Piston not travelling all the way forwards?

[Boo-Sabum Ben]

Hello chaps.

Got myself a cyma MP5 to downgrade and play with. All has gone well, except now the piston doesn't travel as far forwards as it used to. I noticed when the blowback bolt wasn't moving as far forward after each shot. It's still on the piston when it arrives.



I think it may also explain why I lost about 50 fps when I worked on my sopmod. So it's something I'm getting fundamentally wrong across both gearboxes, but they both still work fine as well.


What's causing it?

[dadio]

Re: Piston not travelling all the way forwards?

have you fitted sorbo pads or silent piston heads?

[Boo-Sabum Ben]

Nope. Literally spring in, spring out.

[Darkmikey22]

Re: Piston not travelling all the way forwards?

have you made sure when putting the new springs in you've set the teeth correctly so that the piston is all the way in and the teeth are free from the gear teeth?

[Boo-Sabum Ben]

I'm not too sure on that one. I always make sure that the sector gear is in the 3 o clock position.

Even so, wouldn't the set up just correct itself after the first shot?

[Darkmikey22]

Re: Piston not travelling all the way forwards?

nope. i tend to make sure the piston is all the way in and that the sector gear has the teeth pointing down (free from the piston) so that the tappet plate will sit freely over the sector gear too. then when assembled the first tooth on the sector gear will pick up on the first tooth of the piston. get it wrong and i have seen it strip teeth all over the place.

[humphriesryan]

Re: Piston not travelling all the way forwards?

Should do but not always lol
Is the blow back working fine if not can affect the piston due to the is sapoe to acape through the ported hole of cylinder, nozzle and blow back system ...
Could be dirt in the cylinder it's getting snagged on or something broke ....
Or main thing is the ale needs doing

[Boo-Sabum Ben]

What the hell are you talking about.

As there's a nightgame on Tuesday I'll leave it as is for now, will probably try and rectify it before the weekender!

[Boo-Sabum Ben]

Is there anything really obvious I've missed? I'm fairly sure it's me putti something in slightly the wrong place. Does anyone have a checklist of exactly where each part should be aligned with so I can see what might be causing it?

All the open gearbox pictures show the piston not fully in the cylinder anyway.

[humphriesryan]

Re: Piston not travelling all the way forwards?

http://m.youtube.com/watch?v=WhCwDcC8t2g

[Boo-Sabum Ben]

Probably not gonna be able to watch that, on mobile Internet while I wait for Internet to arrive in the flat

Would somebody be able to tell me what they say in the video?

Also, discovered it only happens in semi. I can time shot trigger right on full auto that it stops at the end of the cycle and the prison and bolt have travelled all the way. A cut of. Lever timing problem?

[dadio]

Re: Piston not travelling all the way forwards?

when you set the sector gear to 3 o-clock do you set the reverse latch on the bevel gear?because the reverse latch should be engaged when the sector gear is at rest,also i usually set to 2 o-clock,in any case it seams to be starting its next stroke.

[Boo-Sabum Ben]

I just leave the reversal latch against the gear. I don't move it into a specific position. Doesn't it just prevent the gears going backwards? It doesn't perform any other function as far as I know?

[dadio]

Re: Piston not travelling all the way forwards?

just how i was shown i guess but its supposed to prevent leaving the spring partially compressed when stored,like always shooting on semi before storage etc.

[B.E.N.]

Re: Piston not travelling all the way forwards?

I've said it before and I'll say it again, You simply can't "short stroke" a piston without removing teeth from the sector gear. The rack on the piston and the teeth on the gear correspond for this reason. Unless you some how manage to reassemble the gearbox with the piston halfway onto the cylinder, with the sector and piston teeth meshed and the AR latch locked into place, you can't do it.

Basically, the piston would get ripped up pretty sharpish if the sector gear was engaging the piston without it having moved fully forward.

Guns of more powerful batteries will often "over run" slightly anyway.