GTA
Airguns by Make and Model => Vintage Air Gun Gate => Topic started by: DaleLicht on February 15, 2022, 11:31:03 AM
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Hi, I am rebuilding a Benjamin 132 pump pistol and have disassembled the gun, and then cleaned, repaired and reassembled the pistol with new parts and seals from a full rebuild kit. I have taken it apart and put it back together 3xs to make sure everything is correct, but I am still getting very low pressure build up, even with multiple pumps the pressure does not increase over a slight puff out the barrel. I was wondering about the pump piston and what the correct procedure is to adjust the piston length to proper measurements. I read that you should have it as close to the inlet valve as possible, but I was wondering if it needs to be behind the oiling hole to allow air to enter the chamber to be compressed and driven into the cylinder. I would appreciate any suggestions here in regard to next steps to get this pistol shooting around 250-300fps if possible. I do have the the newer valve with the dual outlets so the alignment key is not used when installing the valve. I am also using lead seals instead of the newer Urethane seals that are available.
Thank you for your help in advance!
Dale ;D
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You should have more than a puff of air even with the pump cup not adjusted properly. I would check to see if you have a seal leaking, pump and let it set a few minutes see if any air is left in it.
Adjust pump cup length so that it bottoms out with the pump handle slightly open. When you shut the pump arm you should feel it cam over slightly.
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Yes, when pumping you should see the end of the pump cup go pass the air hole when arm is fully extended. Upon doing this you should hear a “psst” sound as it’s taking a gulp of air. Also, that is not an oiling hole. If your putting excessive oil into that hole it’s flooding the valve. The valve is meant to get oil through it via pumping and shooting. It’s not meant to take a bunch of oil. That much oil sitting in there is not going to be shot outta the valve. The more oil you have in your valve the less air.
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I appreciate your feedback, I definitely had too much oil in the chamber and valve. I actually found the original instructions on line for the rebuild of the piston and valve for the pistol. The doc was very helpful, as it had the exact measurement that the piston assembly should be set at, and the comment that the air chamber and pump chamber should be free of any oil. It also had the correct procedure for the seating of the valve using lead seals. It was a Eureka moment. I am going to post the document in this forum for future Benjamin 132 enthusiasts. I will be performing the rebuild this weekend, and post the results. My real problem is that I have to work and it cuts into my fun time...... ;)
Thank you!
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Yes, when pumping you should see the end of the pump cup go pass the air hole when arm is fully extended. Upon doing this you should hear a “psst” sound as it’s taking a gulp of air. Also, that is not an oiling hole. If your putting excessive oil into that hole it’s flooding the valve. The valve is meant to get oil through it via pumping and shooting. It’s not meant to take a bunch of oil. That much oil sitting in there is not going to be shot outta the valve. The more oil you have in your valve the less air.
So when I reassembled the piston assembly and adjusted to the correct length, the piston cup does not go past the intake port on the chamber. There is no way to adjust the piston head to return past the hole with the lever fully extended. I am confused. Do you have an explanation?
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Please disregard the last post. My bad. I was incorrect. The piston is traveling past the intake port when the lever is fully extended. I am no longer confused. Thanks for your knowledgeable input.
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Please disregard the last post. My bad. I was incorrect. The piston is traveling past the intake port when the lever is fully extended. I am no longer confused. Thanks for your knowledgeable input.
That’s good. I was gonna say you have a bigger problem then.