FPS woes

[Atomic]

Hey all! First off, I am good with gearboxes. I've upgraded all my AEGs and used them all summer with only 1 broken spur gear (my fault, lazy shimming) out of 3 AEGs. My over forum limits G36 workhorse never had a problem.

 

Today we have a TM G3SAS.

 

I upgraded:

Bushings: Metal Area 1000 (and reshimmed)

Piston: Area 1000

Piston Head: Deep Fire non bearing

Cylinder Head: Area 1000

Spring Guide: Guarder metal w/bearing

Spring: PDI 120

 

Stock: nozzle, gears, tappet, cylinder

 

With this, I'm chronoing around 260. I fully expected to be right at 1j. The hop is fully off. ROF seems fine on an 8.4v. It passes the finger on the nozzle compression test.

 

I have tried 2 PDI 120 springs, a stock TM piston, piston head and cylinder head in different combinations. I tried a no hole systema cylinder and my FPS dropped to 220. I suspect the nozzle, just since I don't like the 4 notches in it. I prefer Guarder nozzles. The cylinder is a 3/4 hole, but I'm wondering if a 1/2 hole would be better.

 

I wanted to throw this out to you guys, before I started ordering parts.

 

Thanks all!

[Tank]

Have you checked the compression with the gun dis-assembled?

If your compression is bad try using the piston o-ring off of the Marui piston on the Deep Fire piston head.

 

If your compression is good you may need to go to a heavier spring or a non-vented cylinder.

I know you said that you tried a Systema non-vented cylinder however, if it was a "bore up" cylinder & you are not using a "bore up" piston head then you'll loose a lot of compression. Which would explain your drop in FPS when trying that cylinder.

 

One other thing to take into consideration is that you are trying to upgrade a gun with a pretty short barrel. While a set up like this would likely produce the results your looking for in say a G36 or M4 this same set up in a G3SAS will produce lower velocity because of the shorter barrel.

[TriChrome]

Did you chrono the gun before the upgrade, and did you mess around with the hop-up bucking at all?

[Atomic]

Did not chrono prior. Booo. I checked the hop, good idea, it's fine. I also checked the compression with the gun apart. I can slowly push the piston forward with my finger over the nozzle (with the stock piston).

 

I have a new a PDI 130pro, so I put that into it and I'm getting shots around 300, but also the occasional 260.

 

I'm going to try a few other parts combinations.

 

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Off topic, longer springs are a real pain to install, since they want to buckle out as you try to close the gearbox. If the spring guide was another few inches long and went into the start of the piston, assembly would be much easier, no? Would a spring guide that long have any downsides?

 

---

 

It was the cylinder head. I'm chronoing at 304 now with the stock one.

[zentaurus]

Off topic, longer springs are a real pain to install, since they want to buckle out as you try to close the gearbox. If the spring guide was another few inches long and went into the start of the piston, assembly would be much easier, no? Would a spring guide that long have any downsides?

<{POST_SNAPBACK}>

 

can't quite get you there. "start of the piston"? near the head? start of piston travel?

 

one possible off the top of my head (and one you've probably considered already) is bumping into the piston head and thus preventing full spring compression plus a host of other problems.

 

edit: maybe you meant a few cms or mms longer?

[cllwayzata2011]

<snip>

 

---

 

Off topic, longer springs are a real pain to install, since they want to buckle out as you try to close the gearbox. If the spring guide was another few inches long and went into the start of the piston, assembly would be much easier, no? Would a spring guide that long have any downsides?

 

---

 

 

<{POST_SNAPBACK}>

With longer springs it's easier to close the gearbox with two people. Get your wife, girlfriend, or just someone else to hold the gearbox 3/4 of the way closed with the back end just open enough for you to slip the spring guide in. Put the spring guide in the spring, then slowly twist and push it in. Once you have the spring guide popped into place, tell the other person to push down, while you are pushing down on the cylinder. This will keep the spring from pushing the gearbox apart while you get everything else lined up.

[Boba_Fett]

Let´s check the compression step by step:

 

Install the cylinderhead to the cylinder, close the front of the cylinderhead with your thumb and press the piston-pistonhead assembly into the cylinder. After 2 or 3 mm there should be a solid stop.

 

If not check where you are loosing pressure. If it is the cylinderhead remove it add some silicon tape from the hardwarestore and reinstall it.

 

If it is the pistonhead re-lube the cylinder if this will not solve the problem install a TM O-ring. Change those as long you have a propper sealing.

 

Next the Nozzle. Here we have to check to sealings: The less important is the sealing on the cylinder head. Fix the nozzel with the tappet plate in shooting position not in the rear position and again press the piston assembly into the cylinder closing the nozzle with your thumb. A little bit of losing pressure is okay. If it is to much change the nozzle or get a cylinder head with a longer "nozzle barrel". Sometimes V3 cylinder heads are great in V2 guns. Longest "nozzle barrel" is at the AUG cylinder heads. This may need some adjusting to be used with V2 nozzles.

 

Next step with your nozzle: The very important one. Put the nozzle into the hopup unit and gently press it into it with your finger sealing the nozzle. Now blow into the muzzle of the barrel. There should be no loss of pressure. A little bit here is about 20% of power, a lot of loss can decrease your power to 0,5 Joule.

 

When losing pressure with a brand new hopup bucking change the nozzle. Forget about MP5/M4/P90 or what ever the names are: If it seales perfectly and is still able to feed BBs you are fine.

 

And last but not least: Anything is fine and the fps is way below what it should be: Change the cylinder grease Try using gear grease inside your cylinder...whoops...another 100 fps gone

[Tank]

If the spring guide was another few inches long and went into the start of the piston, assembly would be much easier, no? Would a spring guide that long have any downsides?

<{POST_SNAPBACK}>

 

 

Yes it would be bad.

If the spring guide is too long it will come in contact with the front of the piston (inside) preventing the piston from traveling it's full stroke. This would, of course, cause catastrophic damage to the piston &/or gears.

[Atomic]

Duh. Thanks Tank. I guess the piston does have to actually move. Poop. I thought I was on to something

 

I got it fixed. The Area 1000 cylinder head had a bad oring. I beet I took that gearbox apart 10 times to try different combinations. I will say this tho, I like working on G3s. If I had to take the body and selector apart like on an MP5 each time, I would have a lot less hair.

 

Thanks all!

 

Gonna throw out the +1s like they are $100 bills!

[Veek]

Let´s check the compression step by step:

 

Install the cylinderhead to the cylinder, close the front of the cylinderhead with your thumb and press the piston-pistonhead assembly into the cylinder. After 2 or 3 mm there should be a solid stop.

 

If not check where you are loosing pressure. If it is the cylinderhead remove it add some silicon tape from the hardwarestore and reinstall it.

 

If it is the pistonhead re-lube the cylinder if this will not solve the problem install a TM O-ring. Change those as long you have a propper sealing.

 

Next the Nozzle. Here we have to check to sealings: The less important is the sealing on the cylinder head. Fix the nozzel with the tappet plate in shooting position not in the rear position and again press the piston assembly into the cylinder closing the nozzle with your thumb. A little bit of losing pressure is okay. If it is to much change the nozzle or get a cylinder head with a longer "nozzle barrel". Sometimes V3 cylinder heads are great in V2 guns. Longest "nozzle barrel" is at the AUG cylinder heads. This may need some adjusting to be used with V2 nozzles.

 

Next step with your nozzle: The very important one. Put the nozzle into the hopup unit and gently press it into it with your finger sealing the nozzle. Now blow into the muzzle of the barrel. There should be no loss of pressure. A little bit here is about 20% of power, a lot of loss can decrease your power to 0,5 Joule.

 

When losing pressure with a brand new hopup bucking change the nozzle. Forget about MP5/M4/P90 or what ever the names are: If it seales perfectly and is still able to feed BBs you are fine.

 

And last but not least: Anything is fine and the fps is way below what it should be: Change the cylinder grease wink.gif Try using gear grease inside your cylinder...whoops...another 100 fps gone biggrin.gif

 

Thanks for this little guide Boba_Fett, very interesting I only checked the first thing (pushing the piston in the cilinder). Maybe they should make this one a sticky.

 

grtz

[interpolgunit]

Area 1000? bad o-ring? I heard a lot of people say this, but I don't think it's true.

 

It's a vented piston head, meaning there are little holes on the top. When the piston moves forward, air pushed inside the piston head and spreads out, pushing the oring against the cylinder making the tightest fit possible. In fact, I think you need little to no grease for this to occur. Maybe you have silicone sticking into the piston head hindering movement of the Oring inside the piston head?

[pke]

With longer springs it's easier to close the gearbox with two people. Get your wife, girlfriend, or just someone else to hold the gearbox 3/4 of the way closed with the back end just open enough for you to slip the spring guide in. Put the spring guide in the spring, then slowly twist and push it in. Once you have the spring guide popped into place, tell the other person to push down, while you are pushing down on the cylinder. This will keep the spring from pushing the gearbox apart while you get everything else lined up.

 

Or try drilling a hole in the front end of the spring guide, and insert a long screwdriver thru the hole, from the back of the gearbox. That should keep the spring under some control. While you put the gearbox together.