Introduction: Vintage BSA Scorpion Pistol_ Strip Down Guide.
The BSA Scorpion is a monster of an airgun pistol; in the 70's and 80's it was the most powerful around.
You may consider this a niche Instructable.
http://en.wikipedia.org/wiki/BSA_Scorpion_Air_Pistol
I bought a secondhand one in a private sale online.
I had never seen one in real life but I was fascinated by what I had read; when it arrived I laughed out loud; it's massive.
The reviews praise it's power and accuracy. (for targets only, not for vermin control).
I could not find a pictorial strip down guide anywhere on the internet, so here is my own.
Any improvements corrections or tips are welcome.
The exploded diagram is from the Chamber air gun spares site.{ I have modified it a little).
They supply a good range of spares for vintage air guns.
http://www.gunspares.co.uk/shopdisplayproducts.asp?page=1&id=24706&Search=
Step 1: Tools.
You will need:
Tools
A small flat head screwdriver.
A Posidrive screwdriver.
A 3mm Allen key.
A slotted tube ( using a bicycle seat-post; this will be explained in the guide )
An improvised spring compressor ( using a sash-clamp; this will be explained in the guide )
A wooden dowel.
Parallel punches ( you could get away with it without them)
Materials
Molygrease
Oil.
A breach seal ( if needed )
A buffer washer ( if needed )
A piston seal ( if needed )
Step 2: Removing the Grip.
Firstly unscrew the bolt holding on the safety catch and remove the catch.
---------------------------------------------------
There is catch on the heel of the grip
Very carefully push a small screwdriver into the opening.
Study the photos; the aim is not to lever open the catch but to release the little arm that holds the catch on.
Once removed you can see how unusually delicate this component is for such a hefty beast.
------------------------------------------------------------------------------
Inside you will see the head of an allen bolt.
Undo this.
At the rear underside of the pistol is a silver posidrive screw; undo this.
-----------------------------------------------------------------------------
Carefully pull the grip away.
It is much lighter than I thought; not solid plastic.
Step 3: Remove the Sights.
The front sight is held on by a single screw;undo this and remove the sight.
----------------------------------------------
The rear sights held on by a single screw and a small peg; undo the screw and remove the sight.
Step 4: Remove the Barrel Pivot.
The barrel is held on by a roll bar; called the barrel axix pin; this is simply a tube with a split along its length.
These bars have small plastic plugs over them; carefully remove by levering out with a small blade.
I placed the cylinder over a block of wood with a hole under the axis pin.
Using a parallel punch I gently tapped it through.
Step 5: Removing the Trigger Assembly and Barrel.
Remove the two silver trigger plate screws on each side of the trigger assembly.
-------------------------------------------------------------------------------------------------
Gently pull it away from the cylinder being aware of the long sear which is under a small amount of tension.
-------------------------------------------------------------------------------------------------
The barrel and attached parts can now be separated from the trigger housing by sliding the cocking lever out of the trigger plate.
-------------------------------------------------------------------------------------------------
A quick inspection shows that the plastic on my trigger has a crack in it but I don't think that this affects performance.
Step 6: Making a Spring Compressor.
There are countless ways to do this ranging from using the jaws of a workmate, a car jack, sash clamp etc.
I used a sash clamp as it seems the easiest and safest.
http://www.woodworkforums.com/f152/clamp-not-cramp-9180/
-----------------------------------------------------------------------------------------------------------
Firstly though you have to make a tool to relieve the compression on the mainspring retainer. . . I'll call this ' the reliever.'
This is simply a tube that fits into the back of the cylinder and the prongs sit either side of the mainspring retainer (which essentially is just a large pin) ;
A tube with a roughly one inch diameter is what you want; I used an old seat-post from a bike; it took about 1 minute to make with 3 cuts on each side with a hacksaw.
----------------------------------------------------------------------------------------------------
As you can see in the photo, I laid the sash clamp down (with some wooden blocks to protect the cylinder jaws.) and held everything down with bungees.
I inserted the reliever into the cylinder as described and gently tightened the clamp, not much just enough to take the spring pressure of the retainer.
Step 7: Removing the Retainer.
OK, gently tighten the clamp to relieve the pressure on the retainer; just a tiny bit; then tap the retainer out with a parallel punch.
It came out very easily; I could have probably used a wooden dowel.
Step 8: Removing the Mainspring.
With the retainer removed I began to undo the sash clamp.
It only took a couple of turns and it was fully de-compressed.
Pull out the spring and the spring guide.
Step 9: Removing the Mainspring.
I had to use a wooden dowel to remove the piston.
I had to shape it to do the job.
It was not bad at all.
The buffer washer and piston ring are in good condition.
( The buffer washer can disintegrate and if not replaced in time seize the piston making it very, very hard to remove. )
Step 10: Possibly Replacing the Buffer Washer.
The piston head is held on by a type of circlip.
It is hidden under a washer.
Remove this washer easily by carefully levering it up and then inverting the piston so that it falls away.
The split washer can then be seen.
The washer can be opened up with two small screwdrivers,
This is fiddly and as my buffer washer is in good condition I do not need to do this.
Step 11: Cleaning and Re-greasing.
Clean everything and replace any parts that you need to.
Put moly grease behind the piston ring, all over the buffer washer.
My mainspring is showing signs of wear on the ends; I put grease on the ends ( There is a type of spring-tar that some people use on the whole spring to reduce the twang ; I am not using this.)
I put grease on the spring guide also.
Step 12: Re-assembly- Mainspring.
Push the piston back in with the dowel.
Replace the mainspring and spring guide.
It is the same set up as before, with the clamp and seat post.
I found that I had to make a slightly deeper cut in the reliever; this was because the spring gude's two parts were separating.
Ok tighten up the clamp to allow the retainer pin in.
This just slides in; no hammer necessary.
Release the clamp slowly.
Step 13: Plunger.
While I'm here I should check the barrel latch
Put the barrel in the sash clamp to isolate the roll bar.
Tap out the roll bar and inspect; everything. re-grease and re-assemble using the clamp.
Step 14: Re-assembly- Trigger.
I pulled the long sear down with some hairy string and secured it there with an ikea pencil.
I slid the cocking lever into position in between the trigger housing and put the whole assembly into place.
This is how it looked until through the assembly hole, with the long sear resting on the intermediate sear.
I replaced the grip and safety lever.
After cocking I needed to move the safety lever up and down once to re-sit everything.
It is now very smooth to cock.
Happy Plinking.
FOH
