Proper protocol for replacing a broken mainspring.

[Leonardj]

I have often been criticized by some springer "experts" with regard to my insistence on doing a complete teardown and cleaning of all internal powerplant parts when replacing a broken mainspring. Many of the "experts" consider the extra work involved as superfluous and un-necessary. Hopefully the following pics and info will convey just why I maintain that a full and proper cleaning is indeed necessary.

I have seen more than the average number of broken mainsprings over the decades that I have been working on airguns, and the breaks range from simple to complex. To define these terms, a simple break will appear almost as though the spring was cut off by a rotary cutter, and is usually quite a clean break. On the other hand, a complex break can occur over a lengthy portion of the coil - in some instances a full half of the coil, which can result in producing a significant amount of debris within the gun. The following pic shows just such a complex break in a mainspring.

http://i649.photobucket.com/albums/u.../LongBreak.jpg

While these two broken pieces can be fitted together, and may appear to be complete, this is not the case. During the course of this complex break going from a fracture to a full break, tiny, hardened steel flakes break away from these fractured edges each time the spring goes through a firing cycle of compression and extension. These tiny bits of hardened steel debris are caught up by the lubricants, and subsequently spread throughout the powerplant, and in some cases, down into the trigger mechanism. Thus, if allowed to remain in the gun, what will eventually happen is that these tiny bits of hardened steel will become embedded in either the powerplant walls, or the rear skirt of the piston, both of which are generally a softer grade of steel than the mainspring fragments, and will cause galling to these softer steel parts, to varying degrees. I have even seen some of these tiny fragments work their way into the piston seal, becoming embedded into the side of the sealing lip, and causing the seal to blow by. This then results in another (seemingly unrelated) repair, that was completely avoidable with a little bit of extra effort while the gun was apart for the mainspring replacement.

The following pic shows just how much hard steel debris resulted from the complex break shown above. This is just what I was able to retrieve when wiping the cleaning tray out with a paper towel. A lot of the really tiny stuff was poured out with the cleaning agent. The red circles outline some of the heavier concentrations of the debris, while the yellow arrow indicates a small piece broken away from the mainspring guide. Note the one rather large fragment in the lower left quadrant of the top red circle. Something that size has the potential to cause significant damage if allowed to remain.

http://i649.photobucket.com/albums/u...ringDebris.jpg

Admittedly, while a simple break may presumably produce less debris, there really is no way to be absolutely sure - thus IMO, it is simply not worth the gamble for the minimal amount of extra time to do the job properly.

[Airsporter1st]

All makes good sense.

[Garvin]

Very interesting, Len, thanks. I'm now completely terrified and am trying to think back to what I may or not have done in terms of lubes replacement going years back!

For those who don't know, this summer Len became the reigning Canadian FT champion. So he's a crack shot as well as being a forensic airgun engineer (and a very decent photographer).

[oliver13]

I always have a look around & a re lube when I've got the spring out, just to check it all OK, it would be stupid not to.

[Airsporter1st]

Very interesting, Len, thanks. I'm now completely terrified and am trying to think back to what I may or not have done in terms of lubes replacement going years back!

For those who don't know, this summer Len became the reigning Canadian FT champion. So he's a crack shot as well as being a forensic airgun engineer (and a very decent photographer).

He's also got a lovely range (in his back garden?) - looking at his photos.

[UrbanFox]

Good grief, why on earth, would you not do a through clean, with a broken spring? Makes sense to me Len.
Some interesting photos there.