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Put air in FD PCP for first time. Shoots HARD! Then leaked, then valve locked. LOL.

April 26 2017 at 9:28 PM

John in FL.  (Login gratewhitehuntr)
AR&P

Shooting co2 and 8gr pellets i had it tuned to juuuuuuust kill squirrels. Maybe 650?
On air it was splattering the 10.5gr on a brick!

Second fill it'd only fire right after cocking, waiting even a couple seconds would result in a fart, then the next few shots got progressively hotter.

Third fill it'd only fart, then nothing.
Pump gauge reads about 1600, think it was around 1400 when it locked (or whatever) and I added a little trying to decide if it was accurate.

I have several hammers, from a few grams up to 20LBS.
Which fits this gun?


Is there something else going on here? I think the hammer is functioning normally, but the valve just isn't opening.
Going to degass this weekend, seems like it came with some orings.
Maybe the bstaley mod while I'm in there....



    
This message has been edited by gratewhitehuntr on Apr 26, 2017 9:45 PM


 
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Jason
(Login nervoustrigger)
YF12

Sorry if this one is obvious

April 26 2017, 11:55 PM 

But are you sure the hammer spring preload adjuster isn't backing out a little over time? There is a jamnut that keeps the adjustment and it's pretty easy for it to move unintentionally.

 
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John in FL.
(Login gratewhitehuntr)
AR&P

Doubtful, it shot so good and hasn't been messed with in 2 years. Pellgun oil and co2

April 27 2017, 8:14 AM 

I bought a whole hand basket of Daisy .177 pellets on clearance, $1.72 for 500.
Bulk fill co2, we likely ran 4000-5000 through it with no changes.

I had shot 1/2 tube, plus 1/2 refill, a week before and was hitting tallboy cans with heavies at 50 yards.
Then I was shooting squirrels, another 50-60 shots letting the co2 off before the pump arrived.
Just a normal taper off, and the first air fill tapered normally.
Then nothing.

Thanks for pointing it out, I'll locktite after adjustment.
Search says 1.5-2 turns out.

On the topic of tuning, need to tune for a lighter pellet and 15-17LBS would be plenty.
Is there an estimation of required valve travel vs energy in this gun? I have no idea, first time.

Sorry to be such a newb, it's a perpetual affliction..... 🍻
Yes I UTFS....


    
This message has been edited by gratewhitehuntr on Apr 27, 2017 8:27 AM


 
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John in FL.
(Login gratewhitehuntr)
AR&P

POOF it was full. Adjustor already had locktite, lots of preload. No rebuild kit here. nt

April 27 2017, 9:35 AM 


 
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Jason
(Login nervoustrigger)
YF12

May be the valve stem failing

April 27 2017, 10:39 AM 

The valve stems are prone to failure. What happens is the polyurethane seal pushes out of the brass body and all sorts of weird things begin to happen. I've seen wild velocity swings first hand. Typically if you keep using it, it eventually loses the seal and all the gas evacuates.

[edit] I also agree with Anthony's point, I've heard of the stems pushing out as well. That's more likely to describe the problem you're having. [/edit]

Either way, you can replace it with a QB valve stem or one from Roy at Mountain Airhttp://mountainaircustomairguns.com/faq/ The Teflon version is preferred if you will be using it with CO2. It can be difficult to get Delrin to seal reliably at CO2 pressures.

Regarding the hammer spring adjustment, I'm a little surprised the same setting worked satisfactorily for CO2 as well as HPA at roughly twice the pressure. My guess is it was wasting a lot of CO2.

These guns flow like mad so your 15-17fpe target should be easy to achieve on HPA. You mentioned you are considering a bstaley buffer. That works quite well in these guns to bring the power level down to something more modest like that and achieve longer, flatter strings. Looking back at one I set up for a friend, we went with a 14.5fpe tune (middle curve) that yielded 30 shots inside of a 4% ES.

photo FD PCP tune_zpsmq5owj49.gif


    
This message has been edited by nervoustrigger on Apr 27, 2017 10:42 AM


 
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Anthony R
(Login fivestar45)
YF

Here's a place to look

April 27 2017, 10:38 AM 

Pull the valve out of the tube, or just unscrew the front if it can be pulled out. Take a look at the valve stem, my guess is that the stem is being pushed through the valve head. I've had this happen before the result is the striker stroke is reduced to the point that it can't function. The fix, if you use a two part stem is to Loctite the stem to the head the better fix is a Delrin head without a through hole.

 
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John in FL.
(Login gratewhitehuntr)
AR&P

Makes sense. Probably wasting co2, but it's cheap and I'd adjusted the thing to be quiet

April 27 2017, 11:36 AM 

with my ldc and hit with lowe-ish power.
My method of adjustment included (stop laughing already!) shooting on a bright day, and adjusting power up until I couldn't see the pellets anymore.
In my experience this is around 700fps, and it just happened to be quiet and get a bunch of shots, more than I could count without loosing focus.

With a 20LB bottle, and a Ninja as a pony, you could shoot all week.
After that I never gave a second thought to power level, what's a few cents worth of gas?
OK now you can laugh....

Thanks for the graph, it validated my hope to try substituting washers (or some other bit) for O-rings.
3 O-rings sounds prone to deterioration eventually.

I'll look for stem issues.


    
This message has been edited by gratewhitehuntr on Apr 27, 2017 11:45 AM


 
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Jason
(Login nervoustrigger)
YF12

No laughing here

April 27 2017, 2:59 PM 

I get it. Sometimes good enough is...good enough. It's a hobby so we don't have to be obsessive about the numbers all the time.

Doing it most of the time is sufficient happy.gif

My example is a .177 bottle gun I use for gray squirrels. Efficiency isn't very good, something like 1.0fpe/ci, but 100 shots is enough to vanquish an entire neighborhood of them so I just leave it be as long as it continues to put the pellet precisely where asked.

 
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John in FL.
(Login gratewhitehuntr)
AR&P

OK now you can laugh. All it needed was

April 30 2017, 8:26 PM 

1/2 turn more preload. Originally had 1.75 turns, adjusted to 2.5 turns and works good.
It really was valve lock, maybe the hammer spring took a little set... or air pressure smashed the valve a little more.

Funny part is that when I'd first fill it, it'd shoot, but wait 10 mins and the valve would lock. Pop it off a bunch of times and it'd start shooting again, wait and it'd lock again.

I need a more accurate gauge.....

EDIT and BTW it looks like I was already in a good spot with the adjustor, or at least the same range a lot of people found usable, 1.3-2.5 turns is what I see in tune reports.
Close enough was pretty close!!!

Further edit, leak was likely just some crud in the valve. LOTS of crud in there, paint, swarf, pellgun oil all dried up....


    
This message has been edited by gratewhitehuntr on May 1, 2017 11:05 AM


 
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