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What did I do wrong? Bucking suggestions! Prometheus Tightbore & M120 spring


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#61 EzDeezer

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Posted 16 July 2013 - 10:27 PM

It looks like that padding did come off the back of the cylinder head, but I'm not completely sure, I would wait for someone with more experience to confirm.

Edited by EzDeezer, 16 July 2013 - 10:27 PM.


#62 rawfuls

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Posted 16 July 2013 - 11:29 PM

Ill be pulling jr apart one last time before I give it to the local shop.

Should I put the pad back in?

I believe it'd be easier for them to chrono the 120 spring and see its obvious bad readout than to explain.

#63 nbv386

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Posted 17 July 2013 - 07:41 AM

I think he was talking about the sorbo on the pistion head not the cylinder head. You want sorbo on the cylinder head but not neccicarally on the pistion head. Also the pistion head is connected to the pistion( the part with the teeth) and moves inside the cylinder.

#64 gcw360

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Posted 17 July 2013 - 02:41 PM

View Postrawfuls, on 16 July 2013 - 09:37 PM, said:

I just pulled the sorbo pad off- and will be trying it shortly.
Here are the pictures of the cylinder and cylinder nozzle/head.

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Looks like there is an o-ring missing from the cylinder head (See the groove in the cylinder head? it should have an o-ring in it)....that would be a significant issue causing a drop in compression.  I would start there.  It my not be the only issue but my guess it's the major one.

#65 rawfuls

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Posted 17 July 2013 - 04:05 PM

View Postgcw360, on 17 July 2013 - 02:41 PM, said:

Looks like there is an o-ring missing from the cylinder head (See the groove in the cylinder head? it should have an o-ring in it)....that would be a significant issue causing a drop in compression.  I would start there.  It my not be the only issue but my guess it's the major one.

Whoops, there actually was a oring in there, but I removed it for cleaning.
I decided since I'll be out of town until next week, and as a computer tech, it's annoying when our clients mess up their computers 'trying to fix it', that I'd just drop it off for the pros.

He took the M4 into the back, chrono'd, came back with eyes wide open and said it chrono'd 250.
Defintiely thinks it's a compression issue: asked for a rough ballpark quote and he quoted me $45-65 for everything.
At this point. just want it over; and I'm curious as to what exactly is the issue.
My bet, is that it needs a new cylinder head/piston head.

$35 for labor charge (flat rate) + parts, that doesn't seem too bad...

I'll keep you guys updated; he said he'd call and make sure I approve the work before it begins.

Hopefully it ends up near the 400fps mark.

#66 gcw360

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Posted 17 July 2013 - 05:35 PM

View Postrawfuls, on 17 July 2013 - 04:05 PM, said:

Whoops, there actually was a oring in there, but I removed it for cleaning.
I decided since I'll be out of town until next week, and as a computer tech, it's annoying when our clients mess up their computers 'trying to fix it', that I'd just drop it off for the pros.

He took the M4 into the back, chrono'd, came back with eyes wide open and said it chrono'd 250.
Defintiely thinks it's a compression issue: asked for a rough ballpark quote and he quoted me $45-65 for everything.
At this point. just want it over; and I'm curious as to what exactly is the issue.
My bet, is that it needs a new cylinder head/piston head.

$35 for labor charge (flat rate) + parts, that doesn't seem too bad...

I'll keep you guys updated; he said he'd call and make sure I approve the work before it begins.

Hopefully it ends up near the 400fps mark.
We'll be interested too.  Thank you for keeping us posted.

#67 rawfuls

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Posted 20 July 2013 - 01:21 PM

Got the call from the local shop (True Edge in Winnetka).
They said they found the head cylinder had "exploded" which is actually possible because I remember seeing the back plate fairly loose. However, exploded is probably exaggerated.

Regardless, they said they replaced the cylinder head with a ?GPU? (That's what I heard over the phone, probably a different brand) head for 24.99 parts fee, and the 35.00 labor.

I do hope it's an aluminum or a quality brand as I see a plethora of cheaper heads online.

I asked for the FPS rating, to which they said it shot 310 with the "CQR" cylinder, with the 120 spring.

I found this to a tadbit suspect.
Does a stock cylinder with a prommy 120 spring REALLY shoot 310?
They said next step would to be removing the stock cylinder and replacing with a Type 1 or 0.5.

At this point I'm not sure if I'm happy.

What do you guys think?

I did tell them to call me with quote before proceeding, so technically I could fight them for the new head and replace it myself, as long as I pay the labor fee; however not too sure if I want to play that card..

Pick up is tomorrow 12-4, otherwise until Wednesday.

#68 vanevery

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Posted 20 July 2013 - 01:31 PM

M120 spring and 310fps is correct for that Cylinder. A simple change in Cylinder will get you to 400 fps. As for the Cylinder Head, It will be hit or miss due to the Cylinder Nozzle being a sensitive area to performance in KWA guns.

#69 rawfuls

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Posted 20 July 2013 - 01:58 PM

I thought the stock spring will shoot up to 350fps?
What's the recommended cylinder for just a little over 350fps?

#70 rawfuls

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Posted 21 July 2013 - 07:04 PM

Picked it up this morning, pleased- for the most part.
Now that I think about it, I DO remember the plate that held the air nozzle tight against the head cylinder WAS wiggly.
Dumb me, as soon as I dropped it off, left, and a few days before they called me, it hit me that, it was NOT supposed to be moving!

Ah well, at least now I know it's fixed with a 30 day warranty.
However, the safety isn't working- and after a specific poundage, the trigger is flipping right into semi (trigger will stop itself, until I put more pressure, and then it gives.)

I'll attach the pictures, they said they opened it up and the cylinder head plastic pieces just fell right out (not how I remember it... I feel like they crushed them..hmm) so they threw in the JBU Cylinder Head (JA-11) Version 2.
Marked at $24.99 + $35 labor, came out to $62- and they had to throw on the orange tip before work proceeded.

Did the poor man's chrono, going through both sides of the can easily.
Feels MUCH better and stronger- happy, but I don't think it's JUST shooting 310.. :clap:

I'll fielding it this coming weekend, with a chrono, then put a tightbore in, chrono- and if I feel as though I should get a Type 1 Cylinder, what are the recommendations?

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Edited by rawfuls, 21 July 2013 - 07:27 PM.


#71 EzDeezer

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Posted 21 July 2013 - 07:19 PM

I like Guarder cylinders, I believe they make a type 1, or just put in a regular KWA type .5 if you can get one.  The new cylinder will also help out your range if you put in a longer barrel, but don't go past about 425mm with the type .5, for ~450mm and above, a type 0 cylinder is the best.

#72 rawfuls

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Posted 21 July 2013 - 07:33 PM

View PostEzDeezer, on 21 July 2013 - 07:19 PM, said:

I like Guarder cylinders, I believe they make a type 1, or just put in a regular KWA type .5 if you can get one.  The new cylinder will also help out your range if you put in a longer barrel, but don't go past about 425mm with the type .5, for ~450mm and above, a type 0 cylinder is the best.

I've heard that with a 363 or even stock CQB barrel, having a type 0.5 or 0 cylinder will decrease your performance as the air being compressed is so great that it will exit the air nozzle without the piston being able to finish it's compression?
If anything, it will be a stock CQB barrel or 363mm, the guy at the shop said Type 1 would be best?

I also don't want to be carrying around a gun shooting over 400+, as that's the field limit for the outdoor field.

#73 EzDeezer

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Posted 23 July 2013 - 12:58 PM

I meant to say for longer than 363mm the type .5 and for above 450 the type 0, a type 1 should be fine for 363mm.  There is a table somewhere that says the perfect barrel length to cylinder matches if you can find it.  I wasn't aware that KWAs could really take aftermarket cylinder heads, but I guess some do work, the JBU one is in your KWA right now I assume?

#74 rawfuls

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Posted 23 July 2013 - 04:20 PM

View PostEzDeezer, on 23 July 2013 - 12:58 PM, said:

I meant to say for longer than 363mm the type .5 and for above 450 the type 0, a type 1 should be fine for 363mm.  There is a table somewhere that says the perfect barrel length to cylinder matches if you can find it.  I wasn't aware that KWAs could really take aftermarket cylinder heads, but I guess some do work, the JBU one is in your KWA right now I assume?

Yup, JBU head in the stock cylinder.
I went plinking with about a thousand rounds in the backyard for awhile yesterday to break everything in- feels like it shoots a lot harder than 310.

I'm going to go indoor sometime this or next week, and an outdoor field an upcoming weekend and get the chronos from the two field, then throw in a tightbore and see how it performs.

#75 vanevery

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Posted 23 July 2013 - 05:36 PM

Glad the gun is working and that you are happy with the results.




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