BAM B40 Galling problem

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PNW1985

PNW1985

Member
Aug 5, 2022
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40
Malo, Washington, United States
My BAM B40 is having a galling problem. I have stripped, re lubed with JM Moly lube in all the right places, and the compression chamber is still galling the main tube. This galling can be seen through the cutout on the underside of the gun. I sanded and polished, which made the first 50 shots run smooth. After that, the galling continued. Any thoughts? The delrin piston bearing on the back side of the piston seems a little buggered up. I don’t think that’s my problem. Could be, maybe? What are your thoughts? I have a tx200 I can shoot instead, but I’d hate to give up on this gun. Guess the clone will never be as good as the original.
 
When you cock the rifle, the foot of the cocking arm pushes the back end of the piston up and into the compression chamber and even lubed, the piston is going to rub on the inside top of the chamber like yours is. It's one of the reasons for that button or in some cases buttons since many use 3, spaced evenly around the rear end of the piston. Another is because that button or buttons help keep the piston better centered in the comp tube.
Someone will come along and explain it better than I did, but if yours is buggered up, I'd replace it.
 
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I'm probably misunderstanding what you meant by delrin piston button thinking you were talking about a buttoned piston, which means I have to learn what the delrin piston bearing you mentioned is...lol.
When you see someone mention "buttoning a piston" it's what they're talking about. Those with the tooling will drill small holes on the outside rear of the piston, superglue and insert delrin buttons sized to fit those drilled holes and stick up just a hair above the piston edge, then once dry, they sand or file them down so that once done, the piston with "buttons" will slide/fit back inside the compression tube.
They stop the top of the piston from rubbing the inside top of the compression tube to help stop the rubbing you're having and they also help to center the piston inside the chamber. Some use delrin, ARH makes piston "buttons" that just get glued on without any drilling, then there's the poor man's "button" which is using a piece of Mt. Dew bottle or similar to glue on there and help do the same thing.
 
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PNW1985 said:
My BAM B40 is having a galling problem. I have stripped, re lubed with JM Moly lube in all the right places, and the compression chamber is still galling the main tube. This galling can be seen through the cutout on the underside of the gun. I sanded and polished, which made the first 50 shots run smooth. After that, the galling continued. Any thoughts? The delrin piston bearing on the back side of the piston seems a little buggered up. I don’t think that’s my problem. Could be, maybe? What are your thoughts? I have a tx200 I can shoot instead, but I’d hate to give up on this gun. Guess the clone will never be as good as the original.
Click to expand...
Hey PNW1985 - please included pics to better understand your situation :unsure: .
 
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It sounds to me as if your delrin piston bearing ring has worn through. I had a similar problem with my B40 and replaced both the front and rear pieces with new units purchased at Pyramid Air ( https://www.pyramydair.com/model-schematic/m/air-arms-tx200-mkiii-air-rifle/174#4072 ). The original bearing pieces used in the B40 did not seem to be as strong as the replacement parts for the TX200. Luckily most of the B40 parts can be replaced with original TX200 parts.
 
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