Friday, August 8, 2008

Benjamin 317 Rifle, New Seals

Now to put it all back together...

I made a new lead seal using the technique I've used before for shim washers.
I was lucky enough to have some lead sheeting that was within .004" of the thickness of the original.

I dug the old seal material out of the inlet and exhaust valves.

I used a dowel pin to get the cup walls straight.

The brass cracked a bit, probably would have been a good idea to anneal them first.

The dowel pin has a through hole so I could fit the valve stem inside.

All cleaned up.

New seals from 80 durometer polyurethane rubber.

I made a crimping tool, bored to fit over the rubber seal.

Used a 1/2" ball end mill to make a radius on the inside edge.

The tool.

Crimped the cups. Notice that it distorted the inlet valve seal...

Which leaked upon reassembly. It took a while to figure out why, but when I did I decided to just turn up a solid teflon inlet valve. Sealed perfectly. I think the inlet valve spring just didn't have enough force to seat the harder urethane against the seat, or the deformation induced by crimping the seal threw off the seal surface. Or a combination of the two.

When reassembling I found that I needed to trim the length of the square end of the wrench to just under the thickness of the valve nut. Otherwise it's nearly impossible to get the nut started.
Another lesson learned.

So, how does she shoot?
I did some quickie chronograph shots
2 pumps: 395 fps
3 pumps: 480-500 fps
5 pumps: 600 fps
7 pumps: 675 fps
8 pumps: 695 fps

The valve does not dump all the air though, so you can get followup shots.
With 3 pumps, you can put another 2 pumps in and get almost the same fps
With 5 pumps, no extra pumps gives you 300 fps, one extra pump gives you about 400 fps
With 7 pumps, you get a followup shot at 440 fps
With 8 pumps, you get a second shot at 510 fps.

The manual implies this is normal, "Usually all of the air is not discharged when firing and fewer pump strokes will be needed for recharging."

Anyway, it's wonderful to have it working.

Wednesday, August 6, 2008

Benjamin 317 Rifle Disassembly, Part 4

Now to pull the valve...

The valve is pulled!

The inlet valve spring, washer and the exhaust valve spring.

The exhaust valve, lead seal. The lead seal has an alignment ear that I don't see on the replacement seals offered on gunbroker. Probably doesn't need it. I dug out some lead sheeting and will just make an earless one.

The exhaust valve seal & stem. The rubber seal has extruded around the valve stem. I'm assuming that's not how it should be.

The inlet valve, inner side. I had to push the pump a couple of times to get it to break free.

The inlet valve seal. It also has extruded to fit into the inlet valve hole. Again I'm assuming that's not correct? Both the inlet and exhaust look like the edges are rolled over to retain the seal. I need to do some dissection...

All the valve parts.

The exhaust valve seal really looks bad. Notice the hardened piece pressed into the top of the stem that is contacted by the hammer.

I now have to do the following:
1) clean everything
2) find out whether anything else comes out of th valve assembly.
3) make a lead seal
4) make a new exhaust seal
5) make a new inlet seal.
6) put the whole thing back together and test.


Monday, August 4, 2008

Benjamin 317 Rifle Disassembly, Part 3

So then I chucked a piece of 7/16" diameter tool steel (I have no idea the exact alloy...came from the scrap bin)...

Setting a threading tool on center.

Turning down the OD to 9/32"

First pass threading 32 tpi.

Halfway through.

I swung the compound over to 10 degrees and put a taper on the end of the tap.

Milling the flutes. They have zero rake.

All done.

Milling the flats for the tap wrench.

I hardened and tempered with my acetylene torch and it was done.

Tapping the puller end.

Threads look good.

And I threaded the end onto the valve to check.