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Old 08-10-2018, 08:41 AM   #1 (permalink)
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Rebuilding a Benchmark expansion chamber

Got a leak in an old 4 stage, and can't seem to get this thing apart. Noticed a screw while looking into the bottom
1/8 NPT hole that rotates with the piece when I spin it. Assumed I drop an allen key down the hole in the top inlet, but the biggest one that fits does not turn the screw. Anyone know anything about opening these relics up?
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Old 08-10-2018, 10:07 AM   #2 (permalink)
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I believe there is loctite on that screw. I think you need to heat up the bottom to get it loose. Put a steel pipe nipple in the bottom NPT port to get a grip on it. I've only done one a few years ago. There is a big o-ring on that bottom piece that you may loose if you go too hot.
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Old 08-10-2018, 10:49 AM   #3 (permalink)
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Whole thing spins freely. Figured it's how you align it to whatever position you want that exit port.
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Old 08-10-2018, 11:19 AM   #4 (permalink)
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Quote:
Originally Posted by sturmgewehr View Post
Whole thing spins freely. Figured it's how you align it to whatever position you want that exit port.
Right,does the screw head inside turn with the bottom?

Or does the screw go through the bottom? The one I'm thinking of has the screw head inside the body of the chamber.
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Old 08-10-2018, 11:48 AM   #5 (permalink)
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Subscribed because I have a 6-stage exp ch and a 4-stage Intruder exp ch (angled ASA bottom) where I'd like to swap the 6-stage flat bottom onto the 4-stage. Reason being the flat bottom 4-stage Benchmark/PTP exp ch doesn't seem to pop up that often.
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Old 08-10-2018, 11:58 AM   #6 (permalink)
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pretty sure you have to grab the bottom and spin the screw at the same time.
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Old 08-10-2018, 12:47 PM   #7 (permalink)
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pretty sure you have to grab the bottom and spin the screw at the same time.
Yup. There's a long allen head screw that's red loctited in there. In order to get my intruder apart I had to hold the bottom in a vise, apply heat, and then loosen the screw. The top section was also red loctited to the body. I ended up having to sacrifice an old bottom line ASA to get that off. I took a hacksaw and cut a slit bisecting the threaded section of the ASA and then used that to pinch the expansion chamber ASA threads in a vise. Apply heat, not too much because there's a big o-ring in there that looks like it would be hard to find a replacement, strap-wrench, and viola!
Reassembly is pretty straight forward. According to Forest at PTP red loctite is a must. Getting the right tension on the long screw so that it rotates freely but doesn't wiggle just takes a little fiddling around before the loctite sets back up.
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Old 08-10-2018, 02:49 PM   #8 (permalink)
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Right,does the screw head inside turn with the bottom?

Or does the screw go through the bottom? The one I'm thinking of has the screw head inside the body of the chamber.
Yep. You can see the end of the screw poking out inside the chamber when you look through the 1/8 npt port. Screw rotates with the flat base when turned.
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