G&G GR25 low fps

[MisterX]

Hello,

Right I'm at bit of a loss. I've just upgraded my gearbox in my SR25 and it's shooting 260fps a far cry from the 460 I was aiming at.

I dunno where the problem is. I've put in:
New cylinder head
New piston head (does rattle at bit on bearing, normal? )
New tappet plate & air nozzle
New re piston
SP140 spring (was a lot of tension)
New gears
Hi torque motor
Rewired

Nothing escaped when I put finger over piston head and compressed.

Gearbox works fine, but still shooting 260.

Would hop up unit and hop rubber bring it down this much?

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[BikerEddd]

Re: G&G GR25 low fps

Turn gun upside down and put some paper towel over the mag feed part of the hop. Dry fire the gun. If the paper jumps up then you have an air nozzle to hopup leak

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[MisterX]

Re: G&G GR25 low fps

Paper didn't move a millimeter.

Only thing getting me is the piston head rattles but it was tight as I could is that normal?

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[BikerEddd]

Re: G&G GR25 low fps

Okay so we must assume that it is not a leak but the gearbox not making the pressure. Not sure about the piston head but it should centre itself anyway. Take the gearbox apart and test compression.

https://youtu.be/FlV5peGEnag

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[MisterX]

Re: G&G GR25 low fps

Right I gave that a go.

It's hard to push but I can push it in. So think there is a compression problem.

I took the rattle out of the piston head. There is no centring on it. No plastic or metal protruding to keep it centre.

Does the centralising affect it ?
What can I do to get better compression. The new cylinder head was a great fit. Needed quite bit of force to sit it in.

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[BikerEddd]

Re: G&G GR25 low fps

If it's hard to push you shouldn't loose such a large amount of power. By centering all I mean is even if the piston head can move a bit the cylinder will hold it in the correct place.

Compare the new air nozzle to the old air nozzle. Are they the same length?

Add some light silicone oil spray to the cylinder to help the seal between the head o ring and cylinder.

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[BikerEddd]

Re: G&G GR25 low fps

Also do your new gears have a sector delay chip?

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[MisterX]

Re: G&G GR25 low fps

Yeah it's centered in the rails. Already have silicone oil in. Air nozzle is exactly the same only part that was like for like replacement.

Gears are fine.

Think it could be O ring on piston head. Have one on the way gonna give that a go and post back

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[BikerEddd]

Re: G&G GR25 low fps

Worth putting your old piston head on and see what fps you get? It is a very large fps loss to be all compression.

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[MisterX]

Re: G&G GR25 low fps

Hmm just had a brain wave.

I had a M130 in before and now SP140.

The 140 is about an inch longer, would that result in a shorter draw on the piston, meaning a smaller compression chamber?

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[BikerEddd]

Re: G&G GR25 low fps

Well the gearset will still pull the piston back the same distance. I still maintain that of you are under 300 with an sp140 there is a serious air leak somewhere.

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[MisterX]

Re: G&G GR25 low fps

I'll trial and error with some spare parts and try locate the leak.

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