improved model B

[edbear2]

gentlemen, in my youth there was an American television series called 'the twilight zone'. I don't think they ever made an episode about an air rifle but they could easily have used mine. i'am now in a position to state a few 'facts'.

01 if you remove the springs the rifle will cock with a crisp click as the sears engage. it does this every time.

02 if you replace the springs it will not cock although the trigger is pushed back to a position which must be very very close
to the cocking position.

03 following edbears very clear instructions the space between the rear of the piston and the face of the trigger block is
3.46mm measured with a digital Vernier gauge. the available depth in the piston to accommodate the spring is 95.42mm.
3.46 + 95.42 = 98.88mm. lets call it 99mm.

04 there are two springs each with 20 coils. the average coil measures 2.25mm. 40 x 2.25 = 90mm which means that there
is 9mm of 'free space' before the coils would bind on compressing.

I think arbe's suggestion is a good one as it doesn't involve any cutting or filing of the existing metal but I havn't tried it yet.
supposing it works it still doesn't explain why it cocks without the springs but not with. i'd really like a proper engineering explanation before I start chopping things about or should I accept that the world of antique airguns is full of mystique and unexplained things ?

HMMM...If the trigger is moving back with the springs in it sound very close, so it may be the loading of the springs taking up some slack against it cocking with no springs, can you rattle the cocking arms, ie. pivot wear?....Also are the springs a tight fit in the piston when not compressed as if so the front one may not be fully compressing so the coild height measurement will be in effect false.

ATB, Ed

[j_potter]

hi micky, I now lay awake all night thinking about this problem and yes I came to this conclusion last night. rather than experimenting with what may possibly be original springs, does anyone know of a spring I can buy which they know fits. I can then chop this about if necessairy.
many thanks to everyone for all these replies. I feel i'am edging closer to an answer !

[j_potter]

sorry ed I missed your post earlier. the springs are a loose fit in the piston. there is a tiny amount of play in the cocking arm joint but that would be taken up when it pushes the piston without the springs and in that condition it cocks fine. I think i'am now getting into the place where I try things even though they seem illogical but I don't find that very satisfactory. I think it was keith joseph who once said " I can see that it works in practice, but does it work in theory ?"

[Binners]

Ah well J P, just look at the hours of pleasure and experience this old rifle has given you Lucky man

[edbear2]

Two things I forgot, does the breech block have a thinwall tube extending from it (piston rod guide) and is the piston rod itself rock solid in the piston?

Otherwise I am baffled if your spring calculations are correct

ATB, Ed

[j_potter]

hi ed, yes it does have the piston tube and the piston rod is a nice sliding fit inside it. indeed, you can slide just the piston up to the trigger block and it latches just fine. and yes binners, you're quite right. I have had hours of pleasure taking this apart and understanding it's mechanism. I just wish I could also shoot the b****y thing !

[j_potter]

hi ed, I've just had a thought prompted by your last reply. the rifle's now re-assembled so before I strip it again do you know if the piston rod screws into the piston ? it looks like it does on the cutaway diagram danny sent me. if so, do you think I could loosen the screw holding the washer and unscrew the rod through one complete turn ? this would have the effect of making it a tad longer and then I think it would work.

[edbear2]

hi ed, I've just had a thought prompted by your last reply. the rifle's now re-assembled so before I strip it again do you know if the piston rod screws into the piston ? it looks like it does on the cutaway diagram danny sent me. if so, do you think I could loosen the screw holding the washer and unscrew the rod through one complete turn ? this would have the effect of making it a tad longer and then I think it would work.

Hi, the rod is a screw fit, but has a shoulder and once tight is machined and a keeper screw inserted to stop it coming adrift, the keeper is visable when you remove the washer....I would advise against undoing as will become unstable.

ATB, Ed

[micky2]

hi micky, I now lay awake all night thinking about this problem and yes I came to this conclusion last night. rather than experimenting with what may possibly be original springs, does anyone know of a spring I can buy which they know fits. I can then chop this about if necessairy.
many thanks to everyone for all these replies. I feel i'am edging closer to an answer !

Hi JP. sorry but l don't know what new spring would fit as a replacement, but someone on here might be able to help you on that. l still think it is the spring that is the problem as you say that the piston rod is nice and tight, which as Ed as said that would be another cause.
ATB,
Mick.

[Binners]

I bet some kind chap on here will post you a spring to try, they are the same as Imp mod D, I'll wager. I don't have any in my sulking shed at the moment

[j_potter]

hi guys, no need for a spring IT WORKS !!!!!!!!! Following arbe's suggestion I put a small strip of plastic 0.9mm thick ( a slice of credit card, (well who needs that any more ) between the cocking arm end and the piston. it now cocks fine. I think i'll ask an engineer friend to put a dollop of weld onto the end of the arm which I can then file back into shape.

I'am really gratefull and moved by the help and encouragement of everyone on here. The price of the rifle has been amply repaid by the realisation that the world is not quite as cold and heartless as the media seems determined to portray it.

best wishes and thanks to all

joe

[micky2]

hi guys, no need for a spring IT WORKS !!!!!!!!! Following arbe's suggestion I put a small strip of plastic 0.9mm thick ( a slice of credit card, (well who needs that any more ) between the cocking arm end and the piston. it now cocks fine. I think i'll ask an engineer friend to put a dollop of weld onto the end of the arm which I can then file back into shape.

I'am really gratefull and moved by the help and encouragement of everyone on here. The price of the rifle has been amply repaid by the realisation that the world is not quite as cold and heartless as the media seems determined to portray it.

best wishes and thanks to all

joe

Hi Joe, glad you have got it working again and you can now enjoy it, good tip that and it has saved you some hassle.
Mick.

[frogboy]

Congratulations, glad to hear it's now performing

ATB

Lee