I've just completed a refurbishment of my Original Model 35 air rifle. This was bought for me back in 1977 so its 41 years old and has sat unused for 35 years. I'd read so much about how difficult they were to put back together, because of the ball bearing trigger mechanism, that I have never attempted to take it apart before but armed with information from this site and others I thought I would give it a go. I used a sash clamp as a spring compressor but next time I will build something to hold the rifle and the sash clamp in place as it did have a tendency to try to move sideways under pressure.
The main spring was broken in two places and I decided to go for the full TW Chambers ultra tune kit with the Titan OS1 spring. This comprises a delrin spring guide and top washer to allow the spring to rotate freely, a new leather washer, the Titan spring and moly grease and and lube to soak the leather washer. After a good clean of decades of gunk with carb cleaner I reassembled with the new parts. The main difficulty getting it back together is the amount of main spring preload also the trigger itself is awkward to fit as you have to compress the trigger spring to get the pin in and it is an awkward shape to clamp, I ended up running several turns of string around the trigger and rifle to tighten it up. The ball bearing trigger unit is not an issue if you put a dab of grease on each of the ball bearings to hold them in place before you slide it into place.
I wasn't happy shooting it with the leather washer in, it was inconsistent and producing a lot of smoke and shooting at under 9 ftlbs. It maybe needed more time to run in or I maybe hadn't soaked it long enough but when I came across Vortek synthetic seals I ordered one from Tony Burton. I also measured the trigger spring and ordered a coupled of alternatives of similar length but lower diameter wire, to give a softer trigger pull.
A couple of other issues I had to deal with were a split in the stock across the piston grip and also try to improve the scope rail as scopes have a tendency to slide backwards on it. I glued and screwed the stock together (one screw up from the bottom of the pistol grip and a longer screw in the back of the trigger guard) and drilled a 4mm dia hole in the scope rail. The stock is now solid and the scope does not slip anymore.
With the leather washer replaced and a weaker spring in the trigger it's shooting as nicely as I can remember, at around 9.5 ftlbs with Bisley LRG pellets. It was always a very accurate air rifle and today I got a 5 shot group at 40 yards that I can cover with a 1p piece so I'm very pleased with how it's turned out.