B4/5 stripdown guide

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Category: Sample Data-Articles

Published on Saturday, 20 June 2015 14:22

Written by Super User

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Hi, a basic SDG, have fun its easy.



Remove screws from front of stock



remove the screw from the rear of the trigger guard and separate the stock from barrel



undo the screw holding the under leaver arm to barrel, unclip leaver from the retaining clip and lift out from the piston/spring guide







next is the anti bear trap. easy only one screw. DONT LOSE THE SPRINGS





remove the spring and spring guide, you can use a spring compressor system or simply put a socket on the floor, place the rifle over the socket, barrel pointing towards the ceiling, push down on to the socket realising pressuer on the retaining pin. get a friend or partner to push out the pin (theres not a lot of pressuer) lift up the barrel and remove the spring.



now to take out the trigger. remove the circlip from the sear pin and pull out the pin. the rest of the pins will just push out.



pullout the trigger, it will need a tug due to the burrs on the inside of the trigger housing



now the piston and piston cylinder will drop out



The DB4's trigger is generaly regarded as being a bit stiff. I'v spent quite some time working out what solutions i can come up with? it's detailed here.

Click to see full size image

Make sure the gun is unloaded and not cocked before working on it!!
The trigger is easy to strip down, only 3 pins need to be removed. The first one to be pushed out is the small rearward one, it holds the trigger spring in place. Next one is the small one that goes through the trigger blade. Finally the large one is removed (this one holds the sear) after the anti-bear trap springs have been un-hooked.



If you look at the end on picture u'll notice that the spring rubs on the rear of the blade and is responsable for much of the "feel" of the trigger!! U'll notice that it is a rough casting and needs to be improved.




The areas highlighted in red need to be polished to a high shine without changing any of the shapes or removing to much metal. There is one exeption, the rear of the blade where the spring rubs, the casting is so rough some filing may be required first!! As i said it is what gives the trigger it's feel so must be smooth!! (Note the spring in the piture is upside down   )


Polish highlighted areas



Like this

and this

After polishing the tigger can be greased with moly grease on the sears (newly polished areas) and re-assembled in the reverse of the strip down!! The spring will take a bit of coaxing to get back in but the rest is easy!! The polished area that the spring slides on will also need to be greased

Trigger unit  greased, assembled and ready for use!!
Hope this guide helps!

This is a guide how to do a simple tune on a springer. Not how to disassemble or assemble it. You will have to follow the appropriate  strip down guides for the model you have. It also doesn't include bought in tuning kits with a new spring, Delrin power bands and top hat/spring guides.
The cost here is minimal and effective. A few different grades of wet-n-dry sheets, some thick dowelling or whatever you can find to hand, a couple of metal washers, a small sheet of plastic (empty fizz/cider bottle), or thin tin sheet, a tube of metal polish and a bit of card. Possibly a blowtorch (I have even used the pilot light on a Superser portable gas stove), and angle or bench grinder may be needed.

When using the spring that came new in the rifle/pistol, you will probably need to  polish/smooth the spring coils. So find something such as length of dowel rod that will fit inside the spring but small enough to wrap some wet-n-dry round it. Fix this on the end that doesn't go inside the spring with whatever sticky tape you have to hand. If you drill a small hole in one end of the dowel, then screw in a long shanked screw to where the thread stops. Cut the head off with a hacksaw. The shank can now be fitted in a drill chuck. These are known as sanding flags. You can also make them like in Porky's link
http://ukchineseairgunforum.myfreeforum.org/about22909.html
Run this up and down inside the coils a few times. Now wrap something else round the dowel so it's a tight fit in the spring. You can now spin the spring in the drill while holding a sheet of wet-n-dry on the outside.
If the ends are flat, these will need to be smoothed and polished. Hold the spring upright and rub the end in a circular motion on a sheet of 400 wet-n-dry, then 600/800 on a flat surface. Once the end is fairly smooth, use a small amount of Solvol Autosolve or similar metal polishing paste on the none picture side of a cereal packet. Use the same circular motion on this. This will bring up a mirror finish to the ends. Then remove all traces of polish.

If one or both ends are not flat, but have been cut mid coil, the end/s will need to be heated with a blow torch until red and the end coil collapsing (squeezed) together. I've always done mine with a pair of pliers, others say push down on a flat surface. Do not quench the end, but let it air cool, otherwise it will become brittle. Now grind the end flat and follow the above for finishing.

The cylinder will need de-burring as there are normally rough machined edges on the in/outside of slots and screw holes. If there are really rough edges, these will need to be taken down with a small metal file first. Then use a thicker dowel sanding flag to smooth further. Finally run a courser flag in and out of the cylinder slowly to minutely scratch it. Try to aim for a diamond shaped pattern. This will help hold grease on the cylinder wall.
Now do the same to the piston without the final course flag. If there are any angles in the slot where the sear engages on the piston. Do not alter this angle. It is designed to engage with the sear.  Doing so may make the trigger unpredictable and dangerous.
The   internal spring guides vary from model to model. Some are in the piston some are fixed to the end caps, some have both. If made with metal these can be polished to a shine. If plastic there is little that can be done. Just make sure that there are no rough edges where they have been cut from the mold.
Wash and brush all the gunge and swarf away with isopropenol alcohol. If you can't get it, white spirit will do. You don't need little bits of metal left in the cylinder.

Polish two metal washers. One  that will fit inside the piston and one that will go over the rear spring guide. These are polished the same way as the spring ends. Make sure the washer drops all the way to the bottom (piston seal end), because those that have a spring guide in the centre of the piston, sometimes have a slightly larger base than the guides diameter itself and the spring must go in it's full length to the bottom.
When a spring is released it rotates. The polished washers allow this to happen much easier. This then helps with less recoil being felt.

Now make a piston liner as per this link
http://ukchineseairgunforum.myfreeforum.org/about37249.html
This will stop a lot of the twang from the spring and also helps to hold the grease in the right place.

Grease the spring with Moly paste. A large tub that will last a lifetime can be obtained from Halfords or any motor factors. It's the stuff used for CV joints. Don't slap it on in big dollops, but use sparingly as it's well sticky. Also grease the washers and the spring guide as these are all metal to metal contact.

Insert the piston liner followed by one washer. Now the spring and top washer and reassemble.
These things are all done to reduce friction on the moving parts. This should now give a much smoother and quieter action.
The cost is very little except for your own time. This is not knocking professionally made kits that will enhance most airguns even more, but a cheap method to hold down the costs.

I filed, sanded and polished either side of the trigger housing and polished these bit:



To put the trigger back in I put the large sear pin in first, then the little pin through the top of the trigger, and then reach up inside the gun and push the bit of the trigger that sticks up down flush and push the other pin through while holding it down. Then push the bear-trap pins in.

This worked first time for me.

The only other thing I can think of is.... did you put a plastic spring liner in? If you did, did you cut out a slot to match the slot that the sear pin sits in?

I'm very new to all this so I may have got some terminology wrong - or be talking complete b*llocks (as is often the case!)