Piston head finger test..

[shiftline]

When i push the piston ahead it goes in easy and you can hear a kinda shhh sound but when I pull it back it is sucking and is hard to move... Shouldnt it be the opposite of this?

[shiftline]

Well it looks like the first metal tooth on the piston head has broke off which is letting air in.. all though shouldn't that be behind the piston head so should not effect the pushing of air

See Video for what i mean about sucking and not pushing





1. would the broken tooth because by miss timed gears or just wear and tear?

2. Why does the piston suck air but not push it?

[voorhees -FWA-]

air will flow in the direction it is pushed... so if you push the piston into the cylinder the column of air will push in that direction also. The "shh" sound will come from air escaping the nozzel by the ridges in your finger. If you pull the piston back, it will create a vaccuum where it will try to pull air from the ridges in your finger... The teeth on the piston will have no affect on this as the column of air is in the cylinder between your nozzel (and finger) and the O-ring on the piston head...

[shiftline]

It pushes forward easily and sounds like its letting air out, how ever when you pull the piston back its hard to move because of the vacuum.

IT sucking just not pushing air towards the air nozzle Look at the video and turn up the volume

[audi_bhoy]

If you have the chance, I'd try another piston head, if you have one. Otherwise, can you provide info's on the piston head you have? Sounds like the O-ring is working reversly that it should.

[shiftline]

Its a stock piston/piston head (TM) with a sorbo pad on the front.

Why would it suck and not push? Unless im missing something it should be compressing air on the way forward for power then should easily come back to do it all over again.. My gun was working fine for a few rounds last night (after installing a tight bore/new hopup rubber and new bushings/sorbo) then today it worked for a few shots then on fully it would quiet fireing i could hear the piston hitting the the bb was not fireing out so i figured it wasnt getting enough pressure and this is now where im at

its a TM MP5

[audi_bhoy]

I've never ran into this problem, but I'd check carefully for cylinder/cylinder head assembly, and also the piston head's O-ring to see if something would block it's normal cycling. You might try the test without the nozzle, while blocking the cylinder head to make sure it isn't just the nozzle's sealing.

[shiftline]

I took out the nozzel and covered the end of the cylinder with my hand and it still did the same thing...

The piston/piston head is a solid peice so how would it only work one way?

[G26]

Have you tried taking out the ASN and do the same test again?

[shiftline]

ASN? nozzle? I took off the nozzel/cylinder head and held it tight against my palm and did the test with the same results..

It still doesnt make sense to me the only thing that moves on the piston head is the O Ring.. could it have to do with that?

[Styrak]

First things first, replace your broken piston.

[Blackthorne]

Try pushing the piston in faster.

If you look at that gasket/o ring you will see it sits loose around the head. The gasket that sits around the piston head won't lock into place unless you move the piston assembly forward briskly, like it's being driven by a spring. You are moving to forward too slowly, and the gasket is not locking into place.

AS far as it not working in the gun, do you have enough lube on it?

[shiftline]

If anything its prob over lubed, i put a bunch of silicone gel on my finger and rubbed it all down..

The gun sounded like it was cycling and could hear the thud of the piston but bbs were not fireing out... (they were for a bit then stopped)

[coach]

what you could do is try to clean the cylinder and give the piston head oring and try it again. I've never used silicon gel but if you have another oring, just give it a little wipe/dab of llight weight silicon oil.

I'd inspect your gears also. there's a lot of metal shaving on that piston.

[shiftline]

I tried doing the piston alot faster and it does compress/ have a greater seal you can still hear a bit of air escaping but faster definly makes a difference

The gears are all stock with exception of the sector gear which i replaces a week or so ago with another stock but less worn gear... Im suspecting the sobo pad is what ultimately broke the piston tooth as it pushed it back further from the nozzle. But i still dont get why it doesn't fire 100% Is it worth buying a new cylinder set? Modify has them for about 75$ with piston/piston head, cylinder/nozzle ect