A&K SR25 and normal gear set ....

[conger]

Hi folks,

 

Crazy idea perhaps but interested in your opinions ...

 

A&K SR25 uses elongated v2 mechbox, longer piston and sector gear with 19 teeth instead of the 16 teeth a normal sector gear has?

 

I believe the bevel and spur gears are common between normal v2 gearbox and extended v2 gearbox ...right?

 

I'm aiming for reliability and quietness and looking at helical torque up gears as a potential upgrade.

 

I do not need higher rate of fire.

 

CA sells torque up helical gears for SR25 so the solution appears covered ... but at my last look through the various internet shops, there seems to be alot of "Out of Stock".

 

 

Now acedamically, if with using a spacer behind the spring guide [assumuing secure placement and me turning a piece of Alu for the job] to compensate for the loss of sector gear teeth, and using a normal v2 sector gear, would the loss in piston stroke be outweighted by using a slightly more power spring [i'm not looking for mad high FPS here] which is fully compressed before release.

 

Put another way, could I expect to operate similar to a normal v2 gearbox?

 

If this were possible, it opens up the spare parts market much more widely for me than the presently limited SR25 offerings. I've not got great faith in CA internals!

 

Edit: Mods apologies for put this in the wrong section

[AnotherJesus]

Well, what you've mentioned seems overly complicated to me. If you're useing a URX, before you'd even mentioned about changing the gear set I'd have said shorten the stroke of the piston. Those things have way to much volume for the barrel length. But once you're onto useing a longer barrel, it's not so much a problem. Especially with heavy ammo. Although still, you're getting much more energy creep from useing heavier ammo than a normal AEG would.

 

If you think the gear set upgrade is worth while, do it. In my experience of SR-25 gearboxes, it's better to have a shorter cylinder than they use. I'd also suggest you swap out the piston for a standard AEG piston, and use a spacer before the piston head to get the right engagement. Don't worry too much about changing the spring yet, because you don't know what effect it'll have on the FPS. These long gearboxes often need more powerful springs than a normal AEG gearbox to get the same FPS, because of the poor matching to the barrel capacity.

 

When I look at the SR25s available, it makes me think how poorly the companies like CA and G&P understand the TM gearbox design they initially copied.

[Docv400]

I've just done this to a C.A. CA-25 (same 19-tooth piston set-up).

The FPS before the mod was around 360 (so the owner quoted).

Afterwards it was 365.

That could be down to several things; different chronos, different piston heads (I make my own, the original was a standard C.A.), or just due to the 'fresh' build.

 

All I did was fit a Marui piston with my own-make piston head (extended length to set AoE and compensate for the shorter piston), and took three teeth off the sector gear, everything else was as it was beforehand.

 

It was the Carbine version, and as AnotherJesus mentioned, there's more than enough cylinder volume for that length inner barrel.

I think the pre-loading on the spring will compensate a lot (or possibly entirely) for the lost stroke of the shorter piston.

 

I've found this on the L85 conversions I've done as well.

[MDK_Marshal]

I'm aiming for reliability and quietness and looking at helical torque up gears as a potential upgrade.

 

As others have dealt with the rest of your post, I'm going to deal with this bit.

 

Helical gears aren't significantly quieter than normal gears, are a pain to shim properly, and offer no discernable advantage.

 

All the noise from the gears is drowned out by, well, everything else going on in the gearbox, so the extremely small reduction in volume from the helical gears is never noticeable, as the rest of the drive train is much louder, and the piston smacking forwards adds a fair amount of volume too...

 

Best to stick to regular gears, IMHO. Cheaper, easier to shim, and just as quiet in a real-world application.

[conger]

Hi folks,

 

MDK_Marshal ..... helical shimming hmmmm! I wasn't thinking of this! Good point. Noise will be an uphill battle too.... sorbo pads and better field craft I guess

 

Helical is advertised as having better torque properties which from a reliability point is attractive to me. I'm OK with shimming straight cut gears ..... helical shimming is perhaps a new challenge .... Hmmm I dunno!!

 

Docv400 ... your post kinda gives me the motivation to try this now anyway. My inner barrel is 509mm but perhaps with a TB inner barrel and good air seals in the line will help it work.

 

AnotherJesus wrote: These long gearboxes often need more powerful springs than a normal AEG gearbox to get the same FPS, because of the poor matching to the barrel capacity.

 

Bang on! This is also my central thinking here. Currently, I'm at 350 FPS. My club allows 500 FPS with conditions. 450 FPS is where I'm most comfortable at. A spring change is planned. I want to minimise cost on reliability and wear however when pulling it.

 

In any case, I think it'll be ok ...

 

Having some torque overhead and a smooth effecient transmisson is the aim. I can pull a slightly more powerful spring with relative ease and less stress on the drivetrain.

 

Maybe I'll just wait for the CA torque gears for SR25 to become available again!

 

However, if I do this, I'll comment back my experience and results.

 

Cheer all

 

 

 

[conger]

Sorry to double post .... ran out of edit time ....

 

Can anyone confirm that the V2 normal gearset and the A&K SR25 gearset [extended V2] are the same apart from the number of teeth on the sector gear?

 

Thanks

[Sale]

I can't confirm about the A&K elongated V2 gearbox specifically, but in every other AEG it works.

 

What Docv400 wrote is basically your ticket. No need to add spacers to the spring guide: just a 10–15 mm spacer between the piston body and piston head is what you need, and the FPS will be pretty much what it was before with the same spring. The stroke is shorter, yes, but the spring has more tension as well because of the spacer. With your 509 mm inner barrel you won't need all that stroke length anyways.

 

Parts list as I would see fit:

 

- Upgrade gears of your choice (for regular AEGs)

- Upgrade piston of your choice (for regular AEGs)

- 10 mm (minimum) to 15 mm (corrected AoE) spacer to place in between the piston head and piston body

- Longer M3 screw to attach the piston head

 

If you're happy with the velocity you have now, stick with the current spring. If you want more, this setup will provide roundabout the same performance as with any AEG.

 

Regarding the choice of gears, I've found good quality gears with helix cuts to be quieter than flat ones, although with a good shim-job the flat ones are already very quiet. However a set of CA steel helical gears I bought a couple of years back aren't nearly as quiet as the Systema ones I've installed. It boils down to shimming more than anything, quality more than gear type, but even after these there's also a slight reduction in gear sound with helicals in my opinion.

 

-Sale

[Docv400]

If you go with the spacer option (between the piston head and the piston), make sure to align the head with the piston carefully.

Piston heads have a boss on the back that locates in a hole in the front of the piston, ensuring that the head is perfectly central in relation to the piston.

If you fit a plain spacer, you won't have that boss, so take your time and get it aligned.

You can check it by fitting the cylinder in the gearbox shell without the cylinder head in place.

Fit the piston, with the piston head attached (but not fully tightened, just tight enough to hold it in place), and have the piston all the way rearwards (no spring fitted).

If you look into the cylinder through the opening at the front of the box, you'll see if the head is concentric with the cylinder, the gap around the head should be even.

Adjust it if it's out, then tighten the screw fully and re-check.

 

I make my spacers with a boss, and a matching bore for the boss on the piston head.

 

Do you know how to measure up to get the correct spacer length, taking into account the Angle of Engagement setting?

If you're unsure, give me a PM with your e-mail address and I'll e-mail you an explanation/guide.

[conger]

folks,

 

Many thanks ....

 

In about 2-3 weeks I'll hopefully post back with my experience to close off this thread.

 

Docv400, again cheers to the notes ... this was kinda why I thinking of putting the spacer behind the spring guide to begin with. But, now I think I'll follow the experience!

 

Sale, cheers also for your comments on the gear set.

 

I have a stopover in HK at the mid of Sept so I'll be taking full advantage of it to pick up some small internal parts hopefully.

 

Cheers

[Docv400]

You'll have a great time in HK, it's Airsoft heaven .

Try and meet up with one of the HK Arnies members, if you ask nicely you might find one of them will show you around.

It's very handy having a local guide with you.

I had three of them with me when I was there in 2006

Make a shopping list and try to stick to it, it's really easy to get carried away with all the stuff available.

[conger]

Cheers. I'll have literally a few hours in the middle of a Thursday the afternoon hopefully ..... so it's going to be a surgical strike at the AS shops. I have a few wishlist items from some friends and my own list of wishes.

 

Maps prepared, some shops emailed.

 

I just know I won't have the time I really would like to have but hey, it's all good.

 

Doc, many thanks for your help and assistance especially... and indeed to everyone above.

 

Much appreciated

 

 

[banjo]

Just to help everyone out, if they are planning on doing the same to their SR 25 and don't have the lathe fasilities of Docv400..... I used a spacer ready made for converting the standard length L85 piston to the long length GB, I bought mine from Airsoft World in Scotland, it comes with a long bolt and is ready to accept any normal piston head, but the AOE still needs correcting after its fitted And I replaced the sector gear with a stock V2 sector gear. The GB is still quite noisey but I think this is due to the sh1te QC of A&K gears

 

And for those worried about the short stroke issue, I worked out that once the AOE is corrected, the spacer fitted, etc. etc. the cylinder volume is ideal for a 6.04mm x 509mm barrel

 

Hope this helps

 

B

[Docv400]

Cheers. I'll have literally a few hours in the middle of a Thursday the afternoon hopefully ..... so it's going to be a surgical strike at the AS shops...

Even more reason to have a local 'guide' with you

Post a request on this topic;

Airsoft shopping in HK

 

[conger]

Just closing off this post later then expected!

 

After all the above discussion, I spent alot of money on gearsets, bore up cylinders, inner barrels and the long list of other stuff. Bank Account

 

I'm feeling a little guilty to be honest that I've decided not to do the project now but I have learned alot just from the discussion.

 

I've fitted a CA helical super torque up SR 25 gearset.

 

I decided against the normal gearset and spacer mod in the end [i did the angle of engagement mod!] because having no experience with the SR25 parts that are available, I wanted to give them a shot first. If need be, I'll resurrect this project in the future if needed. I also bought some normal gearsets and other stuff ......

 

I used....

 

Madbull TB 6.04 590mm

.. Hard bucking

CA Helical Super Torque up for SR25 Gearset

CA SR25 cylinder bore up kit including nozzel

Metal bushings [no bearings]

SP170 Spring [in the elongated mech box, it's not punching it's true weight]

A selection of Guarder, G&P and Systema shims

 

Shimming took a few hours literally to get it right, but it's right .... it's nice and crisp. The bushing placement was the biggest hurdle I'd encountered. I did alot of careful placement, testing, part building the mech, testing, rebuilding until I got it correct. Motor height was the other key area once the shim job was perfected.

 

It is still a little loud for a sniper platform but it's and AEG ...... and certaintly alot quieter than before. I also built in a AB mosfet [home build] which helps considerably with stroke control.

 

~480 FPS, I've got hits out to ~75m or 80m in recent games and I'm very happy.

 

Thanks to all again for your comments and advise. Though not taken up today by me, it's there for future use and perhaps for other readers of this thread.

 

Good Hunting

 

Conger