Friday, 12 April 2013

Stripping the Diana/Original Mod 16

The Mod 16 is the small one above the BSA Mercury.

This is an old smooth bore junior air rifle, and it only shot a pellet two inches down the barrel when i first got it. Letting some synthetic oil soak into the large leather breach seal and piston seal and letting it soak for a day got it firing, inch groups at ten yards on average. Still not owning a chronograph i could still tell it was well short of its full power, so why not strip it and see what could or needed to be done to improve on this.

Checking out Chambers exploded chart and spares list i could see that a lot of parts were obsolete, but my bodging skills are improving nowadays. To take the stock off two flathead screws on the fore stock and one screw which held stock, trigger, and housing were removed. 

One of the two front stock screws

The rear screw is one long screw that screws into a circular bolt with a flathead driver fitting, the trick with this was to take an old flathead screwdriver and grind the middle out leaving two flatheads spaced far enough apart to grip the round bolt leaving the long screw to undo freely. Out came trigger, trigger spring that rests in a hole in the stock, and spring cylinder and barrel.

The rear stock bolt/screw that holds a lot of stuff together.

I pulled the tight fitting metal end cap off and and the spring guide retaining pin fell out, as the metal spring guide had two tabs that twisted into small slots at the back of the spring cylinder. The spring was worn so pushing the back of a screwdriver into the end of spring guide and giving it a twist i slipped the tabs out and out came spring guide, spring, and piston.

Using a rod i  wrapped some wet and dry dipped in white spirits and thoroughly cleaned the inside of the cylinder, then removed all residue with kitchen towel. Using the same method i polished it with OOOO wire wool and cleaned it again with kitchen towel, then finally gave it a really good polish with Autosol metal polish making sure to clean it out a good four or five times. This method was repeated with the piston and the spring was given a good clean with white spirit and a kitchen towel and each end polished, i slightly roughened the leather piston seal with wet and dry and let some Abbey SM50 soak in for a few hours.

Adding some more Abbey SM50 to the side of the piston seal and Abbey LT2 grease to the last inch of the piston i carefully slipped it into the cylinder, two metal washers either side of small rubber sink washer lightly smeared in LT2 grease were placed in ahead of the spring also lightly coated in LT2 grease. Spring guide also greased was pushed back in with the back of a screw driver and the tabs locked into their slots, then the pin was replaced and the end cap tapped back on with a mallet.

It took a couple of attempts to line up stock, trigger and spring, and the cylinder body together and slip the screw through but it was no biggy, the rifle actually dents wood with Hobby's instead of slightly marking it now. 

See the trigger tension spring behind the trigger?

I can't really justify spending much money on the Mod 16 just yet, the price of a replacement spring for this rifle is the same as one for the BSA Mercury and that is a wicked air rifle. But it was fun doing it and its got a little more poke to it now, and hopefully should do better groupings at ten meters now its had a clean and relube.


Wing Commander Sir Nigel Tetlington-Smythe  


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