BSA Light Pattern spring replacement  

 
mrben0
(@mrben0)
Member Registered

Looking for some advice, i have ordered a new spring for one of my guns from John Knibbs, i have checked and apparently it is the correct one but when fitted the spring will be solid once cocked, is this correct? also how do you guys fit these new springs, the old ones are easy you can do it by hand, but the new one forget it it will need a spring compressor.  I usually use a large sash cramp for this job but due to the shape of the gun this is not simple.  any help would be much appreciated.

Edited: 4 months  ago
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Posted : 20th January 2018 15:27
Garvin
(@garvin)
Owner Admin

You may have to cut a coil or two off the spring. Make sure you flatten the cut end with a Dremel or something. You shouldnt have to force the spring in these old BSAs and if it's coil-bound it won't cock anyway.

If the spring sticks out only a couple of centimetres or so, and the trigger block screws on with just your weight on the butt, it should be about right. I've found in the past that velocity was higher in a Light with a softer spring than a stiff one.

Edited: 4 months  ago
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Posted : 20th January 2018 17:05 mrben0 liked
mrben0
(@mrben0)
Member Registered

Many thanks, what velocity should I expect, currently running around 420 fps with 4.52 JSB's?

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Posted : 20th January 2018 17:48
Garvin
(@garvin)
Owner Admin

Sounds a bit low, but running in the rifle will see velocities rise if you replaced the piston washer.

See here:

https://forum.vintageairgunsgallery.com/vintage-bsa-resources/vintage-bsa-lincoln-jeffries-technical-tips-faqs-2/#post-514

and here:

https://forum.vintageairgunsgallery.com/vintage-bsa-resources/vintage-bsa-lincoln-jeffries-technical-tips-faqs-2/#post-515

Edited: 4 months  ago
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Posted : 20th January 2018 18:36 mrben0 liked
mrben0
(@mrben0)
Member Registered

Just a quick update, I resized the new piston seal, not quite as loose as Lakey's recommendation but close, it slides down the bore with ease.  I also shortened the new spring from John Knibbs as per your recommendation to give 20mm pre-load the gun could easily be assembled by hand, shoots pretty nice and is now delivering velocities of 555 fps +/-5fps over a 50 shot string.  first shots were all over the place I think it was dieseling on the oil in the piston seal as i had readings of 728fps followed by 690 fps then 470 it then stabilised at 555 fps as previously mentioned.

Thanks for your help guys, much appreciated, this is a great site, keep up the good work.

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Posted : 21st January 2018 08:54
Garvin
(@garvin)
Owner Admin

Nice work! It should settle down with use and the power will go up. ? 

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Posted : 21st January 2018 12:03
evert
(@evert)
Member Registered

Do you have any measurements of the replacement spring?

I am currently working on my own Light Pattern BSA, and have fit a cut down Chinese under lever type spring. Just wondering If I should cut it down a bit more.

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Posted : 28th January 2018 21:24
Garvin
(@garvin)
Owner Admin

Evert I think this post has the best information about Light Pattern springs:

https://forum.vintageairgunsgallery.com/vintage-bsa-resources/vintage-bsa-lincoln-jeffries-technical-tips-faqs-2/#post-510

 

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Posted : 29th January 2018 15:36
  
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