Originally Posted by
Supermick
Thanks to Hsing-ee for the following :-
Tuning The Older Springer
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ALL WORK DONE USING THIS INFORMATION IS AT YOUR OWN RISK - APPLY COMMONSENSE TO YOUR WORK AND SEEK ASSISTANCE FROM A QUALIFIED GUNSMITH IF YOU GET OUT OF YOUR DEPTH. Use a spring compressor and be careful!
If you want your old or new-to-you old spring-piston rifle to give you its best then you could try the following tune-up. It takes a bit of patience and elbow-grease and dosen't involve any drastic modifications but if you follow it carefully your rifle should shoot sweetly afterwards for a good long time.
The following is a basic tune for spring-piston rifles which was common in the late 1970s and early 1980s. The idea is to make the rifle as smooth and consistent as possible, and does not involve modifying the rifle in terms of piston weights, top hats, etc, that is for the more advanced airgunsmith. I used this on a Feinwerkbau Sport recently and it would cut 7mm groups at 25 yards from a rest, and in my 30 year old BSA Meteor which does 10ft/lbs and 20mm groups with a standard spring so it seems to work OK. The guide refers to a rifle with a leather washer, obviously don't soak the washer in silicone oil if it is of a synthetic material, just wipe a small drop of SM50 over it before assembly.
For the full works you will need:
new spring
new piston washer and buffers if fitted
new breech washer
Can of Dri-Slide (or Gun Slide from Chambers) or tube Molykote GN paste
Abbey LT2 molybdenum grease (J.S.Ramsbottoms has this)
Abbey SM50 oil (J.S.Ramsbottoms has this)
Solvol Autosol metal polish ( a car accessories shop like Halfords or a hardware store)
Methylated spirit or white spirit
Very fine abrasive paper
Cheap toothbrush (unused)
18” length of broomhandle
Couple of packets unused ‘J’ cloths or similar
The idea of the tune is to make sure the bearing surfaces are smooth and appropriately lubricated, with the aim of consistent mechanical action giving consistent velocities without dieselling and so giving good accuracy. The molybdenum in the Dri-Slide binds to steel giving a very slippery hard surface.
IT IS ABSOLUTELY ESSENTIAL THAT YOU CLEAN ALL THE PARTS COMPLETELY AFTER POLISHING THEM WITH ABRASIVE PAPER OR METAL POLISH. Use newspaper under the parts as you work and throw them out as they are soiled. Have a clean area to put your clean parts and don’t do ‘dirty’ work next to them. Be careful with naked flames and the hair-drier, the methylated spirit and the carrier element in the Dri-Slide ar e both highly inflammable. WORK IN A WELL VENTILATED ROOM OR WORKSHOP.
1. Place the new piston washer in a pellet tin or similar receptacle and pour over Abbey SM50 to cover it completely. Leave to soak overnight.
2. Disassemble the rifle, taking care to store small parts so they don’t get lost.
3. THE COMPRESSION CHAMBER
A. Degrease all the parts and the inside of the compression chamber using the meths. The broomhandle should have a 3” slot cut in one end so that a stip of J cloth can be slid in and wrapped round to give a cleaning head. Be very thorough, and keep using fresh strips of J-cloth until they start coming out completely clean. Check that the transfer port is clear by using a non-metalisc implement like a cocktail stick and examine carefully by eye. Use the toothbrush and methys to clean the threads that the rear cylinder block screws into. Dry the inside of the compression chamber using further J-cloth strips.
B. If you feel it necessary you can remove the sharp edges on the inside and outside of the cocking-slot. Pack the compression chamber with cloth and using a spatula or table-knife with the fine abrasive paper wrapped around it smooth the inner and out edges of the slot. Don’t overdo this, just remove the sharp EDGES from the slot. Degrease again and be meticulous about removing all the metal filings and abrasive dust using methys and J-cloths. Remove the packing cloth and degrease again until you are sure all the dust has been removed.
C. Using a hair-drier, warm the compression tube by blowing hot air inside and outside the tube body. When it is warm, pour a tablespoon-size amount of Dri-Slide into the compression chamber and roll the chamber around so that the liquid coats all of the surface of the chamber and also further back in the area above the cocking slot. Be careful not to lose all the Drislide out of the transfer port! The chamber can be left to dry for a couple of hours or overnight. Alternatively, rub in some Molykote GN paste onto the whole surface of the inside of the compression chamber.
D. When you are ABSOLUTELY SURE IT IS DRY, use a tightly-wound long piece of J-cloth on the broom handle, burnish the surface of the compression chamber thoroughly. A lot of the Dri-Slide will appear to come off, but it is leaving behind a layer so don't worry.
4. THE PISTON
After disassembling the piston, degrease it inside and out as above, using meths and J cloths. Polish any scratches on the piston body out using the fine abrasive paper, using a rotary action i.e. turning the piston on its axis and holding the paper still so the mark is polished out in a ring around the piston. Polish the whole of the outside of the piston with Solvol Autosol, particularly the back of the piston where it makes metal-to-metal contact with the cylinder wall. Use a J-cloth and to apply and polish off the Solvol. Carefully polish the surface of the bent (part of the piston which engages the sear) with Solvol on a J-cloth drawn tight over something flat and rigid (e.g. a small file). Degrease and clean with meths. Heat the piston up with the hair-drier and coat the inside AND the outside of the piston with Dri-Slide as with the compression chamber, except you don’t need to polish it in afterwards, just leave the coating as it is.
5. THE SPRING
Take a peice of the fine abrasive paper and place it on a very flat surface e.g. a suitably strong piece of glass or steel plate. Polish polish the flat ends on the paper until they are shiny. You can make this a mirror finish if you then polish the ends using Solvol Autosol on cloth stretched over the plate. Degrease and clean the spring carefully afterwards.
6. THE PISTON GUIDE
Degrease inside and out and polish out scratches using a rotary action using the fine abrasive paper and then Solvol Autosol to give a shiney surface. If you like, pad a vice and use a file to remove the sharp edges on the base of the guide. Degrease and clean as above. Make sure you clean the passage through the middle of the guide and get rid of any old grease and dust in there.
ASSEMBLY
1. Take the piston washer that has been soaking in SM50 and squeeze it dry using a J-cloth. Fit it to the piston, avoid getting any lubricant on the screw/bolt attaching it to the piston body. Smear a couple of drops of SM50 around the base of the leather washer (away from its face).
2. Take a lollipop stick and smear a stripe of LT2 grease about 1” in width around the back of the piston (trigger end), be fairly generous.
3. Fit the piston back into the compression chamber, easing the piston head into the chamber gently. It may be a little bit swollen at this point, but persist in easing it in and don’t use hammering or excessive force. Line up the cocking slot in the piston with the one in the compression chamber.
4. Using a small pad of J-cloth, apply a thin smear of LT2 grease to the outside of the spring and a generous layer to one flat end. Fit the spring into the piston with the greased end forwards.
5. Apply a liberal amount of LT2 grease to the outside and INSIDE of the spring guide and fit it to the end of the spring.
6. Smear a little LT2 grease on the threads of the back-block and use this to compress the spring and reassemble.
7. Reassemble the rest of the rifle using LT2 grease on all the main points of wear. Apply SM50 oil to the trigger by dropping it into the mechanism, allow the excess to drip out before reassembly. Replace the breech washer with a new one, and clean the barrel in the normal way. Make sure all the stock screws are tightened appropriately (not too loose, not too tight).
The rifle may be a little bit smokey the first ten or twenty shots but should then settle down to be very consistent. All that is needed in terms of lubrication after this is a drop of two of SM50 at the joints occassionally, and once every 1500 pellets or so a drop of SM50 ***BEHIND*** the piston washer, which can be done by removing the stock and putting the oil in through the cocking slot. Leather washers can take a long time to bed in, so I recommend doing alot of plinking, like two or three tins of pellets, before the gun reaches its peak. Then you should be able to shoot the rifle for thousands of pellets without doing anything more than slip a new spring in occasionally and a sparing use of SM50.
CAUTION: Do NOT over-lubricate. Stick to the amounts indicated here - less is more, especially with polished bearing surfaces.
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