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Title: Smith & Wesson 77A Valve Tune up - How To
UltimateAirguns   Airgun Tuning and Repair Section
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HiPoCo2
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Rank:Platinum Member

Score: 402
Posts: 402
Registered: 12/21/2008

(Date Posted:12/22/2008 10:55 AM)
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After struggling to get my S&W 77A to function properly, i finally got it dumping 20 pumps and shooting HARD.. When i received it, the gun would only dump 12 pumps..a far cry from the factory rated 20 pumps that it's supposed to dump. Any more pumps than 12 took additional recocking and firing to release the air.

The gun had a few problems inside so with some trial and error troubleshooting I finally got it to work.. Suprmatic also helped me out on it by resealing the valve with Urethane, truing up the front valve on the lathe and he also angle milled the hammer to give it a new surface and improved contact angle.


At first , i thought the hammer spring was just old and worn out so I cut 2 coils off it to increase the hammer drop and also changed the valve spring to a lighter spring, but still it wouldn't dump 20..

Then Suprmatic angle cut the hammer because the hammer might have been hitting the valve extension stem on an angle causing it to bind inside the extension housing.. Still wouldn't dump 20

The Suprmatic Resealed the valve with Urethane and cut a new edge on the small front check valve.. Still wouldn't dump 20..

Then i got looking at even closer and noticed some very slight burring inside the valve extension housing that could cause the stem to bind when the hammer hit.. Well i chucked the extension stem up in the drill press and polished it with 600 sandpaper.. Chucked up the extension housing and internally polished it with 600 paper.. I also drilled out the transferport one size up, it can use it since the stock hole is so small..

Now, i reassembled the gun and VOILA! The Bit!h dumped 20 Cool

Here's an exploded photo of the valve thanks to Suprmatic, i wrote some of the little tune ups i did to the various parts incase you other 77A owners
were having similar problems.




I know this airgun isn't that common but you never know when you'll end up with one or when you might need this. If yours does the same thing this will save you ALOT of time and headaches.

Cool


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notec
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Rank:none
Score:22
Posts:22
From: Canada
Registered:01/11/2009

Re:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:01/11/2009 14:05 PM)

Thanks!! Hope I never have to tear mine apart....lol
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HiPoCo2
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Rank:Platinum Member

Score:402
Posts:402
Registered:12/21/2008

RE:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:01/11/2009 15:03 PM)

well it's not that bad if you're mechanically inclined..  They're a rugged airgun so it's not like you need to be tearing it apart all the time..   But if it does start to act up on you this is where to come... Have you chrono'd yours? how many pumps will yours dump? 


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notec
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Posts:22
From: Canada
Registered:01/11/2009

RE:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:01/11/2009 15:19 PM)

Yup, using Crosman .22 pointed
                  PUMPS                                       FPS
                    10                                            530
                    15                                            576
                    20                                            600
                    25                                            620
                    30                                            700 
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JG1966
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Posts:4
From: USA
Registered:02/04/2009

Re:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:02/05/2009 15:07 PM)


Hello HiPo,

                           Interesting site you have here. I am working on a 77A for one of the guys at work. It is a very interesting rifle since I am more use to the crosman type guns. Always nice to see something a little bit different. I have the valve out because it is leaking. I replaced the pump piston seal with a crosman 1400 and it works good but like I said the valve is a leakin, The valve is sitting on the bench right now and I am looking at the pins that have to be removed to get the valve apart. Any suggestions on the best removal process? Also it sounds like your buddy did some good work on the valve.... did you replace the stem and seal with a urethane rod type seal or or just replace the seal in the brass cap seal holder? If you just replaced the stock stem seal that is pretty cool.... kind of wondering if I could get this done to my valve?. Anywho nice site and good luck with it.

                                                   John
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HiPoCo2
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Rank:Platinum Member

Score:402
Posts:402
Registered:12/21/2008

Re:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:02/06/2009 21:57 PM)

 JG1966,  you will need a small screw with the same threads as the pins..  What you can use is one of the brass or metal standoffs used for securing computer motherboards to the case.. There are different type standoffs with different threads.. I got lucky the first time and found one.. Or you can get your some fine thread machine screws to thread in the pins so you can pull them out.

The stem seal will have to be machined out and new one pressed in. The seal in mine was replaced, pressed back into the brass cap seal holder.     How bad is your stem seal now?  Can you take some clear closeups of the parts?  Sometimes they can be resurfaced with some very fine lathe work..


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From: USA
Registered:02/04/2009

Re:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:02/07/2009 04:21 AM)

Unfortunately I am behind the times... I dont have a camera. Actually my phone has a camera but geting a good pic would be fruitless. I havent taken the valve apart yet been doing other things but maybe this weekend I will.  Or maybe I can just send the valve to get resealed. Just need to know where to send it hehe.

                                     John
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HiPoCo2
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Rank:Platinum Member

Score:402
Posts:402
Registered:12/21/2008

Re:Smith & Wesson 77A Valve Tune up - How To
(Date Posted:02/07/2009 09:34 AM)

 Well if the rifle is worth something to the owner I would go the extra mile and have it resealed with polyehtylene if possible.. Why not try contacting Roy at MountainAirCustoms, he might even be able to make a stem from teflon for the rifle, a bunch of us are running his stems in our guns and they're great.. they'll also last a lifetime..

Never know ,  it won't hurt to ask..  

I know of a local guy in my area that can reseal them, he's actually part of this forum..


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