G&G rebuild - protruding bearing!

[DanBow]

Springs are cheap enough, I wouldn't bother cutting one

Just an afterthought, G&G use 160mm springs but every aftermarket one seems to be 175mm. Unless I fit something like an M80 and hope that with it being compressed to 160mm makes it equivalent to an M100/90/95. I don't think the actual spring rating is that important as long as it's at the right fps. Not sure if rate of fire would be changed with it being a "weaker" spring but, again, will compressing it not affect that????

My head is about to fall off! I'm going for coffee!

 

[Sewdhull]

Do you have a bearing on the cylinder head? If so you don't need the one on the spring guide. I cant recall how much i lost, ill go hunt down the post

 

[DanBow]

Do you have a bearing on the cylinder head?

No.

 

[Sewdhull]

Ultimately the thing that determines the strength of the spring is the force needed to compress it when installed and compressed in the cylinder.

You can have a long weak spring that gets pre compressed on installation and will be the same rating as a short strong spring which gets pre compressed less. They are all of similar length with variations of up to 25mm from those I have.

No.

Then that option is not available to you.

It's not the length that matters but how it's used.

I bought a selection of AKs springs when I was trying to get the right fps on the MP5

 

[Pseudotectonic]

Just to add a note about the heatgun method, if I were to do it again I would do it in the middle part of the wider coil section (see image below)

And I wouldn't make the spacing narrower than the existing narrow parts

Because I did it on the narrow coils side and now when it compresses those coils can "bottom out" which I suspect is causing some very minor ringing noise after each shot (probably harmless, or maybe not even related)

And if you do it in the middle section you won't oxidise the end coils flats (easier to clean up in middle) nor bottoming out the end coil

And you will minimise the changes of any coils "bottoming out" by keeping some minimum spacing

 

[Sewdhull]

312   xt95

324  xt100

356  Xt105

That was on the MP5 and I lost just under 20FPS going to one bearing from 2 so they would be a bit higher with the 2 bearings.

Progressive springs are designed to have the coils close up and (they would not be progressive if they did not) you will end up with a spring that wants to bend in the middle if you heat up the middle of it to remove the springiness.

If you really want to shorten a spring don't cut any off, pop it in a cup of water leaving the 15mm( or whatever you want to shorten the spring by) poking out and heat up the end with a propane o butane torch  nice and quickly to a cherry red colour. Let it cool in the air. Then compress it on a long bolt to shorten it. You can repeat the process if you need to. I've  never really understood why people cut the spring at all.

 

[Pseudotectonic]

500C heatgun didn't seem to remove the springiness on the compressed coils on my m90

Not even if I tried to get it to settle afterwards by compressing it for a week inside a torch

It was nowhere near cherry colour tho, it did darken the bright shiny metal a little (could just be surface grease)

--

I guess the 20 FPS loss from removing the bearing is actually because the rotational friction on the non-bearing side is slowing its decompression

Try playing with a spring by hand, but twist it or keep it from spinning, the twisting itself is going to affect it wants to expand/compress, in fact you can try to compress/decompress the spring by the twisting alone

 

[Sewdhull]

500C heatgun didn't seem to remove the springiness on the compressed coils on my m90

Not even if I tried to get it to settle afterwards by compressing it for a week inside a torch

It was nowhere near cherry colour tho, it did darken the bright shiny metal a little (could just be surface grease)

--

I guess the 20 FPS loss from removing the bearing is actually because the rotational friction on the non-bearing side is slowing its decompression

Try playing with a spring by hand, but twist it or keep it from spinning, the twisting itself is going to affect it wants to expand/compress, in fact you can try to compress/decompress the spring by the twisting alone

You need 800+Celcius to anneal springs, stainless is higher.

The 20FPS loss is because the spring is less pre compressed, there's no extra friction in having 1 bearing instead of 2. I'm going to explain why because it's come up before.

If you compress a spring one end will rotate with respect to the other and if you have a bearing at one end, that end will rotate freely because bearings have less friction than the spring rubbing against another flat surface and once the bearing is rotating there is not enough force to rotate at the other end. The whole spring is not rotating, the wire is repositioning itself as it is put in torsion, so if it is fixed at one end the other rotates.

In Airsoft we have bearings not for friction issues, but so that the spring maintains its shape and does not bend to one side or the other when it gets compressed. You could fix the spring at both ends and have no frictional losses but you would still have the spring deforming as it compresses.

If you put a bearing at both ends and lets say, one bearing is a bit stiffer than the other, then the bearing with the least friction will rotate first, but the other bearing will not rotate because the force to rotate it never gets high enough since it is relieved by the first bearing to rotate. This is essentially what happens if you have just one bearing.

 Remember that if the spring is fixed at one end there are no frictional losses, as it doesn't move.

Friction also doesn't care about area, only the force and coefficient of friction. So if you have a bearing at both ends the friction is double that of one bearing, since the force at both ends of the spring is the same. If only one bearing rotates, the friction is halved. Because the angle the spring rotates is double with 1 bearing the same amount of losses occur. Both bearings need to rotate of course for this to be true.

 

[ak2m4]

I suppose common sense should have told me that a longer spring, even though a lower rating, would make it more spicy than the standard m110 spring

It's a number of variables, length yes but most important being number of coils and thickness of wire.  And as @Sewdhull says it's the N force in the 60mm or so in the cylinder.  Every gearbox is slightly different so you'll get some variation.  

1.3mm vs 1.4mm thickness makes quite a difference.  Also quality of wire.  I went through 5 Chinese companies before realising they their grade of steel wasn't good enough and in the end switched to Japanese steel.  Quite a long, painful and expensive process!  I've had my tester M110 spring now for 4 years, must be 500,000 through it so maybe I'll do a video on it soon and compare it to the new ones.

For some customers who are unsure what spring to buy I've been sending out my tester M100 spring, along with their order.  That way they can benchmark with the M100 and then either keep or return.  Just saves a few pennies for anyone strapped at the moment.

 

[Colin Allen]

Only got one bearing.

View attachment 127950

Would removing a mm or 2 make that much difference? I'm looking at shortening my spring by about 17mm? I need to drop about about 20fps.

Really grateful for all of your input too. ?

If you shorten the spring by 17mm, the power will drop immensely.  Take off a coil or two.

 

[DanBow]

Ok, I heated the end of the spring and compressed about 15 mm ish. Put it all back together and it was totally dead!! Stripped it apart, and slipped, it all went flying all over the floor! Bollocks!!!!! So reshimmed, rebuilt, reassembled and it shoots lovely but stitting at a reasonably consistent 305fps on .28s so 1.2j. Still a little spicy. It was around 320fps on .28s - 1.3j.

I've had a look but can't find a spring thats 160mm so I'll probably just heat/compress a little more. Not today though.

 

[Shamal]

@DanBowWhat a bloody kerfuffle you have whipped up mate. My cat would have had it done by now.

Lost a spring,found a spring,bearing to high,no it's not,yes it is,spring to long.....???

 

[DanBow]

@DanBowWhat a bloody kerfuffle you have whipped up mate. My cat would have had it done by now.

Lost a spring,found a spring,bearing to high,no it's not,yes it is,spring to long.....???

You dont need to tell me what a kerfuffle its been!!! ???

 

[ak2m4]

Oh my days ? you and your length obsession lol

Is the spring you fitted one you purchased from me?  If so you just grab the power just down from it.  I'm away at the moment but can sort something out soon for you.

 

[Colin Allen]

Ok, I heated the end of the spring and compressed about 15 mm ish. Put it all back together and it was totally dead!! Stripped it apart, and slipped, it all went flying all over the floor! Bollocks!!!!! So reshimmed, rebuilt, reassembled and it shoots lovely but stitting at a reasonably consistent 305fps on .28s so 1.2j. Still a little spicy. It was around 320fps on .28s - 1.3j.

I've had a look but can't find a spring thats 160mm so I'll probably just heat/compress a little more. Not today though.

Stop worrying about the length of the spring and focus on the power rating; that is what matters.

 

[DanBow]

Stop worrying about the length of the spring and focus on the power rating; that is what matters.

But how can you focus on the power rating when that changes as you compress the spring to fit it? Rhetorical question really, ill just buy lower power springs until I get it where i want it. ?

 

[Colin Allen]

But how can you focus on the power rating when that changes as you compress the spring to fit it? Rhetorical question really, ill just buy lower power springs until I get it where i want it. ?

You are overthinking it.  The power rating is what it will produce in a typical (probably V2), well set up basic gearbox.  Other variables are far more significant than the length of the spring, such as the barrel length and diameter, the cylinder type, the presence or absence of piston head or spring guide bearings, and the quality of the airseals.

Once you have a starting point of a known output from a manufacturer's particular spring, it is easy to adjust upwards or downwards.

 

[DanBow]

You are overthinking it.

Yes, I do tend to do that! ?

 

[Leo Greer]

As a note to the original question...

When in doubt, Retro Arms low profile bushings are the way to go. I've run them from 60 RPS to over 2J.

 

[Colin Allen]

Yes, I do tend to do that! ?

We had noticed. ?