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How To[mostly] Build An Svt4b

Do it yourself, kiddies

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#1 BrokenSVT

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Posted 01 December 2010 - 07:46 AM

There has been a lot of interest in these lately on the IRC, and quite a few sold out of my living room. Here's[mostly] how you can build your own. A huge thanks to Zorn for the inspiration from his thread here: http://nerfhaven.com...showtopic=18642 . Admittedly, the concepts are the same but I've found a few new tricks. This writeup only applies to the old-style(larger tank, non-lever trigger) 4B. The concepts are similar with a lever trigger model, but relocating the OPRV will require some thinking on your own, as the 1" coupler doesn't fit the rear of the new tank.

Materials:
4B
1" PVC Coupler
1" to 3/4" PVC reducing bushing
1/4" OD, 1/8" ID vinyl tubing, about 8" for good measure.
A small section of 1/4" ID tubing as a coupler, or a nifty brass/PVC barbed fitting.
3/4" to 1/2" PVC slip fitting. I only buy the ones at Lowe's, they're meant for 4Bs.
The new pump. I use Schwinn typically. This writeup shows a MS pump.
Super Glue. I use Gorilla brand.
Oatey's red can PVC/CPVC/ABS cement. I put that shit on everything.
Epoxy putty.

Let's get started. Here is the blaster.
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Open it up via the 10 screws. If you're going to minimize this thing just hack, gouge or chew your way through the orange ring at the front of the blaster. If you're going to keep it intact, be a bit more careful(or buy an intact ring from me, I've been saving them).
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See these pieces?
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Get rid of them. You'll end up with this after using your hacksaw or razor saw:
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Debur those edges, you don't want chunks of plastic in your airtank later. Now that our tank has gone on a diet, let's get it ready for its new pump. Here's the rear of the tank before and after removing the stock check valve:
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Sorry, no bonus points for a pretty circular hole here.

Now, drill a hole near the front of the tank. I use a 1/4" drill bit for my favorite 1/4" OD, 1/8" ID tubing, and always make the hole forward-facing and oriented toward the "bottom" shell of the blaster. Debur this hole as well.
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Take the opportunity now to do a final deburring of all holes and cuts we made in the tank. Rinse it thoroughly with water, running your faucet or bottled water into the nozzle of the tank(which you should be holding OPEN, derp), and letting the water exit the rear of the tank where you cut-out the stock check valve. Shrapnel in your airtank is bad, mmk?

Let's relocate that OPRV. After much trial and error, I've settled on my favorite method. The stock OPRV is in the pump head, as with many nerfy air blasters. Cut off the pump shaft 1/2" or so above the pump head. Discard the pump handle, unless you have some other use for it. Remove the oring from the pump head(OPRV, for our purposes) and toss it in the parts bin or garbage.

Test-fit this assembly into the rear of our 1" to 3/4" bushing. It needs to go through in this manner for strength. If it doesn't fit through the bushing easily, trim the bushing's rim until it does. Super glue it to the bushing, being careful to not plug the two holes in opposite sides of the OPRV. Once it has cured, Goop the living hell out of the rear portion, being careful to not plug the hole on the bottom of the OPRV(I super glue a portion of larger vinyl tubing around the hole to build a wall).

Here's your end result:
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Edited by BrokenSVT, 01 December 2010 - 11:48 PM.

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#2 BrokenSVT

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Posted 01 December 2010 - 07:48 AM

1" PVC couplers fit the rear of the stock 4B tank like a glove. I'll let you guess what happens next. Oh, and VENTILATE your work space before this goes down.
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While you have the red can out, go ahead and attach the 1/4" OD tubing to the hole we drilled earlier. I use super glue to tack it into place, and follow up with liberal amounts of the PVC cement:
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Go ahead and solvent weld the 3/4" to 1/2" bushing to the front of the 4B tank while you're in there. Be careful to not get the cement into the nozzle, or you aren't balling after all this work. Leave a small gap between the tank and bushing's base, so it slides nicely over the shell's bulkhead without modification.
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The rest is up to you. If you want to minimize your shell, go for it. Pick out your new pump and mount it however you see fit. I personally enjoy the $7 Schwinn pumps at Kmart. They move a lot of air, build more than enough pressure to crack our OPRV open and are nice and compact. They also say "WIN" on them, which says enough. If you happen to use the Schwinn pump, use a 1/2" PVC coupler's diameter as a template for cutting and you won't go wrong.

Also, reinforce that trigger. I personally use Polycarbonate in much the same way Zorn used PVC in his writeup. Solvent weld it on using some Oatey's red, clamp it and let it cure well.
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You may need to trim the rearmost bulkhead in the shell, to clear the OPRV housing slightly. You will need to drill two holes to pass your vinyl tubing through, to the pump. I attach another length of 1/4" OD tubing to the pump before mounting it, then use 1/4" ID tubing or a barb to couple the two pieces of tubing.

Here is our guinea pig after finishing up the details. This one was ordered with a Magstrike pump and minimization that kept the handgrip intact:
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The original SVT4B
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Closing comments:

Obviously this adds a small amount of volume to the 4B tank. If your host might get pissed about that, don't tell him...or just dont' build one. The stock OPRV is maintained, so it's still "just" a 4B, but it has a bit more air to push around.

I wouldn't call this a novice mod, as parts of it(reinforcing the trigger comes to mind) will require you to measure and machine your own parts. Outside of that, it's a fairly basic build.

I hope everyone enjoys this writeup and uses it to make their own 4B.

Edited by BrokenSVT, 01 December 2010 - 11:50 PM.

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#3 nerf mafia

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Posted 01 December 2010 - 09:25 AM

I've been on the battle field with these many times, they are very impressive, but haven't become any form of advantage. I have a 4B done by brokensvt (not using these methods) and I love it, his work is very clean aswell as original.



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#4 cheyner

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Posted 01 December 2010 - 11:33 AM

That is great work. I really like your method of keeping the stock OPRV. I have been waiting for something like this to give me the boost I needed to finish my double 4B.
I also like how crazy easy it is to do a tank expansion with this method.
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#5 BrokenSVT

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Posted 01 December 2010 - 11:42 AM

Haha, thanks! Yep Cheyner, you're really only limited by how much PVC you want to add, if you want a big expansion. That, and the cost of a second 1" coupler.
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#6 Kid Flash

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Posted 01 December 2010 - 11:50 AM

I have one of these, and I can leave welts on people using marshmallows. It also shoots through cardboard with them... lol
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#7 Talio

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Posted 01 December 2010 - 01:32 PM

NJ wars will totally not allow this, but I like that you put a bike pump on it. How many pumps does it take till it's full?
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#8 HasreadCoC

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Posted 01 December 2010 - 01:43 PM

NJ wars will totally not allow this, but I like that you put a bike pump on it. How many pumps does it take till it's full?


You won't allow it because it's pump replaced? Or because it's slightly expanded? The pump I don't see as much of a problem as long as the stock OPV is left intact, the expansion.....well, in this case it's not a problem (because it's only minorly expanded), but I COULD see some idiot making it, say, 3x it's normal size (TWSS!) and singling it. Then it would make sense to ban it.
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#9 NerfGeek416

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Posted 01 December 2010 - 01:54 PM

BBBBs are borderline overpowered as it is, so it might make sense to ban this. Doing this mod, and a tank expansion, to a MM might make more sense, as the MM has a fairly small tank.
Great mod though, it looks very clean and professional.

Edited by NerfGeek416, 01 December 2010 - 01:54 PM.

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#10 utahnerf

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Posted 01 December 2010 - 01:56 PM

So how much more range does the expansion produce?
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#11 Buffdaddy

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Posted 01 December 2010 - 01:59 PM

It should be noted that New-style Big Blasts have smaller tanks to begin with, so if you had one of those, I'm pretty sure the tank expansion would be fine. As long as you aren't going nuts, anyway.
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#12 Daniel Beaver

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Posted 01 December 2010 - 02:15 PM

Good writeup! The Big Blast is a great platform for modifications, and this writeup should be on everyone's short list of practical mods. Is the pump pictured at the very end a K-mart bike pump? If so, you have made a wise choice - that particular pump is very effective for pumping up nerf guns. Cheap too, about $10.

Talio's reservations are well founded. Several of the U3 and myself have built very similar blasters, and there were some issues with slow air release. The OPVR doesn't let out air as fast as you might think, so it was possible to get off very powerful shots immediately after a bought of furious pumping. At a very large war with undisciplined players, you might have issues. But, perhaps some aspect of this mod has alleviated this problem.

When the pump handle is completely extended, how far away is it from the grip? And also, how far away is the pump handle from the rear of the blaster? I always found my own Big Blast with a pump replacement ungainly to use, due to the over extension of my pumping arm

It should be noted that New-style Big Blasts have smaller tanks to begin with, so if you had one of those, I'm pretty sure the tank expansion would be fine.

I'm not sure how true that is, given that the front of the tank has been expanded. It might be worth filling the tank with water and measuring the volume.

Edited by Daniel Beaver, 01 December 2010 - 02:16 PM.

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#13 BrokenSVT

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Posted 01 December 2010 - 02:39 PM

I'm responding from my Blackberry, so pardon any fail typing.

Talio: Typically 4-5 pumps makes for adequate pressures and ranges, and 6.5-7 to pop the OPRV.

All others, I'll try to address any concerns.

You can complete the same mod without the expansion by sawing off the hex portion of the bushing, and inserting the OPRV assembly from behind the 1" coupler. This effectively pushes the assembly within a fraction of an inch of the stock check valve's location.

The pump stroke on these miracle $7 Schwinn pumps is about 5"(working from memory), so they're not at all ungainly to use.

I've performed the same modification on a lever 4B, and will report that expanding the tank on those yields more amazing results due to the larger front chamber.

To whomever asked about ranges, I ask this: How far do you want it to shoot :rolleyes:
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#14 lionhawk

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Posted 01 December 2010 - 02:55 PM

Very nice and clean mod svt. Now I really need to save up the money for that 4 b we have been talking about.
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#15 Buffdaddy

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Posted 01 December 2010 - 03:26 PM

I stand corrected, it seems. In any case, that's really Effeminate.

Also, just saying, if you want real style, the LEGO version is on sale for normal 4B price for the holidays. Definitely going to do this once mine arrives.
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#16 Abyss Mods

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Posted 01 December 2010 - 04:26 PM

NerfGeek416: The MM may have a kind of small tank, but mine (green version, OPRV, 14 inch cpvc barrel) destroys nerf boxes, even with slugs.

Very nice writeup! I'm going to be doing this when I get a BBBB.
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#17 BrokenSVT

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Posted 01 December 2010 - 04:30 PM

Buffdaddy: Stay tuned for my most effeminate build to-date soon, involving a Lego model 4B.
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#18 Talio

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Posted 01 December 2010 - 06:34 PM

NJ wars will totally not allow this, but I like that you put a bike pump on it. How many pumps does it take till it's full?


You won't allow it because it's pump replaced? Or because it's slightly expanded? The pump I don't see as much of a problem as long as the stock OPV is left intact, the expansion.....well, in this case it's not a problem (because it's only minorly expanded), but I COULD see some idiot making it, say, 3x it's normal size (TWSS!) and singling it. Then it would make sense to ban it.


For sake of argument I'm not going to allow it because I said so.
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#19 jakejagan

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Posted 01 December 2010 - 06:43 PM

Well, if you are using slugs darts, they generally max out at a certain range (about 120 in my range tests).

I own one of these bad boys and It takes about 1-2 pumps LESS than a normal 4b while the pump is in the front.
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#20 ChaosPropel

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Posted 01 December 2010 - 06:58 PM

That's super sweet, Broken!
How far into the 1"-3/4" bushing does the "OPRV" go? Does it just go in untill it touches the groove?

Edited by ChaosPropel, 01 December 2010 - 07:05 PM.

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#21 TxNerfer

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Posted 01 December 2010 - 07:04 PM

Broken, you already know how much I love the creamsicles that you do. Keep up the good work.
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#22 BrokenSVT

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Posted 01 December 2010 - 07:38 PM

That's super sweet, Broken!
How far into the 1"-3/4" bushing does the "OPRV" go? Does it just go in untill it touches the groove?


You should insert the OPRV from the rear(or bottom) of the bushing(opposite the hex end).
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#23 shardbearer

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Posted 01 December 2010 - 08:48 PM

I like it, and the paintjob is awesome. Would it be possible to get the pump under the barrel and completely inside the blaster, with only the handle sticking out?

This gets halfway to my awesome 4B idea. Just imagine this thing, with everything inside the shell. Including the barrel.
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#24 BrokenSVT

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Posted 01 December 2010 - 10:16 PM

I like it, and the paintjob is awesome. Would it be possible to get the pump under the barrel and completely inside the blaster, with only the handle sticking out?

This gets halfway to my awesome 4B idea. Just imagine this thing, with everything inside the shell. Including the barrel.


Absolutely not. If you've seen the internals of these things, the shell is a tightly-filled space. You could force the internals to the back of the shell using my tecnique and save space at the front of it I suppose, achieving the internal barrel.
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#25 Kid Flash

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Posted 02 December 2010 - 09:33 PM

Hey, you could minimize the rear shell too, using this mod! Cool beans.

Edited by Kid Flash, 02 December 2010 - 09:38 PM.

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