Feeding or air seal, a conundrum

[Jaylordofwaargh]

So, as per title this is the state of my m4 variants I have (in the ics), in the search of more power, upped the spring changed piston rack to full metal, when it went back together, this lead to a feeding issue, so I changed to nozzle, whilst I was in there I wasn't happy with the air seal so I changed the piston head and cylinder head.  

Thing is though, I went for a vented piston head and now I think the air seal is worse! 

So what is the deal with vented heads, was a simply distracted by the shiny colours. Is it a case of buying a crono and trying each piece in isolation? (Please don't be this option)

Any thoughts welcome

 

[ak2m4]

they're all vented, it's what pushes out the piston head oring to create a solid air seal, it's just some have more vents than others but generally it doesn't make much difference.  Ideally you need a chrono if doing any gearbox upgrades.

Did your original piston head not have any vents?

 

[Rogerborg]

Upgrades, eh?

Same as with anything else in airsoft, it's best to change one part at a time and then test objectively.

Same as with anything else in airsoft, ain't nobody got time fo' that.

What I would suggest is ensuring that the o-ring is loose, and I mean looser than you'd think is necessary. You can stretch it over the cylinder to slacken it up, or replace with something that might be a bit more generous than stock. I use BS910 19.18mm x 2.46mm rings.  Nitrile, but I'm sure someone will demand Viton® is the One True Material.   

Keep at it, I've seen a shocking 1.3J on 0.28g from an M100 spring, 228mm 6.01mm barrel, rotary hop, Maple leaf bucking, and stock CYMA gearbox components just with extra holes drilled in the head, a replaced o-ring, and a little silicone grease.

 

[Adolf Hamster]

they're all vented

I have seen ones without dedicated vents, although in that case friction and leakage around the front end usually does enough of the same job

 

[Jaylordofwaargh]

What I'm hearing is start again and do a piece at a time.....

Damn it. 

From what I can tell, no the OG was not vented, maybe I wasn't looking hard enough. 

The o ring is loose, back to the drawing board, and a chronograph on order soon. I'll just take it in "as good as I can get then hope they maybe have a spare rental on Saturday. 

Thanks gents

 

[Lozart]

I'm sure someone will demand Viton® is the One True Material.   

I mean....it is. It's also complete overkill in our application!

What I'm hearing is start again and do a piece at a time.....

Yup.

Always change one thing at a time if you're not sure where a problem is.

 

[ak2m4]

One True BRAND ?

You're right, not needed.  Most Nitrile comes with decent anti-oil protection aleady.  The same Viton / FKM oring is often 5% thicker so it's better used when looking to make up a little extra space.

 

[Leo Greer]

Non-vented piston heads used to be the standard. And they do work, just not at higher RPS. At low RPS they're able to simply pull in air through the nozzle, but above about 18-20 this ceases to work. There are some mfgs that still use them.

Seconds on a chrono and trying each piece individually. This is by far the best way to see the actual effect of what you're doing. Without a chronograph it's just guesswork.

 

[Sewdhull]

Nitrile, I think, is the best for our application with conditions being far from the extremes viton might do better in, the data sheets say viton has less tear strength than nitrile which may well be relevant in Airsoft, where temp extremes and exposure to damaging chemicals is less an issue.

I tried shore 70 Vs shore 90 and got a better seal with 70 using the push test.

This was a 19 X 24 o ring.

I don't know if vented heads are better than unvented ones, they all seem to rely on the head moving forward, pushing the o ring against the back of the groove, from the friction on the cylinder and sealing on that rear part of the groove.

I imagine with no sealing on the rearward travel there's less effort needed to recharge the cylinder area with air.

If the cylinder isn't a full type perhaps that's moot.

 

[Jaylordofwaargh]

I do love the ics split gearbox, like, a lot. Makes it so simple to dive into the cylinder section of the box. 

So, I went back in and cleaned all the grease off various places where it had no right to be....I made some mistakes.....and started again with both cylinder heads, turns out that was my issue both were leaking from the front and not sealing. Cue the silicon grease 

Next up is seeing whether or not I need to have a slightly longer nozzle on one of them...

 

[Jaylordofwaargh]

Most of my postings on this thread is going to be "ok, so..."

Ok, so.... Got to driver, the lads TM MC51 came in at a respectable 297 (.25's), great start to the day. 

Took both of my paperweights to see if I was using them or not.

Or not, as it turns out. The ics with a full seal now shoots 1 shot with a new mag at a spicy 354 on .25's, the OG spring will be going back in there....

The Caa m4 with the king's arms gearbox...I think need to go back in and have another look at the trigger. When pulled, there was no spin from motor but with half a pull and carefully holding I can get it to fire but lacks consistency. So another one I need to crack open again....

Any tips on what to look for as to trigger contacts and placement?

 

[Sewdhull]

Trigger contacts oxidise over time, arc and then fail to make contact. But they also get hot and the plastic holding them in place melts and the contacts move.

The exterior contacts if you have them are unnecessary.

Replacing the contacts is advised and also the fire selector plate if the copper part is used.

My mp5 had the copper contacts on the trigger contact block and this should be avoided.

View attachment 124209

Get one without contacts if you have this version.

You will see the state of the exterior contacts after you take selector plate of or to the safety position.

From what you say it sounds like the selector plate contacts, but the trigger contact can also behave this way also.