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PostPosted: Mon May 30, 2016 10:14 am 
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Joined: Sun Nov 30, 2014 8:22 pm
Posts: 286
Location: Hill Spring, Alberta
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The first photo is from the front of the piston and the other two from the rear. I've sanded the piston so I could see the cracks.

In the 2nd photo you can see where bits of metal beside the crack appear to have broken away and that's what caused the galling.

Luckily, damage to the action is confined to the non-compression part of the cylinder and I'll just sand and hone it out.

I've ordered a replacement from R&R and Rob has it in stock so I'll soon be back in business. :D

Peter :D


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PostPosted: Mon May 30, 2016 4:17 pm 
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Joined: Thu Feb 02, 2006 11:35 pm
Posts: 3099
Location: Alberta Canada
One, reasoning comes to mind is poor quality metal. Second, reason would be too small of pellet head size to have a good seal within the bbl responding like that of near dry firing. Back to poor quality metal contributioning to a linear crack. Thirdly, slightly too small seal dia resulting in near dry firing once again. And as you say the gun has fired thousands of pellets, metal fatgue would be the common denominator here. Either way you caught it in time before serious tube damage could occur.

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PostPosted: Mon May 30, 2016 5:08 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1278
Location: United States
Thanks for posting the pix. It isn't as bad as I had imagined, I pictured it opening up enough to be a snug fit in the receiver. They often have metal shavings/splinters in the guns when new so it's possible the crack wasn't the source, but who knows. My guess is that's more or less how it looked when it left the factory but I guess we'll never know. I might continue to use it as-is, or maybe weld in a few spots, but that's entirely up to you. I would also button the piston, which if done from day one might have prevented the scraping/grinding. Can't lose by using buttons, they're a win win mod.


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PostPosted: Mon May 30, 2016 6:45 pm 
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Joined: Sun Nov 30, 2014 8:22 pm
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Location: Hill Spring, Alberta
I suppose the crack could have always been there and I just didn't see it until the galling occurred but I think I would have noticed it during the lube tune.

Rob at R&R concurs that it is likely just poor metal which fatigued. He has the pistons in stock and is sending me one.

I tried to button it when I did the lube tune but the plastic off a 2L Pepsi bottle is too thick for this particular piston/cylinder and there's insufficient clearance. Maybe I'll try some plastic off a water bottle. It seems thinner.

Peter :D

PS: I tried to send pictures to Crosman just for their information, but their "contact" facility is down for repair or maintenance or something.


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PostPosted: Tue May 31, 2016 12:02 am 
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Joined: Sat Jan 25, 2014 9:16 pm
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Location: United States
Hard to say what happened I spoze, but I still believe it was a poor weld since both cracks appear right on the weld lines. Fyi you can use the 2-liter bottle plastic, you just have sand it to the right thickness after install. The stuff I use is .0075 thick and I always have to sand it in a Crosman. How much varies but the one I have sitting here is ended up at .005". 2-liter is ~.015 +-.003. It also helps to open up the end of the receiver a bit since they're typically tighter at the aft end. You don't want buttons that are .001 plus .001 of glue to fit that tight spot, too thin.


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