Author Topic: flat pistons/valves?  (Read 9510 times)

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Offline Daysailer

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Re: flat pistons/valves?
« Reply #15 on: May 27, 2011, 03:11:49 PM »
Saico,  you mean like the 5 min reface and less than $5 spent to gain
70 fps at 10 pumps on my otherwise stock 1377 ?

http://www.crosman-air-pistol-owners-forum.com/board/index.php?topic=3688.0
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Offline SaiCo

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Re: flat pistons/valves?
« Reply #16 on: May 27, 2011, 10:51:00 PM »
Saico,  you mean like the 5 min reface and less than $5 spent to gain
70 fps at 10 pumps on my otherwise stock 1377 ?

http://www.crosman-air-pistol-owners-forum.com/board/index.php?topic=3688.0

Aye! I've always pondered the "solution" of ft valves and pistons. Different strokes, I guess, lulz. I think if I did that drill bit mod, instead of buying an adjustable piston, my pistol would be a lil lighter. BUT I still have a cup seal, not an FT.
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Offline Daysailer

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Re: flat pistons/valves?
« Reply #17 on: May 28, 2011, 12:52:57 AM »
The advantage of the FT piston/valve is the reduction of headspace losses,  where all the air pumped
does not get into the valve.

When doing the valve cone slight trim, the headspace losses of the cup/cone systems is also
eliminated. see pictures :
http://www.network54.com/Forum/275684/thread/1211140448/1211339438/some+interesting+valve+stuff+for+pumpers+%28Pics%29

By filing about .040" off of the tip of the valve cone, the misfit cup/cone is corrected.
Add a washer to the cup holder and an 0-ring to shim as shown in my thead, and all of the
advantages of Flattopping is realized up to about 8-10 pumps, and I have can buy more pellets.

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Offline arkmaker

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Re: flat pistons/valves?
« Reply #18 on: May 28, 2011, 03:44:25 AM »
Nope, not how I see it.  You don't quite gain as musch as a Flat top. Think about it. When you flat top piston and valve, you gain the amount (length) of the cone on your pump stoke.....which equals more air per pump pushed into the valve. right?
More air = more power if you follow up at the other end of the valve to release it efficiently. That's what I'm thinking.
Rich
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Offline eric

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Re: flat pistons/valves?
« Reply #19 on: May 28, 2011, 04:46:33 AM »
nope, you need to l e n g t h e n the piston to accommodate for the space of the cone or else you will still have headspace (the length of the cone).some folks think that a cone piston can be as effecient as a flat top but i have had a alloy (solid) piston ,an adjustable piston (both cones) and a flat top piston .the flat top would cause valve lock at 30 pumps where as the other two it wasn't happening
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Offline Daysailer

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Re: flat pistons/valves?
« Reply #20 on: May 28, 2011, 06:43:12 AM »
ark and eric,  
Both good points about the cone tunnel headspace.  There are threads here and on
the Crosman Forum that also discuss that issue.  Some posters have reduced that tiny amount
headspace by reducing the inside diameter of the port.  The proof for me is the pump
handle rebound from the unstored headspace air when cracking open the handle.
I am now getting 3.5" less rebound caused by unstored, headspace air.

I am not trying to say the method I am trying is ultimately better than a properly
adjusted, and quad ringed FT set up.  However I am very surprised
how much improvement can be gained with the cup/cone, and stiffend stock piston.

I am just trying to point out another, seemingly lost, idea on how to also improve the
pump/valve system with fewer $$$ spent.  

I value your helpful input. Tks
« Last Edit: May 29, 2011, 05:58:50 PM by Daysailer »
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Offline arkmaker

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Re: flat pistons/valves?
« Reply #21 on: May 29, 2011, 02:03:57 AM »
ark and eric, 
Both good points about the cone tunnel headspace.  There are threads here and on
the Crosman Forum that also discuss that issue.  Some posters have reduced that tiny amount
headspace by reducing the inside diameter of the port.  The proof for me is the pump
handle rebound from the unstored headspace air when cracking open the handle.
I am now getting 3.5" less rebound caused by

I am not trying to say the method I am trying is ultimately better than a properly
adjusted, and quad ringed FT set up.  However I am very surprised
how much improvement can be gained with the cup/cone, and stiffend stock piston.

I am just trying to point out another, seemingly lost, idea on how to also improve the
pump/valve system with fewer $$$ spent. 

I value your helpful input. Tks

Don't get me wrong, your method is a fantastic mod, no doubt about it. For me, with access to a lathe and mill, it seems like more work than making the Flat-top piston and facing off the valve. Maybe not, but it seems like it. I guess I'm a FT snob  :P  ;)

I don't even own a chrony yet, but I can tell you that the difference between stock and FT is huge and very noticeable. I'm thinking that with the gain you acheived, that you really don;t need a chrony to see and feel the difference either??

Rich
I Am A Natural Mad Air Gunner  -  Full Of Hot Air & Ready To Expel It Quickly!

114 Rifle, 2240XL Pistol, 1861 Shiloh Pistol, 357 Pistols, Titan GP Rifle, PM66 Rifle, 2400KT .177 LW Carbine, CZ T200 Rifle, Benjamin Discovery .177 Rifle, Hammerli 850 Air Magnum in .22

Offline Daysailer

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Re: flat pistons/valves?
« Reply #22 on: May 29, 2011, 05:57:41 PM »
Without the Chrony, the only difference I would notice is the change in
holdover for my longer pinking ranges.  And that would take a while to
prove with my questionable skills   ;)  I do notice a bit more penetration
in my duct seal indoor trap too.  Chrony really helps with solid proveable info.

With my 1st round of changes, piston stiffening, valve refit, and moving the
trigger spring to the valve, (read it recommended here somewhere) the 1377
pumped harder but chrony'd about 10fps lost.  I was bummed. 
When I went back in and put a hardware store lighter spring in the valve,
it pumped half as hard and gained 20 fps.  Got the rest of the gain when
with the other mods listed on my post.
   
Without the Chrony, I may have believed the power was up, from the harder
pumping supposedly getting more air in. Turned out the opposite was true.

Wish I had your tools and skills with them,  I would agree your method would be
easier.   But I am a hand tool + dremel wizard at making 'one-off' parts for
my sailboats and other mods in my hobbies.  So my efforts here have been to
see how much can be done with the least.  The Mellon and AC FT stuff is really
inexpensive enough to be affortable, and would deliver known improvments.
But my need to reinvent the hexagon wheel drives me to satisfy my maddness...
...  ( i guess buying a Chrony and going cheap on parts is a bit 'out-there' huh  ??? )
Adjust the wind, we cannot.....Adjust our sails (or windage), we should.