Another BSF S20 WCM Tear Down Part 2 Final

Finishing up the S20 today.

Glossing over most of the steps since this is the second time around for this model on the blog. I cleaned all the sticky crud out of the compression tube and all the various components. Polished the back end of the piston body, cocking rod notch, sear...

Once it was clean, I soaked the leather piston seal in oil then gave the internal parts a thin coat of Buzzy's Slick Honey.

Piston rod is brass brazed into the body.

The brass was covered with verdigris when first removed.

With the piston in the tube, trying to reinstall the barrel/breech block to the compression tube took some patience. The forks on the tube are extremely tight to the breech. The cocking lever also needs to be reinstalled through the trigger block and into the slot.

Used a dental pick to lift the trigger spring out of the way while seating the cocking lever. Once the spring was out of the way, the lever was positioned then the breech was installed into the forks. A transfer punch was used as a slave pin for the barrel pivot.

Was having trouble getting the peined rivet aligned with the far side of the trigger block. It kept moving off center as it was binding on the cocking lever. With a chainsaw file, I added a small radius into the cocking lever for pin clearance. Exact location not critical as the barrel can be broken open to align the groove with the pin. The red vinyl tape on the slave pin prevents it from falling out.

Click any image to enlarge for more detail. I shielded the gun with foil to prevent getting metal filings into the action. Sorry, I didn't show that in the pics.

Barrel opened to align the groove with the pin.

Pin tapped home and barrel pivot pin installed. Yes, glossing.

The rest of the reassembly was uneventful. Spring installed...

Added a thin rotation washer to the base of the spring guide.

Remember that there are two cross pins for the sleeve/spacer/endcap whatever you want to call it. Pinned the rearmost hole first (without the rear sight assembly) to restrain the mainspring. This allowed for much easier installation of the sear on the forward pin as I was no longer fighting the mainspring while attempting to align the cross holes in the tube, sleeve and sear--then pin it all together.

Removed the rear pin after seating the sear and sear spring. The forward pin is now retaining the mainspring. Installed the rear sight block and it was pretty much a done deal. Finished the gun by installing the grip.

Another BSF S20 WCM Tear Down Part 1

Apologies, as Nick has already covered a BSF S20 overhaul in fine detail several months ago. Mine feels as though the mainspring is covered in cold molasses and obviously needs some attention, too. I'll be brief, as I don't have much to add--at least in part one. I believe I did a bit less disassembly than he did and it certainly went easier.

A pic of the BSF S20 by itself doesn't give scale for it's true size. A Crosman 2240 provides some perspective.

The WCM model has thumb rests on the stock. It's not really just a grip when it uses this much lumber.

Started the same as Nick did before taking a couple small departures.

First removed the rearmost pin and set the rear sight assembly aside.

The second pin holds the sear and end tube. The drift is now retaining the mainspring.

Another view.

Sear, spring and small spring guide.

Compressed the end tube slightly against the bench and pulled out the drift. Slowly released the mainspring and guide.

The grease on the mainspring has hardened and has the consistency of roofing tar.

Piston is full of the tar, too. Can't get the piston out without removing the cocking lever first.

The breech pivot is a pin rather than a shoulder bolt.



Knocked the pivot pin out and found that it also retained the plunger and spring. Actually, the plunger fired across the bench. Clever design. Most guns use a separate pin to hold the plunger/spring in the breech block.

Nick's posts made several mentions of the aggravation he had while dealing with the peined pins on the trigger block. There's three of them, but only the front pin holding the cocking lever against the compression tube has to be removed to extract the piston. Took care to not damage the leg of the trigger spring. Didn't knock the pin all the way out.

With the pin removed, the lever was wiggled from the cocking slot then the piston body was pulled free.

The leather seal is in dandy shape despite being covered in sticky glue.

More soon.