Just 'cos I'm interested can you confirm that when assembled minus main spring it does or doesn't cock please?
Dim but willing.
Okay - so you have established that the cocking rod attached to the piston is too short - that's where the problem lies then!
If you say you can get it to work by pushing the piston back by hand, I presume you mean the rod engages correctly with the trigger mechanism - then that must mean that the spring is becoming 'coil bound' before this can happen when assembled - ie, the spring length is too long for the short length of the piston rod.
if so, you have 2 choices.
1. Shorten the spring - which is what I would do - this will allow you to use the existing short piston rod? Taking some coils off to shorten the spring will sacrifice some power, but these rifles were only supposed to produce 10.5 ft/lbs at their optimum anyway and will shoot probably with 8 ft/lbs + okay - remember, you want consistency over power!
or 2. Replace the piston/rod assembly with a second hand one from another rifle - they can be bought on the bay and other places.
I wouldn't be messing with the piston/rod assembly personally - but if you have the time and skills - go for it.
Does this make sense with any of the othe Airsporter 'guru's that know more about this than I do?
If I'm wrong - then just ignore me!
ASM
I am a Man of La Northumberlandia, a true Knight and spend my days on my Quest (my duty nay privilege!) and fighting dragons and unbeatable foe, to right the unrightable wrongs, to bear with unbearable sorrow and dreaming my impossible dreams.
Just 'cos I'm interested can you confirm that when assembled minus main spring it does or doesn't cock please?
Dim but willing.
Sounds like the rod has been shortened, which would indeed increase power. Nothing wrong with that.
But some observations on the geometric affects...
- rear piston skirt would foul end block: this has been addressed by shortening threaded section, but std spring will not work - they will become coilbound.
- cocking slide has to push piston back further: should be OK, but check nothing is fouling - i.e the slide is able to come back far enough and not fouling on the end of it's slot, or anything else. If it is fouling, building up the end of the cocking slot to allow the slide to push it further back woudl work, but don't overdo it, or it will be impacted during firing at the end of the piston's fwd stroke. Or the slot could be extended. Depends what's limiting travel.
To test above I'd assemble the gun with a spare crappy much too short weedy spring and see if it can be cocked, without installing the stock. Look for fouling.
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.
Thank you to all those who responded with suggestions and theories to my problem, sorry for the delay in getting back to everyone.
Ok, assembled the gun minus the spring, will cock ok.
I then removed 5 coils from the old spring and assembled the gun. Now it will not cock as the cocking lever is fouling the trigger guard before the trigger engages.
I then removed another 2 coils, still the same, lever hitting the trigger guard.
I have not tried removing any more coils as when assembling the gun in its present state the piston is under almost no preload, I’m guessing it will be massively underpowered in this state.
Focusing on the piston does anyone know how they are assembled? I know they are brazed together but in what order, has anyone ever seen one before assembly?
I suppose ultimately I will have to obtain a second hand piston and hope it resolves the problem.
Once again thanks for all the interest and useful responses.
Phil.
Forgot to ask in my previous post does anyone have a good picture of the cocking rod through the piston slot at the seal end. I’m trying to establish if the spring seat has also been “built up” to gain more power.
Many thanks
Phil.
Well I finally got round to taking the piston apart. It’s quite a lump of metal to heat up with a pluming torch but the MAP gas did the job.
Here are the links to the pictures if anyone is interested in seeing the component parts of the piston.
http://i513.photobucket.com/albums/t...psqb5gf4pe.jpg
http://i513.photobucket.com/albums/t...pszgu5lvye.jpg
http://i513.photobucket.com/albums/t...psa5pvzj3n.jpg
Interestingly I could not see any evidence of modification? However I assembled the piston with super glue to test my theory, put the gun back together and it cocked first time, no problem.
Just need to assemble the piston and braze it again using my measurements and move on to getting the metal work blued.
Now looking for someone to do the bluing as I have tried a couple of the DIY products and remain unimpressed with the results.
Phil
Glad to hear progress is being made.
I have used Colin Molloy before and his work was outstanding.
ATB
Lee
Hi, I had the exact same issue with my MK3. I`ve had the gun for over 30yrs so i knew it wasn`t a modification issue as its been getting more difficult to cock over the last 5yrs or so until it wouldn`t cock at all. After spending ages with it in pieces i eventually found that the cocking slide pin (the pin that pushes the piston back) was bent back by about 2mm even though its a very short pin. I`ve heated it up and bent it back and now the gun cocks again. :-) I fitted a stronger spring years ago and i guess the extra force and slamming action required to cock it has eventually taken its toll on the pin. Just wondered if yours was also bent back.
i took a photo of the bent pin but i am unable to post images. (maybe its because i`m new to the forum). Anyway hope this helps
Cheers
JG