I think the BSA Mercury is a beautiful looking air rifle with the way the trigger block curves down from the back of the piston cylinder to meet the wooden stock, The chequering on the pistol grip, The short cocking linkage slot in the fore stock, and the slightly raised cheek piece. That's why i thought it would be a good idea to get her back to her former glory, so with a Titan XS main spring, piston washer seal, and a breech seal from J Knibbs i was on my way.
This air rifle was given to me with a severe bend in the barrel at the breech block where it had obviously been fired with the barrel left open though this was an easy fix with a vice and a metal tube, and the forks that held the breech were very loose which again was fixed with the use of the vice. Also some one had put a spring from an SMK B2 in it and the breech seal was worn, which is what shall be adressed in this blog
|BSA Mercury ready for working upon.|
I removed the stock by removing the two cross head screws on the fore stock then the long flat head bolt at the bottom of the pistol grip, this is recessed into the grip and runs diagonally through the grip and screws into the trigger block.
|Stock removed, note the long bolt that that goes through pistol grip.|
|The hole in the trigger unit above and in front of the trigger guard is for using an iron bar for leverage|
Then the cylinder, breech, and barrel were taped into the spring compressor to have the cocking linkage, spring, spring guide, and piston removed in a tidier enviroment than the work shed, basically the dining table in the kitchen
|The spongy two inches of preload of the old spring.|
The cocking arm linkage is articulated and once the cocking linkage guide and screw pin that connects it to the breech were removed, could now be removed and the piston could be slipped out the compression cylinder. The guide is held on to the cylinder by two cross head screws and holds a plate in place against the cylinder for the cocking linkage to slide against, it also has two tabs that fork out either side at 90 degrees for the fore stock screws. Where it connects to the breech there is a spacer washer that keeps the two walls of the linkage firm and tight, this is an easy one to loose if your not careful so i kept a watchful eye and it fell into my hand as i removed this end.
|Old crumbling washer on the piston.|
|Piston head and body cleaned and polished showing the holes for the pin|
|Making the replacement washer|
|The new shiny smooth O ring seal below with the old tired one above.|
The replacement O ring seal slipped into place on the piston head easily, comparing the old and new one showed me the original was worn and had streached with time and use.
I removed the compression cylinder and filed away any sharp edges, then went through the same cleaning and polishing routine i used on the piston. Though this time all the materials were clipped on to a slit in the end of some 6mm aluminium tube and wrapped around the end so i could get right down to the transfer port, looking at this made me think it quite a small diameter for a .22. The whole of the inside of the cylinder was shining bright when i had finished as i spent much more time and effort doing this part, it was then taped back in place on the spring compressor with some blocks at the breech support to bring the end of the cylinder over the end of the compression tube bed.
|The preload of the Titan XS spring, all 34 coils of it. In the fore ground is the old SMK spring.|
The new Titan XS spring has 34 coils where as the the old SMK spring has 31 coils and was compressed a fair bit, this presented me with over four/five inches of preload which would surely test my DIY spring compressor. Also the curved shape of the trigger block meant that the end was off center for the threaded bar on the compressor, this was sorted by building a housing from two pieces of wood and some metal sheet. With the trigger block in this jig i could compress the spring while presenting the trigger block to the cylinder at the correct place and angle, once presented half a turn once the threads started to bite would hold the trigger block to the compression cylinder. Giving me time to remove it from the spring compressor and screw it into place with the use of the iron bar, though the last bit would need for it to go back in the vice and finish off screwing it together.
|Trigger block in it's jig and compression tube just hanging over it's bed. I had to compress the spring by hand a bit so it would fit in the spring compressor.|
Applied Abbey SM50 to the O ring seal and some Abbey LT2 grease to the last inch of the piston,then this was slid into the compression cylinder. Followed by the spring with both the ends polished, i had dabbed LT 2 grease over the front half of the spring then taking a cloth i spread it thin and evenly by wiping down and around the whole length of the coils, then LT2 grease was applied to the ends or the spring and the outside of the spring guide and both washers. The jig supporting the trigger block was lined up and placed behind the rear washer with the threaded screw bar of the compressor directly on the back of the metal sheet at the back of the jig, this would allow me to turn the trigger unit 180 degrees when the spring was compressed enough so the threads would bite.
It took a couple off attempts to get it right in the end, and the spring compressor held together with the force of all the preload though i could see the poor thing staining. Once it was together the articulated cocking linkage was greased at the hinge, at the breech block on the screw pin and spacer washer, and on the tabs that go into the cocking slot and moves the piston so it cocks. The metal plate was slipped under the cocking linkage and the guide screwed back onto the cylinder, and then the stock was screwed back on leaving only the breech seal to be replaced.
When i cocked the gun i could straight away feel the extra effort needed for the new Titan spring but it was still easy effort, linkage and internals moved smoothly and made no noise. Putting a Wasp No 2 pellet into the breech i locked it back an took a shot, there was no twist or kick to speak of as the piston slammed home which was a definate improvement. I will have to knock up a slip washer and top hat in the fonley lathe when i get some delrin bar, but for now its just a matter of prising out the old breech seal and pressing the new one home.
I did have a lot more pictures for this blog but before i had chance to move them over the computer stopped working, so it had to be re booted and anything put on since it was last saved two weeks before was lost. But some were moved over to the blog before this happened so it wasn't a total loss, any way i'm sure i'll be coming back to the Mercury some time in the future so i'll get some better pictures then.
Wing Commander Sir Nigel Tetlington-Smythe.