Spring Trimming

Try mechbox.com - they have lots of video guides on opening up gearboxes.

Here's the one you want for an AK -

http://www.mechbox.com/site/mechbox-upg ... video.html

H.B.,
If you get as far as stripping the mechbox down and want to trim the mainspring, here are a few tips on spring trimming. Bear in mind you may have to trim/ re-assemble/ chrono and if still too high fps.. repeat.
The mainsprings are quite hard so they are best trimmed by holding the coil you want to trim against the edge of a bench grinder. Only trim off about two coils to start with. do not leave the trimmed end like it is, you need to close the end coil down until it touches the next coil. ( it should look like the end that you haven`t trimmed. To do this ..put the spring in a vise with about the last 3 coils protruding from the vise, next heat the end (cut) coil with a blowtorch until a dark red colour then tap it towards the next coil with a hammer until the two coils touch/ then remove from vise and quench it in cold water. Both ends of the spring should now look the same.
I hope this makes sense.
I have been repairing/ restoring/ tuning air guns for the last 28 years and have always used this method to good effect.
ftj

Ah, that's how you do it - I've attempted to do it in the past using pliers and got nowhere obviously!
This has meant over the years I've ended up with a pile of spings that I neglected to label, so here is a sub-question for you:
How can you measure the power of a spring without a) an engineering shop and b) strip, build and chrono and gearbox repeatedly with various springs?

Chommers,
You can mearure the compression poundage of a spring if you have a `sring balance guage` or something similar, such as the spring balance used by anglers to weigh a fish that you have caught. Obviously the weight range of the guage would have to be within the limits of the spring you are trying to measure. SIMPLE REALLY... NOT.
You also need a length of strong cord, a metal rod and a vise.
However a simpler, though not quite as accurate method is to use your bathroom scales. Place the end of the spring on the scales ( scales must be on a firm smooth floor, not carpet.) next place a block of wood or similar on the uppermost end of the spring and press down on it until the coils of the spring JUST touch one another. the spring is now fully compressed. Now read the weight in lbs. or kg. ( whichever ), this is the poundage of your spring.
Unfortunateley this will not tell you what f.p.s you can expect from your weapon, this can only be done by trial and error. However if you make notes of all your spring poundages then test them in one gun and note the fps, you can build up a database for future reference. Now when you buy a spring in the future you can test it`s poundage on your scales and this will give you a rough idea of the fps you can expect. Although I have to say that there are so many other variables involved with a guns internals that this is not an exact method. The manufacturer will have done a lot of testing initialy to get the correct performance from the gun before production starts in earnest. Now you see one of the reasons they ( guns) cost so much.
That wasn`t much help was it. !!!!
ftj

I've got another spring related question, (rather than start another thread I thought I'd ask it here), if I want to increase the fps will packing the spring with spacers, (i. e. pre-loading them), work? It's something I've done with forks on motorbikes to stiffen up the front suspension.

I would go for the bottom spring guide,already got spacers and alot better than the standard one at the top,and to trim springs i use wire cutters in the picture,its hard to tell what fps the springs will do ,theres so many of them,they all perform totally different from each other and also depends on the gun.i only fit systema springs.-- attachment is not available ---- attachment is not available --

Hi all,
Using spacers can sometimes work , but not always. The thing to bear in mind is this .. there has to be sufficient space inside the compression cylinder when the weapon is fully cocked , i.e. when the piston is fully to the rear and locked by the sear. The space now taken up by the mainspring/spring guide etc. ( That`s everything behind the piston head measured from inside the piston and to the rear inside of the mechbox ( if we are talking airsoft), is a fixed amount of space / length. Now if the mainspring is ``coilbound``, that is all the coils are touching one another when the gun is cocked, then there is no more room for any spacers or a longer spring
Most airsoft guns, as standard have plenty of room for a longer mainspring or spacers, but just be careful of the amount of room you have for any `uprated` spring or spacers. All spring powered airguns work better if the mainspring is not totally coilbound when cocked.
I could go on for hours about performance enhancements in airguns ( airsoft guns are also airguns) but I will say this `the spring is only one factor in the power equation`.
I can tell you that certain makes and models of air rifle can give higher fps and be smoother to shoot and more accurate by SHORTENING the standard mainspring.. oh yes.
ftj

Guys... as ever THANK YOU for all the amazing help!

I'm know already thinking that 'hey we could really trick this baby out' as well as fixing the spring!

Hey, FTJ - I'll give the bathroom scales trick a go. I see what you mean - start with a 'known' value then the rest can be compared to it. Nice one!

Springs are cheap at ehobby asia, I have had a few go coil bound so putting spacers on may lead to youy gun jamming, the PDI 130% or systema M100 is a good safe bet to give you a upgrade & stay legal

http://stores.ebay.com/eHobby-Asia-Airs ... idZ2QQtZkm

Steve.D