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PostPosted: Thu Apr 09, 2015 8:15 am 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
I started a new topic as I was not sure if somebody would see my question if it was embedded in the previous one.

topic67456.html

I was able to reseal the piercing unit and pressurized the pistol.

I should have paid attention to what happened, two evenings ago, when I tried it. It stopped shooting and when I remove the piercing knob I had a bit of CO2 released.

This should have clued me that I probably had an obstruction where there is the small filter in the frame.

This is the only component that I didn't remove as I was not sure how. There was probably some crud accumulated over the year and my glass beading operation was likely NOT the best thing to do. Before reassembly I had cleaned up all the grit (or I thought so) but there might have been tiny particles that I didn't catch and they collected in the filter during my first shooting session.

In short, yesterday, after it was pressurized, I dry fired it a few times but it didn't seem loud. After a few more shots it stopped. I removed the hammer and with a punch pressed on the tip of the valve. No escape of CO2.

So there is probably an obstruction and all the pressure is in the handle. I have never release the piercing knob with a full cartridge pressure as I normally exhaust all of the CO2 before doing it.

I would like to know if somebody has done it before. Does the knob reach a point where the thread are still engaged and the pressure can escape.

This is critical information as I don't want to have the last few threads stripped out and the knob flying away.

If I am successful in releasing the pressure following the suggestions you may give me, I will need to clean the filter. How should I remove it from the frame?

Thanks.

R-Gun Pete


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PostPosted: Thu Apr 09, 2015 9:23 am 
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Joined: Thu Feb 02, 2006 11:35 pm
Posts: 3099
Location: Alberta Canada
Depending upon your seal, it will be down to the last threads befire you get a whisp of Co2 leakage. IMHO place the gun in a vice and with gloves and safety glasses. Unscrew the retaining nut assy carefully and bleed off the Co2.
As for the screen removal, dental picks to remove the star retaining washer. Then fully strip the gun down for a washing of compressed air and some brakleen. Play safe.

_________________
May the cry of the pack be with you upon your hunt

Whitewolf


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PostPosted: Thu Apr 09, 2015 10:30 am 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Thanks Whitewolf!

I will give it a try tonight.

R-Gun Pete


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PostPosted: Sat Apr 11, 2015 10:59 am 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
So, after releasing the CO2 through the piercing cap (because the pistol didn’t want to shoot at all) and spending one hour trying to get out the retaining star that hold the fine screen, I discovered that the cause of the non-firing was not a plugged screen as I first assumed.

It was evident because there was a big hole in it. I also checked my other Mark I and effectively it has a hole too. I then decided that I would not re-install it.

Since this potential cause was out of the way, I recapitulated what I did.

I resealed the pistol using the black o-rings from my Princess Auto kit as I did for a couple of Crosman T-38.

I know that some o-rings will swell in presence of CO2. When they are captive in a groove it means that they even seal better. In the case of the Mark I, I used one for face sealing with the face of the valve.

This was the culprit. I came across some pictures of repairs on the web and it seems that it is a flat seal that is a harder plastic (and not an o-ring) that should be used.

When I started, the o-ring was not swollen so the end of the shaft that is hit by the hammer was sticking out enough. After being exposed to the action of the gas (toward the end my shooting session), it started to shoot weaker and finally stopped. Now, I know that the end of the shaft was not sticking out anymore.

A solution, to make a homemade seal that works better and is not subject to swelling, is to use a plastic cover from a coffee can or a Nestle Quick Can. It is smooth, slightly flexible and also the thickness is not too bad).

The trick is to have cutting punches of the right sizes (Princess Auto again) and to center the small hole for the pin so it is concentric with the outside.

After applying a thin coat of silicone grease to the shaft and the plastic seal, it worked perfectly.

I was able to finish setting the sight and had an enjoyable shooting session with my new (old) toy.

R-Gun Pete


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PostPosted: Sat Apr 11, 2015 11:15 am 
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Joined: Sun Feb 10, 2013 1:16 pm
Posts: 1787
Well diagnosed and fixed! I think that one would have sent me around the houses a few times trying to work out what was happening. I'll have to remember coffee can lids as a source of useful plastic.

Jim


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PostPosted: Fri Apr 17, 2015 12:16 am 
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Joined: Mon Sep 03, 2007 7:56 pm
Posts: 173
Location: Sidney, BC.
Hello.....you are referring to the flat seal of the valve stem.....those are not "o"rings.
and as you've seen they will swell up. You can do as you did or buy a new stem from Eric or any other shop.eg..Gravel or Precision Pellet in the states....KEN.


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PostPosted: Fri Apr 17, 2015 2:23 pm 
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Joined: Tue Oct 18, 2011 12:21 pm
Posts: 431
Location: Ontario
Hi Ken!

Thanks for your comment. This is a good suggestion.

I am aware that some sealing kit are available (for now) so I keep the idea as a last resort measure if nothing else works.

Since I am starting to have a fair amount of "older" airguns, my first interest is to be able to fix them using common components easily available.

The problem with the kits is that they could disappear at any time. On the other hand, if a homemade repair can be done, this means I would be able to replicate it 10 or 20 years down the road.

This being said, it is the piercing assembly that is giving me a hard time. It has the push button type and I cannot remove the rolled pin that locks it so I changed the o-ring for the piercing needle, from the other side, after removing the locking start and slotted washer. It worked fine one day and leaked like crazy the day after.

I am in the process of designing a 2 pieces piercing knob (solid one piece body and a pointed set screw as the piercing pin) that will have only a single set of o-ring (the large one above the 7/8" - 20 thread). The first prototype seems to be working well after refining the shape of the piercing pin.

This solution will solve my problem for a very long time and it could be used with either of my two Crosman Mark I which makes me happier.

R-Gun Pete


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PostPosted: Sun Apr 19, 2015 1:02 am 
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Joined: Mon Sep 03, 2007 7:56 pm
Posts: 173
Location: Sidney, BC.
Sounds like you might have gouged the piercing body slightly? Those little roll pins are tight but they will come out........There is almost always a home made way to fix things but really the parts for the MKI / II are quite reasonably priced and available, not everybody has them... The best O-ring seals for that application are urethane. They will not swell from CO2.....The Crosman MKI/II are great pistols....they also have an adjustable trigger!...KEN.


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