silicone immediately returns to its original shape, so your FPS will be more consistent. I've never had any damage (yet) either.
I will get some chrono results before doing anything. My chrono seems spot on with my fields chrono in regards to FPS. It does suck at measuring RPS though.

Sounds good. I'll check in on the nozzle positions before ripping the gearbox open.
I haven't had a feeding issues, at least not to where a BB didn't fire. But I get what you're saying about the nozzle potentially pushing the BB past the hop rubber. That could definitely cause FPS drops I would assume.

I'm not so concerned with the gun being loud, as much as I can hear an occasional clicking sound when the shot seems to have low FPS.
That's why I was thinking mild PME, but being so new, I'm not 100% sure what to be looking/listening for.

My though process was if there was any mild contact with the sector gear while the piston was returning towards the cylinder head, it would produce a weaker shot.
I mean, I think the piston release tooth is ever so slightly contacting the sector pickup tooth on it's way back forward.
That's the only thing I could think that is making that clicking sound when there is a weak shot.

It's really hard to hear in the video. It is very faint, but you can hear some shots sound slightly weaker at the same time there is the clicking noise.

Spots in the video where you can here it
23-24 second mark.
29-30 second mark.
34 seconds
and at the 49 second mark I shoot a slow 3 round burst.
The first shot sounded and shot normal. The 2nd and 3rd shots had the clicking noise and had weak FPS.
 

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Discussion Starter · #22 ·
Ok. I got some chrono data.
Started with a 7.4v 1500mah 60c rc brick.
Velocities were very consistent and all shots sounded the same.
Product Font Material property Electric blue Handwriting


Full auto burst
Font Material property Tints and shades Electric blue Circle



Then moved on to the pack I use the most.
11.1v Turnigy nano tech 1200mah 25-50c crane pack.

Out of 36 shots, I had 2 that were in the 250 range. Those 2 shots sounded weak and kind of springy.
Font Material property Electric blue Handwriting Number



Full auto burst had a few low shots
Light Font Material property Circle Electric blue



Whatcha guys think? I'm hoping it's pme, as I think that'll be easy for me to fix.
 

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Discussion Starter · #24 ·
Not seeing drops on 7.4v narrows it down, PME is a strong contender but usually it's more consistent in auto than you're seeing... Might be because its marginal? Piston rack will tell the tale.

How's your nozzle look/feel btw? Got good spring tension, feel smooth, no/little wobble, centering OK, etc?
I haven't had a chance to crack into it yet. Most likely not until tomorrow evening. I will check and report back for sure.
 

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Discussion Starter · #25 ·
I still haven't had time to crack into the UTR45 yet. Turnout on my Black Friday sale was a lot bigger than I expected. I'll be sewing slings when I'm not at my 9-5 for the next 8-9 weeks straight!

If I can squeeze in an extra hour or 2, I hoping to be able to do it sooner, but it is looking grim.
But I am still thinking it is some mild PME.

I'm also going to take a close look at the piston rails while I'm in there.
When I built this up, the piston was tight in the rails.
It it so intermittent, that I suspect that is not the issue though.

I was also thinking to take another close look at the tappet plate guides in the gearbox.
That was also a little tight when I put it together, but I very lightly sanded/polished the tappet plate and cleared away flashing from the GB when I built it as well.

I'll report back once I've gotten into it.
 
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