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PostPosted: Fri Nov 15, 2013 11:48 pm 
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After seeing Woody’s chrony numbers I went back and checked my piston o-ring just in case and didn’t see nothing wrong with it, so I asked myself what more could I do to this gun to squeeze out some more fps .

With some further investigation, while I was looking down the air transfer hole, I noticed that the tip of the valve stem head protrudes into the air path therefore restricting some of the airflow.

I disassembled the gun and removed the valve stem and sanded the end down as much as possible without it having any effect on the o-ring lip, I could have gone a little more but figured it was enough to clear the path of flow.

Please do not do this mod if you’re not comfortable with the trigger assembly it’s a little tricky not hard but tricky.

I also cleaned the barrel and did a quick barrel re crown. :wink:

Some number:
before with the grizzly 8.6gr 340fps after adding extra tap 389fps with the two mod's 404.2fps.
after adding extra tap mod with the RWS super H 6.9gr 427fps and after second mod 451.3fps :D

grizzly 8.6gr
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RWS super H 6.9gr
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valve pin before.
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pin and piston with tape
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pin after
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3 shot group 5m 8.6gr grizzly's
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second 3 shot group same 8.6gr pellets.
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PostPosted: Sat Nov 16, 2013 12:06 am 
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That's pretty good Ace, been thinking about one of those P17's but I read someplace that there had been a few piston issues.
Has anyone had problems at all with this pistol.

Anyway nice job of figuring out how you can get a bit more out of the gun.

Joe

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PostPosted: Sat Nov 16, 2013 12:16 am 
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It appears the vast majority of your gain was from the piston mod, not so much the stem profiling (389 vs. 404fps, or roughly 4% from the stem re-profile). What is it you stuck on the end of the piston and what was the overall length of the piston housing once the shims were installed?

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PostPosted: Sat Nov 16, 2013 12:51 am 
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your correct the majority of the gains came form the piston mod but i definitely got something for the stem work not much anywhere from 10 to 20fps.
Its aluminum tape you see on piston it would have looked a lot nicer if i had something to cut all them Little circles perfectly :lol:
sorry cant give you a number i haven't measured the total length maybe the next time i have it apart.

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PostPosted: Sat Nov 16, 2013 5:17 am 
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Ace wrote:
your correct the majority of the gains came form the piston mod but i definitely got something for the stem work not much anywhere from 10 to 20fps.
Its aluminum tape you see on piston it would have looked a lot nicer if i had something to cut all them Little circles perfectly :lol:
sorry cant give you a number i haven't measured the total length maybe the next time i have it apart.


Ace, how many layers of aluminum tape did you stick on?


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PostPosted: Sat Nov 16, 2013 10:59 am 
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HW777 wrote:
That's pretty good Ace, been thinking about one of those P17's but I read someplace that there had been a few piston issues.
Has anyone had problems at all with this pistol.

Anyway nice job of figuring out how you can get a bit more out of the gun.

Joe

Just buy one! If it goes out, it seems to be a simple repair that would subsequently require no further attention. If you're lucky, you don't need to do anything at all and this should actually be the more likely situation.

I got mine 3 or 4 weeks ago, haven't done anything to it and it has been great out of the box for I guess 600 pellets at least. Absolutely superb for the $45 I paid (with red dot - removed and using iron sights).

Thanks for the mod documentation, Ace. I'm happy with my P17 as it is, but if the o-ring ever wears out, I will pad out my piston while I have it apart for repair.


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PostPosted: Sat Nov 16, 2013 4:14 pm 
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gctkaz wrote:
HW777 wrote:
That's pretty good Ace, been thinking about one of those P17's but I read someplace that there had been a few piston issues.
Has anyone had problems at all with this pistol.

Anyway nice job of figuring out how you can get a bit more out of the gun.

Joe

Just buy one! If it goes out, it seems to be a simple repair that would subsequently require no further attention. If you're lucky, you don't need to do anything at all and this should actually be the more likely situation.

I got mine 3 or 4 weeks ago, haven't done anything to it and it has been great out of the box for I guess 600 pellets at least. Absolutely superb for the $45 I paid (with red dot - removed and using iron sights).

Thanks.......guess for $50 it's worth a try

joe

Thanks for the mod documentation, Ace. I'm happy with my P17 as it is, but if the o-ring ever wears out, I will pad out my piston while I have it apart for repair.

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PostPosted: Sun Nov 17, 2013 9:33 am 
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gctkaz wrote:
HW777 wrote:
That's pretty good Ace, been thinking about one of those P17's but I read someplace that there had been a few piston issues.
Has anyone had problems at all with this pistol.

Anyway nice job of figuring out how you can get a bit more out of the gun.

Joe

Just buy one! If it goes out, it seems to be a simple repair that would subsequently require no further attention. If you're lucky, you don't need to do anything at all and this should actually be the more likely situation.

I got mine 3 or 4 weeks ago, haven't done anything to it and it has been great out of the box for I guess 600 pellets at least. Absolutely superb for the $45 I paid (with red dot - removed and using iron sights).

Thanks for the mod documentation, Ace. I'm happy with my P17 as it is, but if the o-ring ever wears out, I will pad out my piston while I have it apart for repair.


It's almost guaranteed that your o-rings will wear out, so just plan ahead and buy some in ahead of time. Get 90 dura for the valve.

I detuned mine by drilling holes into the end of the piston to increase the residual volume because I couldn't get through a 60 shot practice without fatiguing my arms :) I'm thinking I should get another and try taking it the other way just for fun. p17 still has the nicest trigger of any of my pistols - it's a great design, and the moving mass is pretty minimal.


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PostPosted: Sun Nov 17, 2013 8:23 pm 
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I think I'll try using JB weld on the piston instead of tape and see if that works. I can always gring it off if it doesn't work out.


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PostPosted: Sun Nov 17, 2013 10:34 pm 
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Jaker wrote:

Ace, how many layers of aluminum tape did you stick on?

I have 12 on mine but i haven't checked the fps yet.


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PostPosted: Sun Nov 17, 2013 10:47 pm 
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Plasticman wrote:
I think I'll try using JB weld on the piston instead of tape and see if that works. I can always gring it off if it doesn't work out.


I wouldn't use JB weld if i where you, the tape method is much better and safer because you can slowly add layers to it as for the JB weld if you have to much you will brake something on the gun.

Remember there is very little head space between the piston face and the air inlet face.

I know that around 12 stripes of tape is safe, and you will/should feel a stiffer pump stoke.

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PostPosted: Mon Nov 18, 2013 12:08 am 
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So I take it that the piston mod works like a cars cylinder head combustion chamber
If you make the space smaller it compresses the air more
Adding the tape effectively reduces the amount of space that the same amount of air gets crammed into
Can all pneumatics be modified this way?
Adding psi into a cylinder head will also increase the pressure in that space which requires better head gaskets, do the piston seals need to be modified in the case of an airgun?

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PostPosted: Mon Nov 18, 2013 12:44 am 
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Ace wrote:
I wouldn't use JB weld if i where you, the tape method is much better and safer because you can slowly add layers to it as for the JB weld if you have to much you will brake something on the gun.

Remember there is very little head space between the piston face and the air inlet face.

I know that around 12 stripes of tape is safe, and you will/should feel a stiffer pump stoke.


The best bet would be to use something like a tape (note, different tapes will have different thicknesses, so 12 layers may not mean anything to someone else) to find the optimum output, measure it, then something like JB Weld could be used and filed/sanded as appropriate to the correct height (matched to the prior height of the tape). Something that hasn't been mentioned- what happens when that tape starts to peel away inside the tube (it will at some point)? Jams? Damage?

Frankly, I think the best possible solution would be soldering- i.e. silver solder once the correct height has been determined using something like the tape. Mind-you, this then becomes a fair amount of work for a $50.00 pistol.

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PostPosted: Mon Nov 18, 2013 2:50 am 
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Or possibly machining and oversized head. Give it the customer to fit. When all that is done you could make several of these pistons up for sale.

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PostPosted: Mon Nov 18, 2013 10:29 am 
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AirGunEric wrote:
Ace wrote:
I wouldn't use JB weld if i where you, the tape method is much better and safer because you can slowly add layers to it as for the JB weld if you have to much you will brake something on the gun.

Remember there is very little head space between the piston face and the air inlet face.

I know that around 12 stripes of tape is safe, and you will/should feel a stiffer pump stoke.


The best bet would be to use something like a tape (note, different tapes will have different thicknesses, so 12 layers may not mean anything to someone else) to find the optimum output, measure it, then something like JB Weld could be used and filed/sanded as appropriate to the correct height (matched to the prior height of the tape). Something that hasn't been mentioned- what happens when that tape starts to peel away inside the tube (it will at some point)? Jams? Damage?

Frankly, I think the best possible solution would be soldering- i.e. silver solder once the correct height has been determined using something like the tape. Mind-you, this then becomes a fair amount of work for a $50.00 pistol.

when i said tape i meant the aluminum foil tape that I'm using :wink:

Eric this aluminum tape really sticks well especially to itself i doubt it very much it will come off unless you deliberately peel it off even then its very hard to do, I first cleaned the piston head of any oil or residue with a some acetone for optimum grip of the tape. if you've ever worked with this tape you will know what I'm talking about when i say this stuff sticks well. :wink:

JB weld would be to much work IMO, not to practical in this case.



rrdstarr wrote:
Or possibly machining and oversized head. Give it the customer to fit. When all that is done you could make several of these pistons up for sale.

Rick what would be really be cool is if you could make one of these, it will become a multi pump.
http://www.network54.com/Forum/275684/m ... roke+PICS-

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