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 Post subject: Main spring i believe
PostPosted: Mon Jun 02, 2014 4:07 pm 
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Joined: Mon Aug 05, 2013 4:35 pm
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Location: Fredericton, NB
greetings

thought i run this by a few of you experienced tinkerers, my Browning Leverage which has shot about 7000 pellets reliably and accurately has started to have a shifting POI, it all started at the beginning of this shooting season, it does this every 50 pellets or so(on average) and is preceded by a dull "thud" where the pellet either goes completely off target, or simply does not get out of the barrel, then the POI shifts down about 2 inches, and either left or right, and it stays there unless i re-zero the scope

i believe i'm dealing with a broken main spring, on the Chrony; the ES has gone up by 10 fps, and the speed has dropped by 30 to 40 fps overall

i'll only know when i take it apart, and take the opportunity do a tune at the same time

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PostPosted: Mon Jun 02, 2014 4:27 pm 
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Location: Kingston, ON
They are pretty easy to work on.
I believe I clipped a few coils of my mainspring shortly after I got it.
You have to remove the thumb tab off the anti-beartrap, then concoct a spring compressor to fit the plastic hook at the rear, but otherwise pretty straightforward bits inside.
PM me if you have questions.
Duke.

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PostPosted: Mon Jun 02, 2014 5:44 pm 
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Dukemeister wrote:
They are pretty easy to work on.
I believe I clipped a few coils of my mainspring shortly after I got it.
You have to remove the thumb tab off the anti-beartrap, then concoct a spring compressor to fit the plastic hook at the rear, but otherwise pretty straightforward bits inside.
PM me if you have questions.
Duke.



thx Duke

i already used your first tip of taking off the anti bear trap knob, decompressing the spring was relatively easy, i just used a heavy winter jacket on the back end and tapped out the pin...i can now tell you its not the spring, its in one piece(pic below), the only thing is that it seems a little bent in the middle, its noticeable when i turn it in my hands, i'll take a closer look at the piston seal and breech seal once i figure out how to take the piston out, i have a feeling i'll have to take the trigger group out........i'll pm you if i hit any snags, thx again bro


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PostPosted: Mon Jun 02, 2014 7:10 pm 
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is this bent spring going to a problem, do i need to swap it :?:


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PostPosted: Mon Jun 02, 2014 8:36 pm 
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I doubt it. Every gun I have stripped down has a bent spring, and they all work fine. I once owned a ruger air hawke that did the same thing as you describe. Im sorry though that I never found out what caused it. However I wonder if heat buildup could expand the compression tube enough to get blow by ?

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PostPosted: Mon Jun 02, 2014 9:20 pm 
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When I replaced the spring on my phantom, I was amazed at the amount of crud that had accumulated in the hole at the bottom of the cylinder. Was it dried up production grease, blow-back from from dirty pellets, combination of both...I got no idea, but it was hard stuff.

Perhaps yours has clogged up a bit as well.


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PostPosted: Tue Jun 03, 2014 2:27 am 
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Location: Halifax, NS
I do not have a Browning but I'd look for metal galling or wear on the insides ..seems like it catches at times, a proper de-grease & re-lube may not hurt either.
roger r. is on to something about lead dust blow back slowly building up around/in the transfer port. I think it would cause a gradual decline of FPS Instead of an erratic shot cycle every 50 shots or so. I started cleaning the face of the transfer port with a Q-Tip dipped in nail polish remover years ago, when I noticed that every 50 + shots there would start to develop a light ring around the transfer port - wasn't long figuring out that it was lead dust.
Btw: have you checked the compression seal yet ?

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PostPosted: Tue Jun 03, 2014 3:00 pm 
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well after giving the internals a de-greasing, i found the piston seal to be in good shape, the piston skirt itself has two wear marks, one on the bottom of the skirt, and a corresponding mark near the seal(difficult to see on pic, see arrow), seems something has created friction, both marks line up with the cocking slot of the skirt :?

unlike other chinese units i've taken apart, the amount of grease in there was minimal, there was however a mess around the piston seal itself which opens the possibility of blow by, or even other problems

i ordered a rebuilt kit which includes a spring and seals, i wanted to eventually PAL that rifle anyway, add to this a complete deburr and polishing of all components, whatever it was, should be gone

the left over spring can go in my airhawk since they use the same one


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PostPosted: Tue Jun 03, 2014 3:13 pm 
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If there is wear on the piston there could be wear or galling on the inside of the comp tube, may need a light to inspect.

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PostPosted: Tue Jun 03, 2014 4:04 pm 
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GoodEnough wrote:
If there is wear on the piston there could be wear or galling on the inside of the comp tube, may need a light to inspect.


just inspected the inside of the compression sleeve, there is scoring on the bottom part as it corresponds with the marks on the piston skirt, but its very minor, in fact, i can't even feel it with my finger, so its really on the surface, a quick sanding inside with 1500 grit will certainly take care of that

as you can see from the pics, the piston doesn't go in all the way, so the mark on the bottom skirt is a mystery, don't think its the spring as it would be making contact inside, i also noticed a bit of scoring on the seal itself, also lining up with the other wear marks, i ran the piston up and down and it shows the right amount of resistance, if i cover the transfer port with my finger, i can't pull up or push down so i know its still sealing, however, when it is pushed by the main spring, its possible it might be squeezed on one side and allowing blow by on the top....that's my theory anyway :wink:


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sleeve and piston.JPG [ 294.26 KiB | Viewed 1175 times ]
sleeve.JPG
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PostPosted: Sun Jun 08, 2014 4:17 pm 
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Sorry man, I don't know the internals or actual movement of the action or the piston design, from the pics I can only guess. I am wondering if you can button that piston.
Seem as if the piston may be a tad too loose in the sleeve causing the pressure from the cocking arm to cant it inside & then the piston fish tails as it slams home for shot completion & catches somewhere during that travell specially if lube is scarce.
Or that the compression tube was not true & linear forces have caught up. Can't really tell just guessing. But If you can button the piston that might help.
A new piston may end up the same if the comp tube is wonky.
BTW: lots of info on springs on the net, wire guage, ID / OD of the spring, distance between coils, number of coils, amount of preload, most people think bent/warped main spring are okay. You may find it not so ;)

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PostPosted: Sun Jun 08, 2014 4:27 pm 
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The seal at the front of the cylinder to the barrel goes on a regular basis on Chinese rifles. Most of them use the same seal.
Can drop up to 100 fps from leakage there alone.

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