FWB 124 mainspring length ?

[ccluck]

I'm bringing my FWB 124 Sport back into service, after years of letting it languish at the back of the vault. It shoots kinda OK, but I want to get it in top form. I've watched few videos, and read the PyramydAir 3-part blog about overhauling one of these, so I got into this afternoon. Built up a very effective DIY spring compressor and now have the spring in hand, but also have a question.
How long should it be ? The blog illustrations suggest that the spring is roughly twice as long as the endcap-guide assembly, so maybe 12i-sh inches ? Mine measures 8.75 inches. The coils appear to be uniformly spaced. the ends look to be original, not cut off or anything like that.
The blog also says there should be a lot of preload, about 4.5 inches, but this one was completely slack when the compressor was backed off only 1.75 inches.

So, can one of y'all tell me what I've got here, and what do I need to go to original specs ?

 

[ccluck]

OK, so with some additional research I've concluded that I have some version of a tune kit, similar to, if not actually, a Maccari kit. There is a delrin spacer up in the piston to provide some extra load to the short spring. Since everything looks clean and tidy, I'll just replace the piston and breech seals, lube it all up and carry on. No telling when the mod was done, but before 1995, I expect. Could have been later, but that would imply a pretty significant lapse in my memory - hate to think that's true.
Anyway, all is well, but comments are still welcome.

 

[Wadcutter]

Here's a Maccari Pro Mac kit (top), compared to factory spring (bottom).

 

[ccluck]

Yessir, that appears to be exactly what I have, although I didn’t measure the wire diameter.
Thanks for the comparison photo.
In your experience, does this constitute a perceptible upgrade ?

 

[FWB127]

With a Maccari kit fitted .177 and incredibly smooth

 

[FWB127]

 

[Hateful McNasty]

There's help or blog sites threads of whatever to help

Like here's a start

"How to measure a mainspring"

The spring-piston powerplant | Blog | Pyramyd AIR

by B.B.Pelletier Today, I'm going to do a fundamental report that I promised some time back. I'll show you how a spring-piston powerplant works. I'll also show you how to measure mainsprings so you can find replacements when yours wears out. We had a question yesterday morning from a blog reader...

www.pyramydair.com

Hw 55 Tyrolean – Part 5 How to measure a spring | Blog | Pyramyd AIR

by B.B. Pelletier Annoucement: There's a new article on Pyramyd Air's website. "How to mount a scope" includes a short intro and avery comprehensive video guide for mounting scopes on just about any airgun. On to today's blog. Part 1Part 2Part 3Part 4 With all the interest you guys have in...

www.pyramydair.com

 

[beerthief]

I think i would lightly grease the spring and put it back together , Enjoy .

 

[Hateful McNasty]

I think as said above if it's a factory uncut just coil count and coil diameter .

A fresh new going to be longer then a scragged or set spring that relaxed .. coil count and coil diameter

If was going to say a springs about 20$ +/- just get one to see and keep it handy so when you do need a spring you got it not looking and hoping the way parts are heading ..

Aldi now see there's 2 old style and new ??


Old ...
https://www.pyramydair.com/product/air-venturi-feinwerkbau-mainspring-fits-fwb-124-air-rifle?a=3665


New...

Main Spring for New Model Feinwerkbau Sport | Pyramyd AIR

We've got a great price on Main Spring for New Model Feinwerkbau Sport at Pyramyd AIR. Shop where the experts do!

www.pyramydair.com

 

[KWK]

Here's a Maccari Pro Mac kit (top), compared to factory spring (bottom).
View attachment 527600View attachment 527601View attachment 527599

How long is the spacer/top hat? Thank you

 

[ccluck]

How long is the spacer/top hat? Thank you

My kit is a little different than Wadcutter's Pro Kit. Here's what I have : spacer measures 1.160" from spring contact surface to the other contact surface, no centralizer stub. Spring is 29 coils, 8.625" length, 0.815" OD, 0.555"ID, wire OD 0.127".

 

[Sicumj]

Cut a plastic water bottle to the circumference of the spring. Wrap around the spring and install that. It cuts down on vibration considerably.