Compression Test

T_A_N_K · December 27th, 2008, 15:53

What is happening is that the oring on the piston head isn't creating a proper seal with the cylinder. You can try taking the oring off, lube it and stretch it to see if that works. If not, try using the stock oring or swap your cylinder.

Once there is a good seal, you need to make sure your nozzle is sealing properly. Most quality nozzles have a oring inside, I recommend taking it out, use needle nose pliers or a dental pic, and again stretch and lube it.

Once this is done, attach the nozzle to the the tappet plate and place it on the tip of cylinder head, make sure that nozzle is not completely seated on the cylinder head or it will create a false seal. Once you do that use your hand to hold the tappet plate against the cylinder, cover the nozzle with your finger and do the compression test again. if your nozzle, and piston head are sealing properly it should be very difficult to push the piston in.

You don't need expensive brand name parts like Prometheus to make it work. If I have a $20 Prometheus nozzle and its not sealing and a $5 no name junk nozzle seals, I'm going to use the junk one.

[]D[][]\/[][]D · December 28th, 2008, 02:22

I'm using the stock piston head and cylinder. The only aftermarket parts I got was a cylinder, spring and air seal nozzle to compensate for my longer inner barrel that I just installed.

How much resistance am I supposed to feel during the compression test? Is being able to push the piston forward in the cylinder using quite some force good or am I not supposed to be able to push the piston forward at all? Because it's difficult to push the piston forward in the cylinder but I can eventually push the piston all the way to the cylinder head.

I'm just kind of confussed because one guy is saying that you're not supposed to be able to push the piston forward in the cylinder at all and another guy is saying that it should be difficult to push the piston forward in the cylinder.

Styrak · December 28th, 2008, 02:53

Quote:

Originally Posted by []D[][]\/[][]D

How much resistance am I supposed to feel during the compression test? Is being able to push the piston forward in the cylinder using quite some force good or am I not supposed to be able to push the piston forward at all? Because it's difficult to push the piston forward in the cylinder but I can eventually push the piston all the way to the cylinder head.

In a perfect world it would have a perfect seal. But if it's very hard to push in, it's still OK.

T_A_N_K · December 28th, 2008, 04:25

The idea is that you not suppose to be leaking air. When you push the piston in your compressing the air, if you don't hear a hissing noise or anything then your fine. For the most part you should be bale to push the piston in 1/3 to 1/2 with resistance, till the point there is a lot, that's what you want. What will happen if you have a good seal is if you push any harder your cylinder head will pop off, however since its held in place by the mechbox it isn't the problem.

[]D[][]\/[][]D · December 28th, 2008, 21:48

Yeah, I replaced the parts that I bought back with the original TM cylinder and air seal nozzle. Now I know what you guys meant when I did a compression test with those components. So basically, the spring is now the only upgraded part. When I went to chrono the gun, I was shooting around 350-360 FPS on 0.25g BBs with the new MS110 spring.

Also, when I compared the Prometheus Air Seal Nozzle to the stock TM Air Seal Nozzle, I noticed that the Prometheus is shorter than the TM. Could this also have played a factor in why my FPS was below 200 before? The Prometheus Air Seal Nozzle I purchased was meant for the AK47 series and I was using it in my SIG SG 552. But I have an AK47 inner barrel in my SIG SG 552, that was the reason why I got it. Should I have just gotten the one that's made for my gun?

T_A_N_K · December 28th, 2008, 21:53

You want to get the correct nozzle for the correct gun. Although you bought an AK length barrel, it doesn't mean your gun is an AK, it just has a longer barrel. Nozzles look similar but there are differences in them for a reason. Really the only family of guns that have interchangeable nozzles are the armalite series, some AK's, and a few others. Otherwise, pretty much everything else out there has their own specific nozzle.

Styrak · December 28th, 2008, 22:25

Quote:

Originally Posted by []D[][]\/[][]D

Also, when I compared the Prometheus Air Seal Nozzle to the stock TM Air Seal Nozzle, I noticed that the Prometheus is shorter than the TM. Could this also have played a factor in why my FPS was below 200 before? The Prometheus Air Seal Nozzle I purchased was meant for the AK47 series and I was using it in my SIG SG 552.

Oy. YES it definitely would matter. Nozzles are gun-specific. It wasn't making a proper seal with the hopup rubber because it was shorter.

And this is why there are gun doctors...

T_A_N_K · December 29th, 2008, 00:40

Yeah I forgot to mention Styrak is right, if its too short the nozzle won't seal, if its too long, then your gun won't feed properly. Thus why need to get nozzle specific to your AEG.

Kos-Mos · December 29th, 2008, 02:16

/thread

There you go. Inner barrels are made a certain lenght. If I use an M16 innerbarrel in my G36, it does not mean I have to use the M16 nozzle. It just means that I am using a 509mm long barrel.

You can use a PSG-1 barrel in an MP5K if you like to. You will still need an MP5 nozzle, since the hop-up unit and the way the gun is made needs that specific nozzle to work.

F34N0R · December 29th, 2008, 02:43

As for the sorbo pad, it has nothing to do with proper sealing but only decreasing stress of the impact.

350 fps with 0.25gr bb & ms110 spring is good.

[]D[][]\/[][]D · December 29th, 2008, 10:56

Quote:

Originally Posted by Styrak

And this is why there are gun doctors...

Yes, I know that. But I have really good mechanical/building skills from working on cars all day and building custom computers on the side. I just want to know how to be able to work on my airsoft gun myself.

A wise man once told me, that you don't learn anything if you don't make mistakes.

[]D[][]\/[][]D · December 29th, 2008, 10:59

Quote:

Originally Posted by F34N0R

As for the sorbo pad, it has nothing to do with proper sealing but only decreasing stress of the impact.

350 fps with 0.25gr bb & ms110 spring is good.

I just reinstalled the Systema N-B Cylinder Type 1 that I originally purchased since I found out that it was the nozzle causing the low FPS and now I'm shooting at 370-380 FPS on 0.25g BBs.

m102404 · December 29th, 2008, 11:03

Making mistakes is human...learning from them and not repeating them demonstrates wisdom...infering new ideas from past mistakes & sucesses and getting it right the first time shows intelligence.

I'm human and wise....miss on the third part quite often...

Schlyder · December 29th, 2008, 11:04

[QUOTE A wise man once told me, that you don't learn anything if you don't make mistakes.

[/QUOTE]

That is the right attitude. Edison said after his 1000th failure in the invention of the light bulb. "I haven't failed ... I've just discovered 1000 ways that don't work."

grimreefer · May 10th, 2009, 12:47

So which method is the proper way to do a compression test? Pushing the nozzle back into the assembled mechbox? Or pushing the piston forward with your compression parts outside the mechbox?

Can you still have a good airseal and be able to push the nozzle back into your assembled mechbox?

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December 27th, 2008, 15:53	#16
T_A_N_K Trader rating Join Date: Sep 2006	What is happening is that the oring on the piston head isn't creating a proper seal with the cylinder. You can try taking the oring off, lube it and stretch it to see if that works. If not, try using the stock oring or swap your cylinder. Once there is a good seal, you need to make sure your nozzle is sealing properly. Most quality nozzles have a oring inside, I recommend taking it out, use needle nose pliers or a dental pic, and again stretch and lube it. Once this is done, attach the nozzle to the the tappet plate and place it on the tip of cylinder head, make sure that nozzle is not completely seated on the cylinder head or it will create a false seal. Once you do that use your hand to hold the tappet plate against the cylinder, cover the nozzle with your finger and do the compression test again. if your nozzle, and piston head are sealing properly it should be very difficult to push the piston in. You don't need expensive brand name parts like Prometheus to make it work. If I have a $20 Prometheus nozzle and its not sealing and a $5 no name junk nozzle seals, I'm going to use the junk one. Last edited by T_A_N_K; December 27th, 2008 at 15:56..

December 28th, 2008, 02:22	#17
[]D[][]\/[][]D $[]D[][]\/[][]D's Avatar$ Trader rating Join Date: Dec 2005 Location: Scarborough, ON	I'm using the stock piston head and cylinder. The only aftermarket parts I got was a cylinder, spring and air seal nozzle to compensate for my longer inner barrel that I just installed. How much resistance am I supposed to feel during the compression test? Is being able to push the piston forward in the cylinder using quite some force good or am I not supposed to be able to push the piston forward at all? Because it's difficult to push the piston forward in the cylinder but I can eventually push the piston all the way to the cylinder head. I'm just kind of confussed because one guy is saying that you're not supposed to be able to push the piston forward in the cylinder at all and another guy is saying that it should be difficult to push the piston forward in the cylinder. Last edited by []D[][]\/[][]D; December 28th, 2008 at 02:24..
$[]D[][]\/[][]D is offline$

December 28th, 2008, 21:48	#20
[]D[][]\/[][]D $[]D[][]\/[][]D's Avatar$ Trader rating Join Date: Dec 2005 Location: Scarborough, ON	Yeah, I replaced the parts that I bought back with the original TM cylinder and air seal nozzle. Now I know what you guys meant when I did a compression test with those components. So basically, the spring is now the only upgraded part. When I went to chrono the gun, I was shooting around 350-360 FPS on 0.25g BBs with the new MS110 spring. Also, when I compared the Prometheus Air Seal Nozzle to the stock TM Air Seal Nozzle, I noticed that the Prometheus is shorter than the TM. Could this also have played a factor in why my FPS was below 200 before? The Prometheus Air Seal Nozzle I purchased was meant for the AK47 series and I was using it in my SIG SG 552. But I have an AK47 inner barrel in my SIG SG 552, that was the reason why I got it. Should I have just gotten the one that's made for my gun?
$[]D[][]\/[][]D is offline$

December 28th, 2008, 04:25	#19
T_A_N_K Trader rating Join Date: Sep 2006	The idea is that you not suppose to be leaking air. When you push the piston in your compressing the air, if you don't hear a hissing noise or anything then your fine. For the most part you should be bale to push the piston in 1/3 to 1/2 with resistance, till the point there is a lot, that's what you want. What will happen if you have a good seal is if you push any harder your cylinder head will pop off, however since its held in place by the mechbox it isn't the problem.

December 28th, 2008, 21:53	#21
T_A_N_K Trader rating Join Date: Sep 2006	You want to get the correct nozzle for the correct gun. Although you bought an AK length barrel, it doesn't mean your gun is an AK, it just has a longer barrel. Nozzles look similar but there are differences in them for a reason. Really the only family of guns that have interchangeable nozzles are the armalite series, some AK's, and a few others. Otherwise, pretty much everything else out there has their own specific nozzle.

December 29th, 2008, 00:40	#23
T_A_N_K Trader rating Join Date: Sep 2006	Yeah I forgot to mention Styrak is right, if its too short the nozzle won't seal, if its too long, then your gun won't feed properly. Thus why need to get nozzle specific to your AEG.

December 29th, 2008, 02:43	#25
F34N0R Trader rating Join Date: Jun 2003 Location: Saint-Georges, QC	As for the sorbo pad, it has nothing to do with proper sealing but only decreasing stress of the impact. 350 fps with 0.25gr bb & ms110 spring is good. __________________ WAR-THUG CORP.

December 29th, 2008, 11:03	#28
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	Making mistakes is human...learning from them and not repeating them demonstrates wisdom...infering new ideas from past mistakes & sucesses and getting it right the first time shows intelligence. I'm human and wise....miss on the third part quite often...

December 29th, 2008, 11:04	#29
Schlyder IronOverlord Trader rating Join Date: Aug 2008 Location: Broadview,Saskatchewan	[QUOTE A wise man once told me, that you don't learn anything if you don't make mistakes. [/QUOTE] That is the right attitude. Edison said after his 1000th failure in the invention of the light bulb. "I haven't failed ... I've just discovered 1000 ways that don't work." __________________

May 10th, 2009, 12:47	#30
grimreefer Trader rating Join Date: May 2008 Location: Victoria, BC	So which method is the proper way to do a compression test? Pushing the nozzle back into the assembled mechbox? Or pushing the piston forward with your compression parts outside the mechbox? Can you still have a good airseal and be able to push the nozzle back into your assembled mechbox? __________________

Compression Test

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