Saturday, February 21, 2009

Derrick's Short List for the Beeman P17

Part of me wants to run this segment for the P17 first, but I suppose it doesn't really matter.
Please keep in mind that the Beeman P17 has also been sold as the Beeman 2006 and the Marksman 2004. Currently, it goes by the Beeman P17 moniker. Beeman must still be moving through old packaging, as I just saw a gun marked "P17" in a Beeman 2006 clamshell package. They are all essentially the exact same gun and as far as I have been able to ascertain, all the parts are completely interchangeable.

So, if you aren't yet moved to fully disassemble your own P17, here are a few easy tasks that solve most of the gun's annoying little problems. Note: It is unnecessary to remove the entire barrel shroud assembly for the following modifications.

The rear sight screw has a wonderful tendency to back out and cause your point of impact to gradually climb higher and higher. Fun! The simple fix is a slightly longer M4 x .7mm bolt and a corresponding nylock nut.

Nut goes on the inside. I coated the threads of the bolt with a medium strength loctite and allowed it to dry before installation. Care should be exercised when using thread locking products around plastics--like most of this gun. Many plastics don't care for anaerobic thread locking compounds and will be permanently damaged if they come into contact. Be safe and let the compound dry completely on the bolt threads before assembly as a precaution.

Another common problem with the P17 is the tendency for the top cover's rearmost cross pin to wander out of location. That would be the long pin at the far right. A 4-40 tap and a couple 4-40 setscrews will hold it fast. The "latch that looks like a hammer" holds onto this pin when the top cover is closed.

Push the cross pin out with a drift and run the tap through the holes that appear to be made for this exact purpose. Seems like the manufacturer just knew that pin wouldn't stay in place by itself. And it doesn't!

I'm not even sure I needed a tap handle for this. (maybe not even the tap!) The plastic is that soft. While I had the pin out, I also took a couple seconds and polished it--paying attention only to the center latching area.

Started the tiny 4-40 setscrews with a .05" allen wrench, reinstalled the cross pin and GENTLY snugged the screws down.

It's imperative that the setscrews be flush or below flush with the bottom edge.

I did the same procedure with the bottom half of the frame, too. The "hammer that functions only as a latch" also sits on a cross pin. I did NOT remove this pin as I didn't want to fight the latch spring to reinstall. I did start with the tap and ran the setscrews home with the allen wrench. The plastic is actually so soft, I bet I could carefully run the setscrews in without even tapping the frame first. Again, the holes were already molded into the frame. Lucky! And again, the setscrews need to be flush or below.

This small strap, affixed with 2 phillips head screws, holds the barrel in place.

Removing the strap allows the barrel to be slid backward about 1/8" and then straight down and out.

I re-cut the crown on the Taig lathe. It's important to not shorten the muzzle more than a hundredth of an inch or so. This step can be omitted if you don't have access to a lathe.

Next, I polished the breech end of the barrel. This end gets slid across the breech o-ring at the end of the stroke every time the gun is cocked. A smooth surface here will minimize wear on that breech o-ring.

The goal here is simply a nice, smooth finish. Excess metal removal will make the breech effectively too short to reach the o-ring, causing some velocity loss.

This is all we're after.

While the barrel is still out, it's cleaning time. It's unlikely I'll ever remove the barrel again, so the gloves are off. I used J-B Non-Embedding bore cleaner and made a dozen passes. Cleaned it until the patches came clean then finished it off with a good polarizing oil to protect the rifling. Even if you don't want to give the barrel a top notch cleaning, remember to remove the buffing compound from the breech polishing by patching the barrel several times.

I'll get back to the complete overhaul next time.

Friday, February 20, 2009

Derrick's on a Beeman P17 Overhaul, Part 1

Buddy Jason recently sent me his Beeman P17 for the spa treatment. Since I've had quite a few email queries about the P17, I thought a tear down and rebuild illustration guide might be worthwhile. T.W. Chambers & Co. has a great schematic of the Beeman P3 that we can use as a reference point here. Keep in mind that the P17 is a Chinese sanctioned copy of the German Beeman/Weihrauch P3.

Unlatch the pseudo hammer and open the gun as though cocking. With the gun open, use a 2mm allen wrench and loosen the set screw as shown. It's unnecessary to remove the setscrew, just back it out a turn or two so it's no longer bearing against the cross pin. Drift out the cross pin.

Pull the entire piston right out of the compression tube.

This step is completely unnecessary for a routine tear down. I'm going to crown the barrel on this gun as I get further along. I removed one of the small e-clips on the barrel pivot pin and using a drift, pushed the pin out.

Another view. You can see the small e-clip just above and left of the cotton swab.

Using a 2.5mm allen wrench, remove the right side grip panel. Find the seam on the bottom with a fingernail and gently separate. Some of the internal pivot pins may stay attached to inside of the right grip. That's OK. Note their location and pull them out of the grip. Try to not scar them up with pliers.

Using a small pair of needle-nosed pliers, pop the tails of the 2 springs out of the left grip panel to relax the spring tensions.

Pull the pivot pin out until it just clears the mounting hole and remove the sear straight back and out.

Another view. Holding the sear. Pull it straight out.

Unhook the torsion spring from the part that looks like the number 7. Weihrauch refers to this part as the true "hammer".

Remove the hammer's torsion spring.

Unhook the lower end of the coil spring attached to the pivoting lever on the hammer assembly.

Another view.

Next, unhook the top of the coil spring from the pivoting lever . Set the spring aside. Pull the hammer's axis pin out slightly and rotate the hammer assembly as shown on the valve stem and it will lift right out.

Here's the #7 looking hammer assembly. The pivoting piece at the top is the lever. Coil spring shown detached but oriented correctly. Upper loop of the spring fits into the round hole in the lever.

Removing the hammer axis pin shows there's yet ANOTHER spring inside the hammer. Note the orientation of the loop.

I pulled the trigger axis pin and the trigger came right out.
More to come.

Wednesday, February 18, 2009

Resealing the Sheridan Model C

This was a comedy of errors. Basically the Sheridan goes back together in reverse of disassembly, below are notes and comedy that point out a few details.

I used the shim punch to cut concentric seals from lead and rubber.

The inlet valve seal is wrong. I know that now. I cut it way too large in diameter.

You would think I would have caught on...

The exhaust valve spring is tapered, small end towards the rear.

The exhaust valve seal looked clean so I decided to reuse it.

The large rubber washer is also twice as thick as it should be...I thought I had removed the old one but couldn't find it...

At least I got the lead seal right.

The nut is conical to seal against the lead seal.

The face you see when you look down the tube.

Ready to reassemble. I found I had to trim the length of the square section on the wrench to the length of the nut.

That bolt spring...

I placed a feeler gage against it to compress and slid the bolt back in.

Then screwed the locking lug back in. I think it's best if the flats are vertically oriented on the sides so that it smoothly contacts the cam.

The plug goes back in oriented as shown. Then I couldn't screw the valve in...I discovered that the old rubber seal was still in the gun and half as thick as the replacement...preventing me from screwing in the nut (because i now had 3x the thickness) I reused the old one and got it all back together.

Well after getting it back together (in reverse of disassembly) it wouldn't work...still not holding air. So I replaced the inlet valve spring with the one on the left. You can see the old rubber seal above the springs

Still no I turned up a new inlet valve seal from teflon. Look familiar? It worked so well in the Benjamin 317 that I figured why not?

You can see how I didn't make good contact with my replacement rubber seal. Well I'll figure it out next one I reseal...note that I put a stem on the teflon seal on the spring/valve end just as I did on the Benjamin 317. I don't know why I did it instead of just making a disc but it may be stronger this way and resist deforming in the center. I do lose a bit of valve volume this way.

Well the gun shoots about 645-650 fps at 8 pumps with Benji .20 cal cylindrical pellets. So it works! It also held air for several days, which is a good test.

Tuesday, February 17, 2009

Disassembling a Sheridan Model C, Part 2

And on I go...

Cleaned off the worst of the debris with a toothbrush.

This is wrong. I punched out the pin that holds the trigger housing.

Then when I went to punch out the trigger pin the housing just rotated around...

So I held it with a slave pin. Better to first punch out the trigger pin, then the housing pin...

The housing comes out with the hammer spring and guide. Note the trigger spring and trigger spring guide on the right.

The hammer spring and guide looked good.

I loosened one screw on the safety (flat) spring.

Then the other and removed the safety.

The hammer slid out.

Looks just like the Benjamin 317 I resealed.

So I used my handy tool.

And then the valve puller.

The valve connected to the puller.

The valve was dirty but looked ok.

The inlet valve spring was a bit overcompressed, or maybe they're all like that.

The inlet valve seal was definitely bad.

One messed up seal.
Resealing comes up next...