Wednesday, December 22, 2010

Emergency Christmas Repair on a Crosman 38T

Bought a friend a super clean Crosman 38T for Christmas. Actually bought it for him almost eleven months ago. That's some crazy early shopping, but you buy them when they show up. Besides,  he'll be a ten year old kid all over again. Took it home, gassed it up and it worked just fine. Forward eleven months, Kathy and I are ready to wrap. At the last moment, I decide to gas the gun up and give it to him charged. Yeah, you know it. GAHHHH! Almost violated that "do not give non-functional presents" policy. Quick tear down. We've covered 38T (and 38C) guns several times on this tawdry blog. So, I suppose many of these pics are more for my reference to bring me back up to speed on this model. Before gassing up the gun, Fortunately, I'd given the piercing pin a shot of Crosman Pelgun oil before installing the 12 gram CO2 cartridge. Fortunately--because the oil sprayed out at the point of the leak. The oil pinpointed the leak at the seal between the valve and the copper gas tube. Removed everything spring loaded that had potential to shoot across the room. Pulled the cylinder indexing pawl mechanism. just some additional pics The red light indicates the location of said leak. Crosman calls this a "gland seal". Oh kaaay. The "gland seal" at the opposite end was just as bad. A close look at the gas tube showed that it was in pretty poor condition, too. It looked cracked at the valve end. The next morning, a trip to my favorite neighborhood hardware store (remember those?) netted several various pieces of brass and copper tubing. Thanks Carl! Cut and faced a 2.25" section of the 1/8" diam. copper. Started to bell one end with a 30 degree point. Bench block held the tube. A small steel rectangle under the block allowed me to hammer a wider point (60 degree) into the end. Then, a couple strategic taps with the hammer, one end was finished. Cut the bad piece in half. It's the only way to remove the nuts and washer. Installed on the single-flared-end tube. Then repeated the flaring step. Not having any 30 year old Crosman "gland seals" handy, I opted for o-rings. I think that's an #A007 on the left and #A006 on the right. Though there wasn't one there originally, it looks like the valve-end nut is cut for an o-ring at the end of the thread. I added an #A011. It sure won't hurt. Test fitting proved my eyeball method of sizing the copper tube length was a bit shy of the mark. So, I cut the short tube in half, removed the pieces and made another. Why do it once when you can do it repeatedly until it's right? Anyhow, reassembled the gun, gassed it up and it leaked CO2 even faster than the first time. The leak was at the exact same spot. A bit of cursing and a night's sleep later, I replaced that #A006 o-ring with a smaller #A005 then put another one between the small washer and the nut. Like so. Reassembled yet again, shot a couple CO2 cartridges through to test and it's gassed up and ready for gift wrap. Merry Christmas everybody!

Monday, December 20, 2010

Anti-Glare Tube for the Rear Sight

Took some time this afternoon to do some much needed shop work. Put a new grinding wheel on the bench grinder, sharpened most all of my lathe knives, rebored the jaws in the scrolling chuck, verified/realigned the tailstock with pointed indicators... Then I got back to the IZH-61 project.

I wanted to knurl the front of the tube before I reduced the wall thickness too much. Figured I'd better do it now before doing any more drilling--knurling thin tubes is fraught with crushable danger. I impressed a diamond-pattern knurl into the end.

Next up was getting a taper in front of the thread. The taper will act as clearance from the sight base.

Set up the compound on the crosslide and cut at 60 degrees.

With light cuts, aluminum cutting fluid and a sharp knife, I got a halfway decent finish on the taper.

Quick test fit to check those clearances.

Passes, but I noticed that the sight is almost completely out of right windage adjustment and the tube won't install if the sight is buried to the right--there is a small block inside the sight body with a too-small window. The alignment problem is caused by the narrow dovetail on the IZH. Fixing both problems will require disassembly of the sight--I'll get to it in the next blog post.

Back to the tube, it's helpful to remove as much from the center as possible. This prevents the interior from getting into your sight picture. Opened up the base end.

Gave the body a light pass just to clean everything up and get a defined border at the knurl.

Turned it around once again and progressively drilled it to 3/8". Took care to not drill into the taper or I would have drilled it in half.

A small boring bar finishes the hole. Didn't measure, just removed metal until it was thinned out as much as deemed practical.

Another quick test fit.

I'll paint it to match the front anti-glare tube. They don't quite match, so it looks like I'll have to knurl the front tube after all.

Sight tear down and some milling is up next.