GTA

Airguns by Make and Model => Vintage Air Gun Gate => Topic started by: mooseracing on August 18, 2014, 08:23:52 PM

Title: Need help understanding a Benjamin 312
Post by: mooseracing on August 18, 2014, 08:23:52 PM
I have a 312 I have been sitting on too long.  I put a repair kit and I am still not building pressure.  When I pull on the pump handle, I can feel a vacuum building, until it gets to the little vent hole.  On the pressure stroke there is less resistance than the vacuum stroke.

Looking at the schematic it seems like the air should be getting into the chamber, but I'm not sure how it would move the big slug/hammer backwards so the trigger can catch it.

Title: Re: Need help understanding a Benjamin 312
Post by: Ckistner on August 18, 2014, 08:36:15 PM
Quote from: mooseracing on August 18, 2014, 08:23:52 PM
I have a 312 I have been sitting on too long.  I put a repair kit and I am still not building pressure.  When I pull on the pump handle, I can feel a vacuum building, until it gets to the little vent hole.  On the pressure stroke there is less resistance than the vacuum stroke.

Looking at the schematic it seems like the air should be getting into the chamber, but I'm not sure how it would move the big slug/hammer backwards so the trigger can catch it.

I'm a little confused.  Are you cocking the bolt before pumping?

Ck
Title: Re: Need help understanding a Benjamin 312
Post by: Gillman on August 18, 2014, 10:30:17 PM
Check out these videos off youtube and it will explain everything about the 312 and how to tear it down and how it functions.

https://www.youtube.com/watch?v=W1_DGNaaAs0 (https://www.youtube.com/watch?v=W1_DGNaaAs0)

https://www.youtube.com/watch?v=fJaYgk9DnEs (https://www.youtube.com/watch?v=fJaYgk9DnEs)

https://www.youtube.com/watch?v=ycrFlCz7I60 (https://www.youtube.com/watch?v=ycrFlCz7I60)

Good luck,

John
Title: Re: Need help understanding a Benjamin 312
Post by: bbv13 on August 21, 2014, 11:44:17 PM
Thanks for the links. I'm fixing to rebuild a 310 and that was helpful.

Bryan
Title: Re: Need help understanding a Benjamin 312
Post by: mooseracing on August 30, 2014, 11:41:09 AM
The cutout video is helpful.  The bolt was missing the screw that cocks the hammer.  Also the valve nut on the one I have has the taper going towards the valve.  I suppose I will take it apart and give everything a good cleaning again and see how it does.
Title: Re: Need help understanding a Benjamin 312
Post by: mooseracing on September 13, 2014, 01:23:19 PM
Backup again.  I polished everything up nice and shiny where the sealing edges rest for the vale but I am not building pressure.  The release stroke has a pretty good vacuum on it, so it makes me think the little seal under the spring for the inlet is sealing up good.  Which makes me then think the Outlet valve isn't sealing or the air is leaking by the Outlet valve body/transfer port?