Low fps could it be cylinder related?

[Rogerborg]

1 hour ago, ak2m4 said:

@Pollynator_bravo2 clean that inner barrel and wash that rubber 

 

We have to maintain our toys?

 

[Dan Robinson]

16 minutes ago, Rogerborg said:

 

We have to maintain our toys?

 

 

Never was a character so true to life.

[father of a 15 year old]

[Pollynator_bravo2]

6 hours ago, ak2m4 said:

@Pollynator_bravo2 clean that inner barrel and wash that rubber 

Yeah fair point. Not done anything to it since I brought it off a seller. I think it was thrown together with bits from the Airsoft fair

[Pollynator_bravo2]

On 02/08/2024 at 09:38, Lozart said:

 

 

Timing does indeed mean the cycle of retracting the nozzle to allow the bb into the hop unit, then allowing it forward to seat the BB into the hop before the piston comes forward. If you're not getting a feeding issue that should be OK but if the nozzle isn't actually seating on the feed lips of the hop rubber properly you may be getting an air leak.

 

The chamfered tip of the nozzle should seal into the end of the hop rubber (the feed lip if you will). An easy test is to reassemble the gun, turn it upside down and place a small piece of paper over the feed tube. When you fire the gun the paper should move only minimally, if it blows off then there is air escaping down the feed tube.

 

Also - it may be the camera angle but your barrel doen't look straight in your hop unit - it may need twisting slightly to line it up.

 

So the paper moved a fair bit so I’m guessing air is escaping ?‍♂️

 

 

[Lozart]

On 03/08/2024 at 11:59, Pollynator_bravo2 said:

So the paper moved a fair bit so I’m guessing air is escaping ?‍♂️

IMG_3676.mov 10.52 MB · 8 downloads  

 

 

We have a winner!

 

Tip of the nozzle isn't sealing with the rubber.

[Colin Allen]

On 03/08/2024 at 11:59, Pollynator_bravo2 said:

So the paper moved a fair bit so I’m guessing air is escaping ?‍♂️

 

The nozzle is not fully engaging with the hop rubber lips.  Is the hop unit pushed fully back against the gearbox?  If it isn't, use some O rings in front of it to push it back.  If it is, try longer nozzles or get a variable nozzle.

[Pollynator_bravo2]

3 hours ago, Colin Allen said:

The nozzle is not fully engaging with the hop rubber lips.  Is the hop unit pushed fully back against the gearbox?  If it isn't, use some O rings in front of it to push it back.  If it is, try longer nozzles or get a variable nozzle.

It’s a weird one as I grabbed the old gear box that came out of it and serviced it fully. When I opened it up the tappet plate looked different. It has a moon shape on the tail end and there is a delay chip however the nozzle is shorter than what I had in the eon gb. When I fitted it all back together (with a clean inner barrel and bucking) I got 335 fps and 1.28j (no hop applied) ?‍♂️??‍♂️

 

I guess this is an easier problem to fix the the latter lol

images are of the gb that came with the gun when I brought it 2nd hand

[Colin Allen]

51 minutes ago, Pollynator_bravo2 said:

It’s a weird one as I grabbed the old gear box that came out of it and serviced it fully. When I opened it up the tappet plate looked different. It has a moon shape on the tail end and there is a delay chip however the nozzle is shorter than what I had in the eon gb. When I fitted it all back together (with a clean inner barrel and bucking) I got 335 fps and 1.28j (no hop applied) ?‍♂️??‍♂️

 

I guess this is an easier problem to fix the the latter lol

images are of the gb that came with the gun when I brought it 2nd hand

That seems to be the best way forward.  I have never seen a tappet plate like that before.

[Lozart]

13 hours ago, Pollynator_bravo2 said:

It’s a weird one as I grabbed the old gear box that came out of it and serviced it fully. When I opened it up the tappet plate looked different. It has a moon shape on the tail end and there is a delay chip however the nozzle is shorter than what I had in the eon gb. When I fitted it all back together (with a clean inner barrel and bucking) I got 335 fps and 1.28j (no hop applied) ?‍♂️??‍♂️

 

I guess this is an easier problem to fix the the latter lol

images are of the gb that came with the gun when I brought it 2nd hand

 

 

Wow, that is OLD!

 

The different design of tappet plate would certainly account for what you're seeing. The fix will still be a longer nozzle though as you can't get tappet plates like that any more.

[ak2m4]

3 minutes ago, Lozart said:

Wow, that is OLD!

 Jurassic Army.  Look at the size of the vent holes in the piston head.  Length of the cylinder head shaft looks quite long as well.  Looks all nice and clean, cheap to fix up and run

[Lozart]

3 minutes ago, ak2m4 said:

 Jurassic Army.  Look at the size of the vent holes in the piston head.  Length of the cylinder head shaft looks quite long as well.  Looks all nice and clean, cheap to fix up and run

 

I was just thinking that, it's in bloody good nick for its age!

[Colin Allen]

1 hour ago, Lozart said:

 

 

Wow, that is OLD!

 

The different design of tappet plate would certainly account for what you're seeing. The fix will still be a longer nozzle though as you can't get tappet plates like that any more.

He could try fitting a standard tappet plate and seeing how that goes; it might still need a different nozzle.

[Lozart]

1 minute ago, Colin Allen said:

He could try fitting a standard tappet plate and seeing how that goes; it might still need a different nozzle.

 

Absolutely, other than being drier than a nuns fanny it seems to be in pretty good nick.

[Colin Allen]

2 hours ago, Lozart said:

 

Absolutely, other than being drier than a nuns fanny it seems to be in pretty good nick.

It is surprising how good some gearboxes look after a long period.  I opened up the lad’s blowback G&G AKM on Sunday to deal with a low power issue, after it had not been opened for many years.  Apart from a worn piston head O ring, it was pretty much perfect.

 

it was still a bugger to do due to the stupid pneumatic blowback system.

[Pollynator_bravo2]

On 06/08/2024 at 10:38, Lozart said:

 

Absolutely, other than being drier than a nuns fanny it seems to be in pretty good nick.

That was before being cleaned and lubed up. Was wetter than Gemma Collins mouth in greggs 

On 06/08/2024 at 12:59, Colin Allen said:

It is surprising how good some gearboxes look after a long period.  I opened up the lad’s blowback G&G AKM on Sunday to deal with a low power issue, after it had not been opened for many years.  Apart from a worn piston head O ring, it was pretty much perfect.

 

it was still a bugger to do due to the stupid pneumatic blowback system.

What’s the correct O ring size for the piston and cylinder head ?

[Colin Allen]

1 hour ago, Pollynator_bravo2 said:

What’s the correct O ring size for the piston and cylinder head ?

Cylinder head is generally 22mm OD, 1.5mm cross section.
Piston head is generally 24mm OD, 2.4mm cross section

AK2M4 sells some slightly larger piston head O rings for slightly larger cylinders; they are 24mm OD, 2.7mm cross section.

Edited August 7, 2024 by Colin Allen

[Pollynator_bravo2]

On 07/08/2024 at 21:16, Colin Allen said:

Cylinder head is generally 22mm OD, 1.5mm cross section.
Piston head is generally 24mm OD, 2.4mm cross section

AK2M4 sells some slightly larger piston head O rings for slightly larger cylinders; they are 24mm OD, 2.7mm cross section.

Epic thanks for this. Next job on the list ?

[Big Cheese]

Compression test the cylinder. With the cylinder out of GB with tappet and nozzle fitted. Hold finger over nozzle and push piston down into cylinder. It should stop 2/3 way down when all air is compressed. If it doesn't replace the piston oring.